The Science of Tasting

Written by GuildSomm, Scientific Topics Reviewed by Dr. Jamie Goode, PhD

We observe what we are prepared to observe.
– Louis Pasteur

Introduction

Tasting skill is integral to the sommelier profession. Buying positions necessitate analysis of value through tasting, and positions on the floor require effective communication of a wine’s qualities. Happily, tasting is a learned skill; it is honed and practiced rather than innate. Inexperienced tasters may find every avenue of excuse—physiological and otherwise—to deter advancement, and progress may seem frustratingly slow in the beginning. Throughout their course of study, however, sommeliers will taste thousands of wines, and with some work a useful understanding of the language of taste eventually emerges. And when learning the language of taste, tasting blind is an important practice.

Why? One notable (and highly visible) importer disregards the practice, diminishing it as “irrelevant prowess…hardly a skill that will be put to use in a wine career,” before backpedalling slightly, and admitting that it may be as useful as playing scales—though hardly the equivalent of real music. Of course, blind tasting is frequently less helpful to those with wine (stories) to sell, but enormously important to those who buy based on innate quality. Blind tasting allows one to interpret quality absent the noise of reputation. Expectation changes the experience. When blind tasting, one learns how to describe a wine as it is, not as it should be. Of course, a good sommelier understands the classic wine profiles of the world, and therefore can link what appears in the glass to an appropriate, logical conclusion. Learning to aptly describe wine, in a way that can be meaningfully conveyed to others, is the core value of blind tasting. The conclusions—grape variety, region, vintage—are just logical aftermath.

This is not to suggest that all tasting exercises should be blind. In the rush to practice examination techniques, sommeliers may forget that non-blind tasting formats can be instrumental to understanding and success. If a taster does not understand the classic profile of Rheingau Riesling, or the major sensory differences between Spanish Albariño and Austrian Grüner Veltliner, then no amount of blind tasting guesses—right or wrong—is going to change that. Tasting with the label visible allows a sommelier to understand what classic wines should look like, and to fine-tune assessments of structure and aroma.

This guide is meant to be helpful for all tasters at an advanced level. The terminology is that of the Guild of Sommeliers and not necessarily of any specific examining body such as the Court of Master Sommeliers.

The Tasting Glass

Whether or not glass shape is as consequential as the major stemware companies would suggest, a vessel’s size and shape do impact perception, so sommeliers should make an effort to taste from the same type of glass whenever they are professionally analyzing wine. Using a single glass design for analytical tasting will enable a sommelier to calibrate his or her own sense of structure and to develop a sense of aromatic intensity when comparing and contrasting wines. In general, the glass’ bowl should be large enough to permit vigorous swirling, and the lip of the glass should curve slightly inward from the bowl. Tasting glasses must be transparent and unadorned to permit unobstructed study of color, and they should have stems. Many professional sources recommend an “ISO” (International Standards Organization) stem as the best all-around tasting glass for professionals, but the Guild of Sommeliers regards this as a poor choice, and too small to be of real value.

Wine Temperature

When critically assessing wine, the liquid’s temperature affects taste and olfactory assessment. Structural elements and aromatics are dampened and/or enhanced with changes in temperature. As a wine rises in temperature, aromatic compounds (and ethanol) become increasingly volatile. The wine will therefore give off a greater intensity of aromatics, and a headier, sweeter whiff of alcohol, as it gets warmer. While this may improve the aroma of the wine in the short term, delicate nuances may be quickly lost, and the wine may develop poorly in the glass. In addition, lower temperatures may suppress perception of sugar—there are conflicting studies on this subject—and cold enhances bitter and astringent phenolic sensations. Cold temperatures also allow sparkling wines to retain effervescence for a longer duration. Higher temperatures cause the wine to show more alcohol and sourness.

For critical tasting, whites and rosés are best served slightly chilled but not cold (50-55° F) and reds are best served between 58-65° F. Alternatively, some suggest tasting all wines, white and red, at a high cellar temperature of 58-60° F. Do not allow temperature (or choice of glassware, or any other exterior mechanism) to become a crutch, though—if a wine is too cold, warm it up in your hands.

Visual Appearance
The Nose
The Palate
Blind Tasting Conclusions

Visual Appearance

The wine’s visual appearance may hint at grape variety, condition of fruit, and winemaking technique. During this phase of analysis, a taster may develop suspicions but is cautioned against making final confirmations, as a wine’s visual cues may be deceptive. When addressing visual appearance, it is best to view the wine against a white backdrop, from the top down, while holding the stem at a 45° angle. Examining a wine under natural lighting gives the most unadulterated sense of color, but any white light source is acceptable.

For a seasoned taster, spending longer than 15-20 seconds examining a wine’s visual appearance usually becomes a distraction.

Color/Hue

Red and white wines extract color from various polyphenols in grape skins. Oak usage, oxidation, age and other factors also impact color.

Red wine color results from the presence of anthocyanins, colored phenolic compounds present in many species of the plant kingdom, ranging in hue from orange to purple. The accumulation of anthocyanins in red grapes during and after véraison is enhanced by sunlight, but actually inhibited by heat—cooler growing seasons may actually produce darker-colored wines than hot ones. Black fruits display particularly high anthocyanin content; therefore those fruits that ripen into darker-colored berries, such as Cabernet Sauvignon or Syrah, will produce more deeply colored wines than red berries like Pinot Noir or Grenache. However, color is a complicated subject, and a continuing area of research. Anthocyanins are the root cause of red color in grapes and must, but long-term color stability requires the formation of more complex pigmented polymers—aggregates of anthocyanins and other polyphenols (like tannins) in the wine.

Sulfur dioxide and pH affect the impact of anthocyanins in red wines. Post-fermentation sulfur dioxide additions bleach anthocyanins, stripping red wines of some depth of color. Lower pH moves the pigments into the redder end of the spectrum, whereas higher pH causes anthocyanins to appear purple or blue. Despite the association with pH, however, tasters are never advised to make predictions of acidity on color alone.

Winemaking decisions, such as length of maceration, affect color. Anthocyanins dissolve more readily in water than other polyphenols (e.g. tannins) and are thus extracted first. Pinot Noir winemakers take advantage of the water solubility of anthocyanins to build color during pre-fermentation cold macerations. During fermentation, color extraction occurs before tannin extraction, which requires a certain level of ethanol to enhance solubility. Color will actually decrease during the longer macerations common in parts of Italy (e.g. Barolo and Barbaresco), but such wines will retain their level of color for a longer time in the bottle.

Oxidation and oak are key factors in wine color. As various polyphenols oxidize, the wines undergo color change. White wines darken as they oxidize, and over time shift from lemon to gold to amber to brown. Red wines, on the other hand, lose color intensity as they oxidize, shifting from purple to red to garnet and brown. The degradation of color via oxidation is generally a slower process in red wines, and grape varieties can differ dramatically in their sensitivities to oxidation. Severe examples of oxidative browning in wine include older Tawny Port (red) and mature Sauternes (white). Botrytized white wines in general show a marked oxidative hue, courtesy of laccase, an enzyme produced by Botrytis cinerea that oxidizes a wide range of phenols in the must and is relatively unaffected by sulfur dioxide additions. Long aging in oak will lead to oxidation of color. On the other hand, oak tannins, plentiful in new barrels but scarce by the vessel’s fourth or fifth use, likely stabilize and augment wine color. Compare a newly released, garnet-toned Gran Reserva Rioja aged in used American barrels with a modern, ruby or nearly purple Ribera del Duero, aged for just a year or so in new French oak.

White wine color is generally the result of exterior factors rather than intrinsic polyphenols, although yellow-, green- and orange-pigmented compounds present in skins and pulp may create slight variations in base white wine color, resulting in hints of green and other colors. White wines aged in new oak barrels frequently display a golden hue.

Acylated Anthocyanins?

Pinot Noir produces red wines that are noticeably lighter in color than those made with most other varieties. This is because the grape lacks what are known as acylated anthocyanins. There are five different anthocyanins in Vitis vinifera: cyanidin, petunidin, delphinidin, peonidin and malvidin. Their proportion and levels in grape skins (where they are found) is influenced by the variety and the terroir.

Anthocyanins undergo chemical modifications that can make them more stable. For example, they can bind with sugars to form glucosides. Interestingly, non-vinifera varieties can produce diglucosidic anthocyanins that are much more stable, and their presence in wine has been used to check for the use of hybrids, which are not allowed in French AOP wines.

One such modification is called acylation, wherein sugar residues attached to the anthocyanin are “acylated” by the addition of aromatic or aliphatic acids, making them more stable. This reaction is catalyzed by enzymes called AATs (anthocyanin acyltransferases). Pinot Noir lacks the ability to form acylated anthocyanins, and so produces wines that are lighter in color. This is because acylation both increases the stability of anthocyanins and also increases their extraction during maceration through enhanced solubility. Without the protection of acylation, anthocyanins can lose their color in wine.

It is not clear from the literature whether other naturally lighter-colored red grapes such as Nebbiolo and Grenache also lack acylated anthocynanins, but this is a possibility. More likely, they have some acylated and a relatively higher proportion of non-acylated anthocyanins.

– Jamie Goode

Clarity and Turbidity

The clarity of wines is affected by density (concentration) of color and the liquid’s turbidity. Turbidity indicates a measure of haziness caused by microscopic solid particles in suspension within a liquid. Suspended solids affect a wine’s clarity, rendering the liquid translucent rather than fully transparent (clear) by altering its ability to refract light. Turbidity is not affected by visible sediment, nor is it dependent on color. Opacity, on the other hand, is a result of highly concentrated, dark color. In scientific terms, an opaque object does not allow any light to pass through it; in tasting the term is used to refer to those deeply colored red wines which are not possible to see through. An opaque wine may not show high turbidity, or haziness, but it is nonetheless not clear.

“Clear”: Wines without apparent turbidity are termed clear. These wines may be red or white, but the density of color in such wines does not render them opaque. Filtered wines tend to be clear, rather than turbid.

“Turbid”: Wines with apparent haziness or cloudiness. Turbidity in young wines may indicate a lack of filtration and/or fining.

“Opaque”: Wines in which turbidity or high density of color leave the taster completely unable to see through the liquid.

Rim Variation

As wines age, the color at the rim of the glass will begin to show signs of oxidation before the color at the wine’s core. Greater color gradation will be apparent in mature wines. A youthful, opaque, dark purple red (high quality Napa Valley Cabernet Sauvignon) may show a thin sliver of bright pink around the rim; after two decades of aging the wine’s rim will show a wide garnet band, yet the core will retain a purplish—if less vibrant—hue. Rim variation is a less obvious feature in white wines.

In wine parlance, the terms “rim” and “meniscus” are often used interchangeably, although the meniscus itself refers to the liquid’s concave curvature in the glass, and is represented by a thin band of watery, clear liquid beyond the rim. (see “surface tension” section below for more information).

Visible Sediment

Wines may show visible particles, or sediment, in the glass. Visible sediment does not affect the turbidity of the wine. Visible sediment is common in older red wines, and consists of precipitated tannins, anthocyanins, and other solids that fall out of suspension in the wine. Tartrate crystals—flakier, large potassium bitartrate crystals and finer calcium tartrate crystals—may appear as visible sediment in both white and red wines of any age, signaling that the wine was not cold-stabilized prior to bottling. Young, unfiltered red wines may throw visible sediment as well, so the presence of sediment is not always an indication of age.

Spritz and Effervescence

Slight spritz may occur in young wines bottled early. This phenomenon typically occurs in white wines, such as Austrian Grüner Veltliner or Spanish Albariño, and results from an excess of dissolved carbon dioxide that becomes sealed in the bottle. It usually bears no relationship with the wine’s quality or lack thereof, and it is especially common in screwcap-closed bottles. Nouveau and other young carbonic red wines often display a light spritz. On rare occasions, spritz may indicate a flaw, such as in-bottle secondary fermentation.

Purposefully sparkling wines are effervescent, generating continuous streams of bubbles that rise from various nucleation sites within the glass. Dr. Tony Jordan, CEO/Winemaker of Domaine Chandon Australia, explains the process: “Bubble formation requires the presence of nucleation sites with minute air pockets trapped inside them. The pockets of gas arise because of incomplete wetting of the nucleation sites when the wine is poured into the glass. These are now believed to be hollow cellulose fibres from paper and cloth rather than faults in the glass itself. CO2 diffuses into the pockets of gas until they grow big enough to lift off and interestingly when they do a small pocket of gas is left so another bubble forms from the same site and so on, hence the familiar stream of bubbles from one site. The nucleation sites can be stuck to the glass or floating in the wine.”

Tearing

The tears, or legs, of wine are small rivulets that appear along the film coating the side of a glass after swirling the wine. These may form quickly or slowly, and they may be more or less defined. Slow-forming, slow-moving, well-defined tears support a case for high alcohol in the wine, but they have no relationship with sugar, glycerol, or viscosity. Tears are just a predictor of alcohol, and not a very exact one at that. When examining tears, do not swirl the wine; rather, tilt the glass back to form an observable film without vigorous swirling. Many tasters also register saturated color, or “staining,” in the tears of red wines as a sign of a highly extracted wine style. While it is true that opaque, deeply extracted red wines tend to show noticeable color in the tears, the presence of “staining” in the tears is not a separate phenomenon from the density of color in the wine, and it is especially important not to draw conclusions on climate simply from stained tears (some assume warm climates necessarily produce more extracted wines, in error). In fact, red wines from cooler vintages may have deeper color, and reflect this color in the tears.

The science behind tearing

Tears occur because of the varying evaporation rates and levels of surface tension in water and alcohol (ethanol). Surface tension allows a liquid to cling together, to adhere to itself rather than an exterior object. The beading of water on a recently waxed car is an example of the cohesive force of surface tension at work: the water molecules are more attracted to each other than they are to the wax, and they pull inward in a neatly spherical shape. Ethanol has a lower surface tension, and will not form as large a bead; instead it spreads out faster, wetting the surface sooner than water.

Some exterior surfaces will exert a stronger adhesive force than others, and will more easily overcome the surface tension of a liquid. Water and ethanol easily adhere to glass, for instance, because it contains silica—composed of silicon and oxygen—and the latter element readily attracts hydrogen compounds, e.g. water and ethanol. Thus, wine does not easily bead on glass, but wets it instead; swirling a wine creates a thin film that adheres to the side of the tasting glass. Wine’s preference to adhere to the glass rather than cohere to itself is also visible in the wine’s slightly concave meniscus; if the wine’s force of surface tension was greater than the adhesive force exerted by glass, its meniscus would be convex.

This is where things get a bit more complex: the thin film of liquid adhering to the glass has a much greater surface area than the wine itself, and therefore both water and ethanol evaporate much more quickly from the film. Alcohol has a faster rate of evaporation than water, increasing the surface tension in the uppermost film. The suddenly stronger surface tension in the film exerts an attractive force on the water-rich liquid around it and the wine in the glass below, defying gravity and pulling it upward into the film. The liquid contracts into roughly spherical shapes, and the force of gravity begins to overcome the adhesive force of the glass, distorting the shapes into “tears” that slowly fall down the side of the glass. Wines of higher alcohol content require more ethanol to evaporate prior to the formation of tears than wines of lower alcohol content, so tasters may suggest that “slow-forming” tears are the result of a higher level of alcohol in the wine. However, temperature of the glass affects tearing—higher temperatures lead to greater rates of evaporation—and soapy residual on the glass will diminish the overall surface tension of the liquid and affect its adhesion to the glass.

The Nose

Some tasters prefer to take several short, quick sniffs of the wine; others prefer to inhale deeply. Some prefer to keep the mouth open while inhaling, opening both olfactory and retronasal pathways to incoming aromas. Whatever your method, don’t start with your nose too far in the glass—alcohol vapors tend to collect in the bowl of the wine glass and irritate the nose, preventing vital but subtle aromas from making their presence known. And try smelling the wine before vigorously swirling it—aeration may be necessary for a closed wine but many wines can offer vital clues to their character without it. Finally, don’t overdo it: nasal fatigue will sink an otherwise successful tasting. Try to ascertain as much about the wine as possible in as few inhalations as necessary. Often, when we continue to smell the same wine over and over again, to excess, it is because we are trying to taste instinctively rather than deductively—“What is this wine?” rather than, “What is the character of this wine?”—and poor decisions result. Try forcing yourself to smell a wine only three or four total times, and make an entire assessment on the nose without continually going back to the well. This will build endurance for longer flights.

WINE FAULTS

Before assessing the wine’s nose, a sommelier must first determine if the wine is sound. In the modern age of winemaking, many of the common and obvious faults of yesteryear have been greatly reduced or wholly eradicated through sounder and more sanitary winemaking practices. Cork taint remains one of wine’s most expensive problems and wine drinkers’ greatest frustrations, but few other major faults in wine are absolute and inarguable. The presence of Brettanomyces bruxellensis, for instance, may generate off-aromas for some but add to a wine’s animal, savory character for others. At high concentrations it is generally off-putting but at lower concentrations it may provide complexity. Experiences and expectations tend to shape perceptions: a fan of young, clean, fruity whites may deem a purposefully oxidative style from the Jura flawed, despite the winemaker’s intentions. Nebbiolo fans may find volatile acidity appropriate, even classic, in Barolo, yet unacceptable in other wines. General sensibilities and even thresholds of perception for various foul-smelling compounds in wine can vary from person to person, and some compounds regarded by modern drinkers as faults have been historically associated with terroir. Beyond cork taint—a fault at any perceivable level—all of the following faults may give pleasure to some and cause others to recoil, depending on their relative concentrations in the wine. While most faults in wine may be difficult to categorize without exception, remember that the microbial or chemical culprits behind flaws not only arrive with their own rank odors, they also suppress the more positive, expected aromas of the wine.

Cork Taint

2,4,6-trichloroanisole (TCA) and 2,4,6-tribromoanisole (TBA) have been identified as principal causes of the musty off-odors associated with “cork taint.” TCA and TBA are haloanisoles, containing chlorine and bromine atoms, respectively, produced by the degradation of halophenols by fungi and bacteria. Halophenols are present in certain manmade chemicals (chlorine bleach, wood preservatives, flame retardants) and they appear in chlorinated drinking water, but they do not occur naturally in wine. Instead, halophenols from exterior sources are detoxified and transformed by fungi and bacteria into foul-smelling (if otherwise harmless) haloanisoles, which taint the wine. In the past, chlorine bleaching was standard practice for the cork industry, and corks were easily contaminated by TCA. Today, scientists understand that the cork is the pathway, not the cause; barrels and whole cellars can suffer from systemic contamination. Other haloanisoles, such as 2,3,4,6-tetrachloroanisole (TeCA) and pentachloroanisole (PCA), have been implicated in “corked” wines, and newer research suggests that certain pyrazine compounds may result in similar, musty odors. The list of suspects responsible may be growing, but the effect is the same: suppressed fruit, bitterness, and odors likened to wet newspapers, damp basements, and mold. From a business standpoint, “corked” wines should be rejected, and returned for full credit to the supplier.

Brett

Brettanomyces bruxellensis, a yeast native to the Senne Valley of Belgium, is integral to the flavors of certain styles of beer but is generally a less welcome intruder in wine. Known colloquially as “brett,” the microbe is found naturally in the vineyard, and it is scientifically regarded as a spoilage yeast. Like Saccharomyces cerevisiae, the yeast species responsible for primary fermentation, Brettanomyces metabolizes sugars, including cellobiose—a sugar molecule present in the toasted wood of new oak barrels—and otherwise unfermentable sugars in finished wines. It can also use ethanol and amino acids as a food source. Although it prefers oxygen, Brettanomyces is able to survive in anaerobic environments, and it is highly adaptable, creeping into wines after the more aggressive S. cerevisiae’s work is finished. It can infect barrels and entire wineries; once entrenched it is difficult to eradicate. Brettanomyces may inhabit new oak barrels with elevated levels of cellobiose, or improperly cleaned older barrels. It prefers higher levels of pH and polyphenols and lower levels of sulfur dioxide. Thus, barrel-aged reds are in general the most susceptible to contamination. Once in a wine, brett may “bloom” in the bottle, producing from polyphenol precursors three signature spoilage compounds: 4-Ethylphenol (4-EP, associated with Band-Aid aromas), 4-Ethylguaiacol (4-EG, associated with clove and medicinal scents), and 4-Ethylcatechol (4-EC, associated with sweaty, horsy aromas). In addition, Brettanomyces produces acetic acid, isovaleric acid—a volatile fatty acid marked by sour aromas of barnyard and bile—and tetrahydropyridine compounds, the source of “mousy” odors in wine. Overall, aromatic compounds produced by Brettanomyces mask varietal character at high concentrations, and may be deeply off-putting, but for some they add complexity at lower levels. In 2013, Linda Bisson of the University of California at Davis released the “brett aroma wheel” after extensive research on 83 different strains of the organism. A tasting panel found that 17 strains produced totally positive aromas. The debate continues.

Volatile Acidity

Acetic acid bacteria convert both glucose and ethanol to acetic acid; essentially, such organisms spoil wine by turning it to vinegar. Unlike the fixed tartaric and malic acids, acetic acid is volatile: it vaporizes and gives off vinegary aromas. Two species—Gluconobacter oxydans and Acetobacter aceti—are responsible for the production of acetic acid during and after fermentation, respectively. G. oxydans enters the winery on grape skins, and arrives in much greater numbers on moldy fruit. It prefers a sugar-rich environment and is highly active during primary fermentation. However, the population of G. oxydans steadily decreases after fermentation, whereas the number of A. aceti bacteria rises sharply several months after malolactic fermentation. This strain is most associated with volatile acidity. Acetic acid bacteria require oxygen to grow, and populations of A. aceti spike during periods of racking or other oxidative procedures. Barrels that are infrequently topped-off are prime targets for Acetobacter, and it may grow in bottled wines with imperfect closures. In addition to Acetobacter and Gluconobacter, lactic acid bacteria (Oenococcus oeni, Lactobacillus strains) and Brettanomyces produce acetic acid, but its presence as a flaw is generally attributed to Acetobacter aceti.

The detection threshold for acetic acid hovers around 0.7 g/l, and the US government enforces the following maximum acetic acid levels for wines:

Red wine: 1.40 g/l (1.70 g/l if Brix at harvest is 28° or higher)

White and Dessert Wines: 1.20 g/l (1.50 g/l if Brix at harvest is 28° or higher)

Source: 2013 Code of Federal Regulations

Ethyl Acetate

Ethyl acetate’s aroma of nail-polish remover typically accompanies—but is not necessarily an indicator of—volatile acidity. Ethyl acetate is an ester of acetic acid and ethanol, and has a much lower perception threshold than acetic acid. Acetic acid bacteria generate ethyl acetate, but other microorganisms may synthesize it as well; thus, it often appears hand-in-hand with volatile acidity, but the causes are distinct.

Oxidation

The oxidation of polyphenols in grape juice begins to occur the moment a grape skin is punctured or crushed, and leads to browning and aromatic changes in juice and wine. Following fermentation, ethanol, polyphenols, and other organic compounds may be oxidized in the presence of oxygen. Winemakers may add sulfur dioxide to juice prior to fermentation to protect it from oxidation—or rather to prevent the aromatic changes associated with oxidation—and may add it judiciously before bottling for the same reason. Some winemakers prefer to allow deliberate oxidation for white wines during crushing and pressing: the juice browns as phenolics in the must oxidize, but freshness returns during fermentation as these polymers drop out of suspension. This is widely practiced with Chardonnay and other barrel-fermented whites, as it protects against later in-bottle oxidation, but uncommon for varieties that are dependent on thiol and/or terpene aromas.

Varying levels of oxidation may also occur after fermentation in order to achieve a certain style. Sans soufre (“without sulfur”) methods, long aging in wood, regular bâtonnage and frequent racking lead to more pronounced oxidation in wines. The fortified wines of Sherry, Madeira, and Tawny styles of Port are highly oxidative in style, as is Jura’s Vin Jaune. In most cases, severe oxidation is considered a fault, affecting color and aroma. Severe oxidation conjures scents of bruised apple and walnut—aromas associated with acetaldehyde and sotolon, first- and second-generation products of the oxidation of ethanol, respectively. Fruit notes become muted, and the taster is left with an impression of flatness on the palate.

Maderization

When “maderization” is used to refer to anything other than the wines of Madeira, it indicates a fault linked to heat exposure, which speeds up the process of oxidation and leaves wines with a cooked flavor.

Sulfur

ETS-reported sensory thresholds for sulfur compounds.

Hydrogen sulfide (H2S) – 0.9-1.5 ppb

Ethyl Mercaptan (CH3CH2SH) – 1.1-1.8 ppb

Methyl Mercaptan (CH3 SH) – 1.5 ppb

Dimethyl Sulfide (CH3 SCH3) – 17-25 ppb

The most pungent, off-putting sulfurous aromas result from hydrogen sulfide, thioethers and thiols (mercaptans). Yeasts naturally generate hydrogen sulfide from sulfur-containing amino acids and other compounds in the fermenting must. Low levels of nitrogen in the must, sulfur dioxide (sulfite) additions, elemental sulfur residue on recently sprayed grapes, and even certain yeast strains promote the development of the highly volatile hydrogen sulfide, which imparts a rotten egg aroma to wines. Its formation during fermentation is predictable, and is corrected by aeration, or through the addition of the yeast nutrient diammonium phosphate (DAP), which prevents its accumulation. Regardless, most hydrogen sulfide dissipates alongside carbon dioxide. After fermentation, however, lees contact creates an environment favorable to reduction, and sulfur dioxide in the wine may be converted into hydrogen sulfide. Bâtonnage and racking diminish it, and judicious use of copper sulfate will remove it. Ultimately, the noticeable presence of hydrogen sulfide is always a fault in bottled wines, but it is easily preventable.
When conditions for hydrogen sulfide production are favorable, the wine is said to have low redox potential. In other words, the wine favors reduction over oxidation, and volatile sulfur-compounds like thiols and thioethers are more likely to appear. These frequently foul, putrid and highly pungent compounds are much more difficult to pry out of a wine than hydrogen sulfide. Simple aeration will not remove them. However, at low concentrations some of these volatile sulfur compounds can provide complexity, and certain thiols even create varietal signatures. Thiols, like hydrogen sulfide, are generated from sulfur-containing amino acids (principally cysteine) during fermentation. The rotten cabbage, burnt match odors of methyl mercaptan and the rubbery, rotten onion odors of ethyl mercaptan are unpleasant enough, but other thiols are responsible for the blackcurrant notes of Cabernet Sauvignon, or the passion fruit tones of Sauvignon Blanc. Dimethyl sulfide is the most common example of an odorous thioether. It likely arises from a degradation of cysteine, and can produce cabbage-like aromas in the wine. Dimethyl sulfide and diethyl sulfide can provoke similar scents. In general, thiols carry a much lower threshold for perception than thioethers.

Sulfur off-odors are a particular problem for screwcap-closed wines.

Impact Aromas

Wine aromatics result from numerous volatile flavor compounds; some are present in grapes and some are byproducts of fermentation and other winemaking processes. While there are hundreds of aromatic compounds in wine, most are insignificant on their own, appearing in concentrations well below human thresholds of perception. Classically, the most important contributors to wine aromatics are separated into two categories of compounds: impact compounds, which create distinctive varietal aromas, and the subtler contributing compounds, which add to overall complexity but do not provide distinguishing varietal character. However, recent studies challenge and complicate the classic approach to sensory perception. Vicente Ferreira, a leading researcher in wine flavor chemistry, offers three categories of aroma: impact compounds, impact groups, and contributory compounds (or groups). In addition, there is wine’s base aroma, a complex of 22 integrated compounds that form a general, perceptible vinous scent without any individual nuances. Ethanol, higher alcohols, acetic acid, and other compounds in acceptable concentrations for wine form the base aroma, and buffer other volatile odorants in the wine. According to Ferreira, the vinous “aroma buffer” can be broken by single aromatic molecules in large concentrations (impact compounds), by groups of nearly identical-smelling compounds in large concentrations (impact groups), or by subtle compounds which fail to transmit their own aromas but can contribute to the aromatic intensity of other, similar-smelling compounds (contributory compounds). In this sense, impact compounds and groups represent any molecules that directly convey their specific and unadulterated aromatic nuances in the finished wine. They may be varietal in origin (pyrazine in Cabernet Sauvignon)—or they may not (lactones in oak).

The best deductive blind tasters recognize impact aromas in wine and relate them to a wine’s structure and color in order to logically conclude grape identity and winemaking technique. Unfortunately, clear impact compounds that point neatly to one or a small handful of varieties are not common in wines. Additionally, most of the below impact compounds appear in many—if not all—Vitis vinifera grapes, and it is the relative concentration of an impact compound in a particular grape that becomes its signature.

Pyrazine

2-methoxy-3-isobutylpyrazine is an impact aroma closely associated with Cabernet Sauvignon, Cabernet Franc, Sauvignon Blanc, and other closely related Bordeaux varieties. Tasters attribute the vegetal scents of green bell pepper, asparagus and cut grass to the presence of pyrazine in wines. Pyrazines steadily decrease in the weeks following véraison. While pyrazines are most detectable in Bordeaux grapes, many varieties contain these compounds and may display a green fragrance, particularly if harvested under-ripe. Rarely, pyrazines can enter wines from an altogether different source—the orange Asian ladybug! In cases where Harmonia axyridis beetles slip into fermentation or aging vessels, they may secrete 2-isopropyl-3-methoxypyrazine into the wine. “Ladybug taint”—an off-flavor charitably described as “green” and less tolerantly as smelling like rancid peanut butter—seriously affected the 2004 vintage in Burgundy and the 2001 vintage in Ontario.

Monoterpenes

This family of related compounds is responsible for the highly aromatic, floral and sweet citrus notes of Muscat Blanc à Petits Grains, Gewürztraminer, Torrontes, Viognier, and (to a lesser extent) Riesling and Albariño. Terpenes are usually strong-smelling compounds—the word “terpene” is derived from “turpentine”—and white varieties given voice by sufficient monoterpene content are known as “aromatic” varieties. Monoterpenes accumulate during ripening. They are usually located in the grape skin and remain relatively unchanged by fermentation—a fresh Muscat grape tastes much like a Muscat wine, for example—but they tend to degrade or otherwise chemically rearrange quickly during bottle aging. Botrytis cinerea also tends to reduce monoterpene content; thus, Muscat is not usually a good candidate for noble rot. Some examples of monoterpenes include:

cis-rose oxide: The monoterpene responsible for Gewürztraminer’s unique rose and litchi aromatics has a very low threshold for detection, resulting in the grape’s incredible intensity of aroma.
Linalool: This slightly spicy, highly floral compound is, alongside geraniol (the scent of geraniums and lemon) and nerol (orange and rose), responsible for the intense fragrance of Muscat wines. Unlike most monoterpenes, linalool amasses in the grape’s flesh, not its skin, and therefore attains a high proportionate concentration in must.
Citronellol: During fermentation, certain yeast strains may form citronellol (dihydrogeraniol) through the reduction of geraniol. Citronellol gives a citronella candle its characteristic floral scent.
Alpha-terpeniol: A less aromatic monoterpene—linalool is 10 times as odorous—alpha-terpeniol transmits grapey, pine-like aromas. It is associated with lower-quality Torrontes wines from Argentina.

Rotundone

Rotundone is a sesquiterpene responsible for the highly peppery aroma of Syrah, Grüner Veltliner, Mourvèdre, and the Italian red varieties Schioppettino and Vespolina. It has a very low detection threshold—just a few parts per billion—but a sizable segment of the population is totally unable to smell the compound. Rotundone accumulates in the grape skin, and increases in concentration during the period from véraison to harvest.

Thiols

These sulfur-containing compounds are present as odorless precursors in ripe grapes. Unlike monoterpenes, they have no discernible flavor in fruit, because they are chemically bound to non-volatile substances like sugars or amino acids. During fermentation, however, yeasts metabolize sugar and amino acids, and render thiols volatile. Rising hydrogen sulfide levels in the fermenting must, light exposure, and high levels of heat can also lead to the generation of thiols. These compounds, also known as mercaptans, can be the source of rubbery, garlicky off-aromas in wine, but they also provide certain distinctive varietal aromas, such as grapefruit, blackcurrant, passion fruit, lemongrass and guava notes. They tend to increase in concentration during bottle aging. Thiols are incredibly pungent: ethanethiol, the source of rotten onion aromas in wine, is readily perceived at a concentration of under one part per billion. Many will recognize ethanethiol as the aroma of natural gas—companies add the thiol to the otherwise odorless substance as an alarm in case of leaks. Examples of thiols include:

4MMP: 4-mercapto-4-methyl-pentan-2-one is present in Cabernet Sauvignon and Sauvignon Blanc grapes. It lends the red grape its strong blackcurrant/cassis note, and provides the guava and “cat pee” aromas of the latter. 4MMP has also been identified in Scheurebe, Chenin Blanc, Riesling, Sémillon, Furmint, Merlot, and a handful of other grapes.
3MHA and 3MH (also called 3SHA and 3SH): 3-mercaptohexyl acetate (passion fruit and broom/box-tree aromas) and 3-mercaptohexan-1-ol (grapefruit and passion fruit aromas) are both present in high concentrations in many examples of Marlborough Sauvignon Blanc. According to The Handbook of Enology, “Gewürztraminer…may contain as much as 3200 mcg/l of 3MH, or over 50 times the perception threshold, whereas, in the case of geraniol, this ratio hardly ever exceeds two.” Spanish Verdejo is high in 3MHA and 3MH, and recent studies conducted by Denis Dubourdieu and others have demonstrated an incredibly high concentration of the latter compound in the botrytized wines of Sauternes.
2FM: Originally identified in roasted coffee, 2-furanmethanethiol (or furfuryl mercaptan) is less a varietal aroma than a signature of oak treatment. Furfural, a compound generated during the barrel toasting process, is converted by the metabolism of sulfur by yeast into 2FM, and lends a wine its characteristic scent of roasted coffee. It is more common in barrel-aged white wines than reds; it also develops during Champagne bottle aging, both before and after disgorgement.

Norisoprenoids

This class of volatile compounds results during ripening from the degradation of carotenoids, yellow- and orange-pigmented compounds occurring naturally in grapes and many other fruits. Sunlight intensifies their development. Volatile norisoprenoids generally appear in greater concentrations in red grapes, although they are present in all varieties. Unlike many aromatic compounds, norisoprenoids generally accumulate in the fruit’s pulp, not its skin.

Beta-damascenone: Compared to stewed apple, rose, and honey, this aromatic compound lends rose oil its distinctive scent. The unusually high concentrations of beta-damascenone in Chardonnay and Riesling grapes lead many to suggest that it plays a part in their varietal aromas. Its role as an impact compound in red wines, however, was challenged in a 2007 study conducted by Bénédicte Pineau, Denis Dubourdieu, and others; they concluded that its role in red wine aroma was indirect, possibly enhancing other aromas but not contributing its own. Ferreira lists beta-damascenone as an “aroma enhancer” for most wines—part of the base aroma that enhances fruity and sweet notes but generally unable to transmit its own.
Beta-ionone and Alpha-ionone: These compounds have a floral fragrance reminiscent of violets and raspberries, and likely bear some responsibility for these aromas in red wines. Several recent studies have shown that choice of yeast strain affects the retention of beta-ionone (and beta-damascenone) during fermentation.
Vitispirane: This norisoprenoid has an aroma reminiscent of chrysanthemums, eucalyptus or camphor, and is believed to accumulate during bottle aging. It is a signature component in Tawny Port.
TDN: 1,1,6-trimethyl-1,2-dihydronaphthalene is the compound associated with the petrol/kerosene smell in some Riesling wines. Research suggests that TDN attains higher concentrations in warm, sunny climates, yet it tends to develop in some northern European Riesling wines with age. Dr. Hans Schultz, Director of Geisenheim Research Institute, suggests that water stress, nitrogen deficiency, and the selection of yeast strain and clone impact TDN development in Riesling grapes. TDN is present in all wines, but it typically occurs at concentrations below the perception threshold, so petrol notes in wine are a strong indicator of the Riesling variety.

Isoamyl Acetate

Isoamyl acetate is an ester produced by yeasts during fermentation. At low concentrations, isoamyl acetate enhances fruitiness, but it delivers a clear banana/pear-drop note in greater amounts. Cold fermentation temperatures (59-68° F) enhance the synthesis and retention of isoamyl acetate. Isoamyl acetate has been associated with Pinotage, but it is generally a non-varietal aroma, appearing in many fruity, young white wines. It dissipates quickly with bottle age. It is a common aroma in German wheat beers, and the chemical is a chief flavoring for plain bubblegum. In red wines, the obvious presence of isoamyl acetate is linked with the process of carbonic maceration—which augments ester production—but some smaller growers in Beaujolais are challenging this view, retorting that a commercial yeast popularized in the 1970s and 1980s (71B) is instead to blame for banana flavors in the region’s wines.

Diacetyl

At the conclusion of malolactic fermentation, diacetyl accumulates in wine. While diacetyl is also a byproduct of primary fermentation, only during “malo” do its levels begin to surpass thresholds of perception. Diacetyl is responsible for slightly buttery, nutty notes in wine, and it is especially noticeable in white wines. It is one of the two compounds primarily responsible for the flavor of actual butter, and the chemical is used to flavor margarines and other artificial products. At high levels of impact, diacetyl is generally considered a fault.

Lactones (impact group)

As a type of ester, lactones are present in grapes; however, impactful lactones are usually the product of winemaking processes (fermentation or aging) or are derived from oak.

Sotolon: This lactone results from reactions between acetaldehyde and glutaric acid, and is a second-generation product of the oxidation of ethanol. In 1975, it was isolated as a chief component of fenugreek’s flavor, and it is responsible for notes of curry, maple syrup, and walnut in wine. It plays a role in the oxidative styles of Sherry, Vin Jaune, and Madeira; and it is also synthesized in grapes by the Botrytis cinerea fungus.
Whisky lactone: Technically known as cis-3-Methyl-4-octanolide (3S, 4S), the whisky lactone appears in wines aged in new oak. It was first identified as an aromatic compound in whiskey in 1970, and it has a sweet, woody, coconut-like fragrance. American oak barrels contain larger concentrations of whisky lactones than French barrels; hence, the smell of coconut is often associated with American oak barrel aging.

Dimethyl Sulfide

Dimethyl sulfide is part of a class of sulfur-containing compounds known as thioethers, and it is commonly considered a fault, smelling of cooked cabbage and shrimp at high concentrations in wine. However, at lower concentrations it imparts corn, black olive, and truffle notes, and plays a role in the bouquet of older Champagne and Chardonnay wines.

When blind-tasting, “a-ha!” wines that showcase one or two signature impact aromas (e.g. pyrazine in Cabernet Sauvignon, or linalool in Muscat) may be among the simplest to deduce, but they may lack complexity. Complexity may result from the suppression of clear impact aromas—i.e. a basic Torrontes may derive its floral aroma almost wholly from linalool, geraniol and terpeniol, but a more complex Riesling may derive its floral attributes from a constellation of impact compounds, including monoterpenes, vanillin, norisoprenoids, and thiols. For Riesling, the monoterpene concentration is less impactful, but the whole may have more complexity—a symphony instead of a single instrument.

Aroma Assessment

After determining whether a wine is sound, a sommelier should approach the nose in a methodological fashion; the Guild of Sommeliers recommends first assessing the aromatic intensity and age, then judging the wine’s fruit, secondary non-fruit aromas, earth aromas, and finally the imprint (or lack thereof) of oak. When blind-tasting, this framework provides a useful funnel for deductive reasoning: one first examines the imprint of variety and climate (fruit character and non-fruit character), before looking for the usage of winemaking techniques like barrel-aging.

Aromatic Intensity

After determining whether a wine is sound, a taster should gauge its aromatic intensity, or “volume.” Here, a taster is not ascribing any qualities to the type of aroma, but is merely determining how powerful it is. Wines rich in monoterpenes and thiols tend to be the most pronounced in aroma. In red wines, carbonic maceration promotes higher aromatic intensity.

Typical Examples of High Intensity: Gewürztraminer, Muscat Blanc à Petit Grains, Viognier, Torrontes, Marlborough Sauvignon Blanc, Beaujolais Nouveau, Sauternes

Typical Examples of Elevated Intensity: Albariño, Barolo, Carmenère, Mendoza Malbec, Zinfandel, Napa Valley Sauvignon Blanc, Young Vintage Port, Amarone della Valpolicella, Beaujolais Cru, Red Burgundy, Alsatian Pinot Gris, Grüner Veltliner, Sancerre

Typical Examples of Medium Intensity: Bordeaux Reds, Rioja, Chianti, Cornas, Italian Pinot Grigio, Chenin Blanc

Typical Examples of Diminished Intensity: Muscadet, Chablis, Young Hunter Semillon

Age Assessment

When nosing a wine, one gets a snapshot of its general age range from its intensity and the vibrancy of its fruit qualities. Most wines built for the cellar will lose aromatic intensity but gain aromatic complexity as they age. Obvious new oak aromatics integrate with age, and monoterpene concentration falls quickly during bottle aging. In young wines, fruit will be clear, direct, and primary; as wines age fruit fades and dries out, and more interesting secondary and tertiary non-fruit aromas develop—the wine gains its “bouquet.” Blind-tasting older wines can be very difficult as they shed the obvious varietal aromas of youth.

Fruit Descriptors

Wine is made from grapes, and all wines—even the earthiest, funkiest, dirtiest wines out there—should have some semblance of fruit. For beginning tasters, recognizing aromas suggestive of individual fruit types in wine can be a difficult exercise. Often, it is helpful to think broadly first—what category (or categories) of fruit does it show? White wines often display fruits in the citrus, pomaceous, stone/pit fruit, melon, and/or tropical categories. Red wine fruit categories include the spectrum of red, blue, and black fruits (both berries and tree fruits) as well as raisins and dried fruit. While there can be overlap—Grenache and Zinfandel may smell like apricot, and Riesling may smell like black currant or red cherry, for example—these categories provide a useful frame for most wines. Grape varieties often have individual fruit profiles: Viognier has a strong stone fruit character, whereas Chenin Blanc more likely exhibits sweet citrus and pomaceous (orchard) fruits. These categories are also a helpful indicator of climate. Dominant sour citrus points to a cool climate, whereas ripe tropical tones are more prominent in hot climes; for red wines cranberry and sour cherry implies a less ripe grape, whereas raisin or jam suggests heat and over-ripeness. Once a category has been chosen, hone in on a specific fruit: if the wine shows citrus, is it lemon, lime, orange, or something else? In all aspects of tasting, the sommelier can funnel from broad strokes to a fine point.

When describing fruit character, a taster should try to detail both type of fruit and its condition. For instance, “apple” is a pretty basic fruit descriptor for white wines, and could be applied to just about anything. However, “tart green apple” might signal a youthful, cool climate wine like Chablis or Sancerre, whereas “bruised apple” might indicate an oxidative white like Savennières, or even Fino Sherry. “Baked apple” may be more appropriate for Chardonnay produced in a warm climate. The actual type of apple—Fuji, Gravenstein, Jonathan, etc.—is just a flourish, and far less important than understanding the condition of its ripeness. (Unless you plan to write tasting notes for a living.)
Be precise, but don’t overcomplicate fruit. The more esoteric and poetic one becomes with descriptors, the less universal and helpful they are. Carambola, durian, cherimoya, and mangosteen might seem like thoughtful and impressive descriptors, but you are likely alienating your audience. One person’s lemon is not another’s lime—they simply do not smell the same—but do try to keep fruit descriptors basic, understandable, and as universal as possible.

Non-Fruit Descriptors

When a glass of wine delivers aromas beyond the simple scents of fruit, things get interesting. Non-fruit aromas in wine have the power to evoke childhood imagery and lead to creative association. Wine’s capacity to toggle memory raises it above the category of mere drink, but a taster’s duty (in this sense) is to universal language rather than internal observations; so, “This wine smells just like grandma’s perfume!” is not doing anyone any good. Actually, maybe that one is universal.

As with other components of tasting, it is advisable to approach non-fruit aromas consistently. They are rungs on a ladder. Some aromas, like flowers, are more delicate and may be submerged under the heavier aromas of oak or spice; failing to look for these fleeting aromatics and immediately latching on to more obvious tones results in an incomplete picture of the wine. A tasting grid, or mental checklist, offers obvious advantages here as it forces the taster to examine every possible realm of non-fruit aromas, rather than simply cataloging the loudest notes. For example, imagine a white wine that tastes and smells of lavish, toasty new oak. A beginning taster may swerve toward the obvious oak, and jump to a conclusion—“Chardonnay!”—without considering other equally valid varieties like Viognier or Sauvignon Blanc. Checking for lighter floral and herbal aromas would provide a clearer picture of the wine, even if oak remains dominant. In the case of certain impact compounds (pyrazines, monoterpenes, rotundone, thiols), non-fruit aromas provide important varietal clues; other non-fruit aromas can be attributed to oak or winemaking techniques. When blind tasting, remember that winemaking aromas are like circumstantial evidence in a courtroom: a malolactic-derived aroma in a white wine certainly builds a case for Chardonnay but it will not win a conviction alone.

Sometimes, it is helpful to think of non-fruit categories as binary rather than scalar propositions. For example, a taster could view floral aromas as a scale or spectrum, ranging from “no flowers” to “extremely floral,” and encompassing every frequency (slight white floral aromas, citrus blossoms, etc.) along the way. Tasters who approach floral aromas in this way may form a more aromatically complete description of a white wine (inevitably mentioning white flowers, or some blossom matching the fruit notes previously recorded), but the description may be of less help in the final deduction. A binary approach—is a wine floral, or is it not—might lead to a better deduction. In this case, considering floral aromas in a white wine as an either-or proposition could lead to a very clear deduction: is the wine likely produced from a variety with a higher concentration of monoterpenes, or is it not?

The basic categories of non-fruit descriptors are as follows:

Floral Aromas
Herbal Aromas
Vegetal Aromas
Spice Aromas
Other Non-Fruit Aromas
Earth/Mineral Aromas
Botrytis Aromas: Honey, Saffron, Ginger, Dried Apricot
Malolactic Aromas: Sour Cream, Butter, Yogurt
Sur Lie Aromas: Cheese, Marshmallow, Vanilla
Oak Aromas: Toast, Vanilla, Baking Spices, Coffee, Caramel, Maple, Smoke (see "Oak Aromas" section below)

Earth and Minerality

Minerality, on the nose or palate, is a hotly debated topic. Do wines really taste or smell of granite or limestone? Not likely. However, they may display certain characters that remind a taster of soil or rock: tannins may feel gravelly or heavy like wet clay, or a white wine might smell like wet stones or upturned river rocks. The latter is petrichor (the “scent of rain”), but unlikely to be the innate smell of a stone; the former is a figurative expression for a tactile sensation. Former geologist and long-standing Master Sommelier Wayne Belding offers the following perspective:

I think many students get overwrought trying to define "minerality" more precisely than is possible. Rocks and minerals are actually two separate entities, but that's another discussion. I have heard all sorts of descriptors - from limestone and granite to sandstone, red sandstone, hot red clay, and many more. It becomes meaningless. You can line up (and I have) samples of limestone, granite, basalt and whatever other rocks you choose and smell them - there will be no difference. You can lick them (I have done that as well) and they taste the same. It's clearly not the aroma and/or flavor of the rocks that humans can perceive. That said, there is a distinctive scent of seashell or chalk dust in some examples of Chablis. So too, there is a consistent character of Mosel Rieslings that we sometimes call "slate" in recognition that the wine was drawn from slate-based soils. Since we can smell and taste slate from the Mosel and not find any distinctive character in that exercise, we must logically conclude that the distinctive scent has some other origin. It becomes a sort of circular reasoning - we think the wine is from the Mosel, so we call it “slaty,” more as an affirmation of our imminent conclusion than a direct sense of a rock type. So it is with limestone, basalt, granite and other rocks. We associate familiar wine characteristics with those terms based on our knowledge of the soils from which they are drawn.

I encourage students to develop an earthiness vocabulary that covers inorganic and organic expressions of earth. “Inorganic” can encompass terms like wet stone, dusty, graphite, seashell and chalk, because we can pick up seashells, chalk, etc., smell them, and perceive a distinctive aroma. To go beyond that - declarations of limestone, sandstone, etc. - gets a bit precious for me. It is not as much a description as it is an initial conclusion. “Organic” earth is a broader and somewhat more precise category. We can find mushroom, forest floor, barnyard, compost, potting soil, tobacco and beyond in wines because we can smell those entities and develop an olfactory memory of them.

Alex Maltman, (Institute of Geology and Earth Sciences, University of Wales at Aberystwyth) is even more blunt:

Attempts to explain the perception of minerality involve allusions to geological materials, these are irrelevant to its origin.
Whatever minerality is, it cannot literally be the taste of minerals derived from the vineyard geology.

So what is it? Reductive and sulfide aromas in wine are commonly cited as “mineral,” and there are German studies linking “mineral” perception in wines with higher levels of acidity. Some earthy aromas result from spoilage yeasts like Brettanomyces. At the end of the day, “mineral” and “earth” are figurative tasting terms, best used to conjure association, rather than direct and literal descriptors for the taste of a particular soil or rock.

Oak Assessment

A new, toasted oak barrel may imbue scents of vanilla, baking spices, grilled toast, smoke, caramel, and other tones in a wine during the maturation process. Oak wood contains three compounds chiefly responsible for these aromas: hemicellulose (a wood sugar), oak lactones, and lignins, which bind fibrous cellulose matter in the plant into hard wood. Hemicellulose sugars caramelize during toasting and result in the formation of furfural, which contributes an almond- and caramel-like aroma; furthermore, furfural can be converted by yeast into the thiol 2FM, with its characteristic aroma of roasted coffee. Oak lactones, derived from lipids in seasoned wood, are responsible for fruity, coconut, and fresh wood scents in wine. There are two principal oak lactones, the whisky lactone (or cis-oak lactone) and the trans-oak lactone; the former is present in much higher concentrations in American oak. Lignins react with ethanol during the aging process, break down, and eventually oxidize, resulting in aldehydic compounds like vanillin and coniferaldehyde, and phenolic alcohols like eugenol and guaiacol. These lignin-breakdown products create many of the sweet, spicy and woody aromas that tasters associate with wines aged in oak. Vanilla character tends to be less prominent in light-toast barrels, and more prominent in medium and medium-plus toast barrels. At heavy toast levels, it (along with other lignin-breakdown aromatic products) recedes in favor of smoke, clove, and char. Oak lactones, on the other hand, are most prominent at light toast levels, as high heat destroys them outright.

In addition to its effects on aroma and flavor, oak maturation allows slight oxidation of the wine over time, as wood is porous and permeable to gas. Wood porosity accounts for subtle variations in oxygen ingress: more porous woods of French oak species permit a greater exchange than less porous woods of American oak species. (It is useful to remember that tight-grained oak is more porous than coarse-grained oak!) Age of the wood and thickness of the staves also impact the rate at which oxygen dissolves in wine. The age of a barrel is also a factor: older oak, soaked with wine, permits less oxygen ingress than a brand new barrel. Additionally, racking and other handling procedures create a sudden and much greater transfer of oxygen than the limited, gradual ingress that occurs through the staves themselves. Once oxygen dissolves in wine, various compounds begin to oxidize in its presence; in addition to changes in color and structure, aromas of “reduction” are lost and pure, intense fruit notes tend to be slightly suppressed.

The effects of oak aging on a wine are more noticeable when a winemaker employs smaller vessels, such as the 225-liter Bordeaux barrique, and uses new oak. The amount of wine-to-barrel surface area decreases dramatically from a large European cask of 1200 liters or more to a small barrel one-fifth its size, and the inference of oak becomes more obvious. And whatever its size, an oak barrel or cask only has a finite amount of volatile compounds and non-volatile polyphenols to contribute to wine. Wine’s ability to extract flavor, body, and tannin from an oak barrel decreases significantly after the barrel’s first fill, rendering it neutral (in tasting parlance) over several vintages. Typically, a French barrel may be effectively neutral by its fifth fill, whereas an American barrel may continue to provide aromatic character and tannin through its seventh or eighth fill. A taster should be able to discern the effects of subtle oxidation on the nose in any wine that has undergone significant barrel maturation, but the aromas of oak will be most prominent in wines that see new barrels.

While sommeliers are almost universally successful in identifying new oak in white wines, they typically overestimate its presence in reds. Save for high-end bottlings of Bordeaux and Burgundy varieties, and full-bodied, fruit-driven New World wines such as Zinfandel, new oak usage is an uncommon and expensive endeavor for the world's traditional wines. Understanding the precise aromas imparted by a $1300 new oak barrel is tremendously helpful in deductive tasting. A classified growth Bordeaux and a traditionally produced Brunello di Montalcino should never be confused on this basis.
–Geoff Kruth MS

The Palate

Most tasters approach the palate after thoroughly examining the nose of the wine, although some advocate taking a cursory sip of the wine at the beginning of the tasting assessment, in order to quickly gauge major structural factors, like residual sugar. Fatigue can build on the palate just as it does on the nose, and structural components like tannin and acid tend to build in strength as one tastes more and more tannic and/or acidic wine. Try to ascertain as much as possible about the palate of the wine from just one or two sips, and remember that bitterness, tannic astringency and the warmth of alcohol will take a few seconds to register on the palate, whereas sweetness is fairly instantaneous, and acid appears not long thereafter. While recognizing that everyone is different, we list the elements of the palate below in the order that we recommend assessing them.

Sweetness

Sweetness refers to the presence of unfermented residual sugars in the wine, rather than the suggestion of sweet flavors, like ripe fruits. Sweetness should be gauged immediately, before other structural elements emerge to influence its impression: acid tension can balance and distort residual sugar on the palate, and high levels of alcohol tend to exaggerate sweetness. Carbon dioxide in sparkling wines suppresses sweetness. At least one sweet-tasting compound (quercotriterpenoside) is released from wood into wine during new oak aging, and the vanilla-laced aromas of new oak can appear misleadingly sweet as well. On the other hand, significant reductions in acidity, bitterness, or astringency in wine can artificially inflate perception of sweetness. True sweetness reveals itself almost instantaneously and dissipates more quickly than acidity, so log it first, and trust your initial impression.

Sugars in a fully ripened grape are the dominant soluble solid, capable of reaching concentrations of 200-250 g/l (20-25%) or more. Of course, for most wines the bulk of sugar is metabolized to produce ethanol during fermentation, but for naturally sweet wines some unfermented, residual sugar remains. V. vinifera grapes accumulate two main sugars, glucose and fructose, as they ripen. While the ratio of the two sugars varies by variety, fructose steadily increases in proportion as the grape advances toward harvest. Fructose is nearly twice as sweet as glucose, and is perceived sooner on the palate. It also ferments more slowly; thus, naturally sweet wines tend to have an even higher balance of fructose, and—all other things being equal—will taste slightly sweeter than those made with süssreserve or sparkling wines with a sucrose dosage.

Wines without noticeable sweetness are termed “dry,” and those that are exceedingly so are often called “bone dry”—although wines are usually only catalogued as the latter when they are both dry (not sweet) and drying (tannic), or dry and incredibly acidic. All wines, even those that appear unforgivingly dry, have at least some small amount of remaining sugar. Most truly dry red wines fall between 0-2 g/l. (Distinguishing between “dry” at 2 g/l and “bone dry” at something closer to 0 g/l is generally not possible, as gustatory perception thresholds for sugar hover near 2 g/l for the most sensitive tasters, and the majority of people require more than 10 g/l before noticing sugar in wine.) Dry white and rosé wines, with their more robust acid levels, tend to land somewhere between 0-4 g/l, although “dry” Vouvray and German Riesling may reach 9 g/l. Such wines may be legally dry, but a pillow of sweetness is usually noticeable, and should be indicated. This could even provide an important blind tasting clue—Australian dry Riesling, for instance, is usually in the 0-3 g/l range while many German trocken styles have 5-9 g/l. Attention to detail at this low level of residual sugar allows a taster to register the presence of dosage in sparkling wines, which often falls in the neighborhood of 8-10 g/l. Whatever the legal language allows, any wine with perceptible sweetness in excess of 4-5 g/l should be deemed “off-dry.”

The following ranges of sweetness provide useful, universal intervals for tasting, but they do not necessarily correspond to any legal definitions.

Dry: 0-5 g/l (0-0.5%)
Off-Dry: 5-20 g/l (0.5-2%)
Medium Dry: 20-60 g/l (2-6%)
Medium Sweet: 60-125 g/l (6-12.5%)
Sweet: 125-175 g/l (12.5-17.5%)
Luscious: +175 g/l (+17.5%)

As sweet wines age in the bottle, we may record impressions of reduced sweetness, but the wine’s actual residual sugar level does not change over time. In sweet table wines and sparkling wines with dosage, sugar caramelization and Maillard reactions between sugars and amino acids may be responsible for altered perception of sugar and toasty aromas, as well as contributing to the browning of wine color.

Flavor

Flavors captured on the palate are simply aromas experienced retronasally. While some systems of tasting suggest that aromas should be reiterated (i.e. “confirmed”) on the palate, this may not be necessary from a deductive perspective. Flavors may change in character, however, and this is usually in tandem with some element of structure. For instance, fruit aromas suggestive of ripeness may tighten and seem tarter on the palate, offering a clue that the wine likely has heightened acidity. Mint on the nose may turn to menthol on the palate in conjunction with high alcohol. New flavors may appear, or subtle aromas may become obvious flavors. In any case, flavor assessments that continue to advance a description of the wine are useful; those that simply retread old ground are not.

Body

The body of a wine lies in its perceived weight upon the palate, and it is primarily a function of the wine’s viscosity and level of dry extract. Viscosity—not to be confused with tearing—is higher (“thicker”) in wines with higher alcohol content and/or high levels of residual sugar, so alcohol and sugar lend a feeling of weight to a wine. Low-alcohol wines tend to be light-bodied, and high-alcohol wines tend to be full-bodied. Luscious sweet wines are likewise full-bodied, regardless of alcohol level. Residual sugar increases a wine’s viscosity, and it also raises the wine’s total level of dry extract. Total dry extract is the sum of all dissolved solids in a wine: residual sugar, tannin and other polyphenols, fixed acids, glycerol and traces of minerals and other substances. All of these components can add weight to a wine. New oak aging—a contributor to dry extract—also adds body to a wine, and sur lie aging, particularly with regular bâtonnage, can add a feeling of fullness to wine.

To assess body, an analogy with milk is helpful: light-bodied wines have a watery, thin palate presence similar to skim milk, and full-bodied wines are mouth-coating and heavy, more akin to the feeling of half-and-half or heavy cream. In general, red wines tend to be heavier than white wines, but light-bodied reds and full-bodied whites both occur. Body tends to diminish with extended bottle age, although some white wines do seem to increase in body with time in the cellar.

Acidity

Acidity—sourness—is usually the second taste to manifest, and should be assessed after sweetness. Acid lends a refreshing, crisp undercurrent to wine, and unlike tannin, which dries the mouth out, acidity actually causes our mouth to water. As we drink wine or other acidic beverages, the pH in our mouths drops; when the strength of acidity on the palate threatens to dissolve tooth enamel, saliva comes to our defense by diluting the acid and raising pH to a more neutral level. The sharper and more acidic the wine, the more we salivate. So, one can gauge acidity by focusing on salivation, and noting the prickling, puckering sensation along the sides of the tongue that accompanies it.

No structural component in wine exists in a vacuum, and our perception of acidity can be influenced by other factors in the wine. Acid’s sheer force is blunted by sweetness (consider lemon juice vs. lemonade). While shrill, high acid wines easily mask a few grams per liter of residual sugar, significant sweetness can likewise prevent a taster from getting a good reading on acid. Most serious sweet wines tend to have higher levels of acidity; without it, a spoonful of residual sugar becomes cloying and lumpy on the palate. High levels of acidity can, perhaps counter-intuitively, heighten our impression of astringency as well. Finally, the notion of minerality in wine may be linked to acidity—even synonymous with it. High-acid wines are often tagged as “mineral,” while those with lower acidity are not. Sommeliers and scientists will continue to tendentiously debate this point, and partisans on both sides will remain undeterred.

Tartaric acid is the most important acid in wine; and tartaric, malic, and citric acids are the most common fixed (non-volatile) acids in grapes. Tartaric and malic acids comprise up to 90% or more of a grape’s total acidity, and they increase in quantity prior to véraison. From the onset of ripening the quantity of tartaric acid remains relatively stable—although tartaric acidity may decrease in proportion as the grape grows in size—while malic acid declines during plant respiration after véraison. By harvest much of the grape’s malic acid will have been consumed, particularly in warmer climates, and tartaric acid will form the dominant expression of acidity in the wine. Lactic acid, while not actually present in the grape, often appears in finished wines as well, as remaining malic acids are converted into lactic acids through malolactic fermentation. Astute tasters claim to distinguish between different types of acid on the palate; for instance, malic—from the Latin malus, or “apple”—may taste fresh, and as puckering and green as a sour apple, whereas lactic acid tastes soft and slightly sour, reminiscent of the tang of sour cream. The taste of tartaric acid is often described as hard or vinous, and the latter descriptor may be ideal—grapes are one of the few fruits in which tartaric acids appear in any appreciable quantity. Of course, scientific tests have not yet born out this anecdotal assertion: in controlled experiments, solutions of these acids in water taste only of, unsurprisingly, acid.

pH and TA

Three measurements of acidity offer a window on perception: total acidity, titratable acidity, and pH. Total acidity refers to the sum of a wine’s organic acids, chiefly tartaric, malic, and citric. Today, wines typically fall between extremes of 4.5 g/l (the minimum level permitted for wines in the EU) and 9 g/l, and total acidity numbers offer a preview of acid’s impact on the palate. Titratable acidity, on the other hand, approximates total acidity but is easier to measure and is always a smaller value—measurement of titration is affected by cations, such as potassium, which can “buffer” acidity. Both of these measurements are confusingly abbreviated “TA,” and are often incorrectly used synonymously. And while both measurements express (or attempt to express) a wine’s total acid content, results are usually provided in terms of grams per liter of tartaric acid equivalents. In other words, for the purposes of measurement, all acids present are assumed to be tartaric. TA is ultimately a measure of the quantity of acid in a wine, whereas pH determines an acid’s strength. pH values range from 0 to 14, and values below 7 (neutral, pure water) are increasingly acidic. pH is a logarithmic scale, so a liquid with a pH of 5 is ten times more acidic than a liquid with a pH of 6. White wines typically range from 2.9-3.5 pH; reds typically range from 3.3-3.8 pH. Different types of acid have different pH values as well: tartaric is a stronger acid than malic, and malic is a stronger acid than lactic. Although low pH wines generally have higher total acidity, and vice versa, the two values do not directly correlate. pH may measure the strength of acid, but TA appears to be a better predictor for the taste of acid.

Classically, we assume that cooler climates produce wines with higher acidity and warmer climvates produce wines with lower acidity. Although this is a truism—riper fruits are less sour—understanding its mechanism requires a look at plant respiration.

The process of respiration allows a plant to convert sugars produced through photosynthesis into energy. Grapevine leaves photosynthesize sucrose sugars, which move via translocation to the roots, shoots, fruit, and other areas of the vine. Prior to véraison, grapes intake sucrose but store little of it, preferring to convert the carbohydrate into energy through respiration. At the onset of ripening and color change, however, grapes replace sugar with malic acid as the fuel source for respiration, and the berries accumulate sucrose, which is broken down by the enzyme invertase into the simpler sugars glucose and fructose. Small increases in sugar content after véraison do result directly from gluconeogenesis—a direct conversion of excess malic acid to glucose—but in general the depletion of malic acid during ripening occurs in tandem with an increased accumulation of sugar. The sugar is stored, rather than used for fuel.

The rate of respiration is dependent on temperature: higher temperatures increase respiration while lower temperatures curtail it. In warmer climates, the rate of malic acid respiration increases, resulting in lower acidity in both grape and wine. When wine marketers presume significant diurnal temperature variation as indivisible from wine quality, this is the core of the argument: respiration occurs in the absence of light, but it is dependent on heat. Malic acid respiration slows with cool nights, yet the production of sugar during photosynthesis, while affected by temperature, can only occur during the day, in the active presence of light. Somewhat equally, warm regions with low nighttime temperatures (Ribera del Duero, Napa Valley) and cooler regions with sunny growing seasons (Alsace, Pfalz) can retain acidity while still accumulating sugar. The length of the growing season and harvest date, are major factors in the acid/sugar balance as well: new sugars produced by photosynthesis after véraison are not respired but translocated into the grape—the longer one waits to harvest, the more sugar will accumulate and malic acid will respire.

The simple theoretical truth of climate as fulcrum for the seesaw of acid and sugar is muddied, somewhat, by what actually occurs in the vineyard and winery. Warm climates usually produce lower-acid and higher-sugar (and therefore higher-alcohol) wines, but not always. An early-picked variety in a hot region, such as Hunter Semillon, will not support a warm climate conclusion. Any number of vineyard practices, from trellising systems to green harvesting to leaf removal, can complicate the picture. In the winery low acid levels can be corrected with the addition of tartaric acid, just as low sugar levels can be corrected with chaptalization. Potassium-rich soils tend to reduce acidity, as potassium collects in grape skins and precipitates with tartaric acid during skin contact. Both skins and stems have the ability to absorb tartaric acid, so longer macerations dampen acidity. The variables impacting acid structure are numerous. But when building a case for the identity of a wine it is always preferable to base deductions on rules rather than exceptions, and the relationship between climate and acidity remains a valid rule. What is not a valid rule is the outdated suggestion that Old World wines will necessarily have higher acidity than their New World counterparts. Acid is dependent on variety, climate, and technique—but it is not a function of geographic location.

During lengthy bottle aging, tartaric acids react with ethanol to form ethyl acid tartrates, and the sensation of acidity is rounded and diminished. Once a wine is over the hill, it begins to appear sharply acidic anew as the wine’s fruit and body disappear.

Tannin and Phenolic Bitterness

“Tannin” is a complicated subject, despite confident use of the term among wine tasters amateur and veteran alike. Ronald Jackson, author of Wine Science: Principles and Applications, defines tannins as: “phenolic compounds that can tan (precipitate proteins) in leather; in wine they contribute to bitter and astringent sensations, promote color stability, and are potent antioxidants.” Tannins exist in fruit, flowers, and green and woody matter throughout the plant kingdom, and their astringent taste is a defensive mechanism, warding animals from under-ripe fruits, leaves, and bark. Therefore tannins can enter a wine through maceration with grape skins, seeds, and stems; or from aging in oak barrels. Clearly they play a much more significant role in red wines; most white wines have little if any tannic imprint. Put simply, tannins are the element of a red wine’s structure that leaves the mouth with a drying impression. Tannins are felt, provoking astringency: this drying-out, rough sensation. Imagine a mouthful of cotton balls, or sandpaper on the tongue. The key function of tannins—their preference to form polymer chains with proteins—is the culprit here, as tannins bind with proteins in saliva, precipitating out of solution and literally robbing the mouth of moisture. Bitterness, on the other hand, is a taste. From phenolic sources we experience bitterness on the back of the tongue, and typically taste it after impressions of sweetness and sourness. Bitter tastes accompany all polyphenols in wine, but astringency is the more prominent feature of tannin.

Complications arise as tannins are not a single compound; rather, tannins are a class of polyphenols defined by their role: an ability to bind with proteins. In order to understand tannins a little better, let’s take a look at phenols and polyphenols first.

At a basic chemical level, a phenol is an organic compound consisting of a ring-shaped hydrocarbon molecule (benzene) bonded to a hydroxl (hydrogen and oxygen) molecule. It is slightly acidic and toxic on its own. Polyphenols, of more interest to the student of wine, are generally water-soluble compounds composed of multiple phenol groups. Additionally, phenols (or polyphenols) can be broadly divided into two groups: flavonoids and non-flavonoids. Flavonoids, a large class of antioxidant compounds, are key: this category includes anthocyanins, flavanols (like catechin and epicatechin), and procyanidins—polymers of multiple flavanols that are better known as condensed tannins. These condensed tannins are derived from grape skins and seed coats, and are principally the result of polymers of the flavanols epicatechin and catechin. In fact, it is catechin, found in grape seeds rather than ripe skins, that gives tannin its bitterness. (It is also the principal culprit in tea.) Non-flavonoids, also known as phenolic acids, include a second category of tannins, the hydrolysable tannins. This type of tannin is a polyphenol that includes a carbohydrate molecule, and therefore arises in bark and woody portions of plants. Not surprisingly, hydrolysable tannins arrive in wine mainly through aging in oak barrels. Hydrolysable tannins are related to gallic and ellagic acids in wood; however, “tannic acid,” oft-cited as a general synonym for tannin, does not occur naturally in wine (although it may be added by a winemaker for purposes of clarification or mouthfeel, or introduced through oak aging).

So, oak tannins (hydrolysable) and grape tannins (condensed) are different types of compounds, deriving from different parts of the plant. Some tasters are adept at distinguishing between the two on the palate: oak tannins tend to be less astringent, as they are generally ineffective at binding proteins in saliva, and grape tannins are quite drying in comparison. Grape tannins also show higher degrees of bitterness than oak tannins. Oak tannins pervade the palate and are more striking on the finish, whereas grape tannins live in the front of the mouth. Over time, aging joins oak and grape tannins in sensory impact. We advise most tasters to concentrate on the cumulative affect of tannins, rather than the separate impacts of oak and grape tannins.

The number of adjectives that can characterize tannins is nearly limitless: green, powdery, ripe, bitter, astringent, hard, coarse, fine-grained, stalky, rough, soft, etc. Some tasters and winemakers prefer to examine tannins’ “shape”: is the impression of tannin on the palate shaped like a horseshoe, a ring, or does it simply stripe down the tongue? For a sommelier, we recommend keeping it simple, and grading tannin in a red wine based on the force and length of astringency: diminished, moderate, elevated, or high. In addition, one can gauge phenolic bitterness, which to some degree accompanies tannin. Citing the presence of phenolic bitterness in a red wine, alongside tannin, may indicate a cooler vintage or under-ripe grapes (or at least not “phonologically ripe” grapes), a preponderance of grape (rather than oak) tannins, or a long length of maceration that favors greater extraction of bitter seed tannins. Higher alcohol levels increase the impact of bitterness; heightened acidity has no effect on bitter taste perception but it does increase the feeling of astringency. Does climate have an impact on tannin? Warm-climate, riper wines often appear less gritty and astringent than cooler climate versions of the same varieties, but overall tannin levels in the grape remain stable after véraison. However, with extreme ripeness and lignification (hardening and browning of seeds and stems), some tannins oxidize and bind to the seed coat, and become difficult to extract into the finished wine.

If this were the whole story, it would be challenging enough. But tannins have the maddeningly ability to change, polymerize, and break down in wine, and perception shifts with these transformations. Tannins in finished wine may not resemble tannins in grapes on a chemical level, and as wine develops tannins continue to alter in structure. Classically, wine educators have taught that tannins polymerize into longer and longer molecule chains, until they eventually fall out of suspension as sediment, softening mature wines. It has also been suspected that longer-chain tannins are less astringent than shorter-chain tannins, as the largest condensed tannins have apparent difficulty combining with proteins in saliva and reacting with taste receptors on the tongue. But new research is calling these sacred cows of tannin theory into question.

In the fermenting must, catechins (flavanols) and procyanidins (condensed tannins) begin to polymerize with themselves, forming larger condensed tannins than those existing in the grape itself. They also polymerize with anthocyanins, forming pigmented tannins, a key ingredient in long-term color stability. So far so good. But tannins do not simply combine into larger and larger compounds, they break apart as well, and recombine with themselves and other compounds, and generally behave in ways we currently struggle to understand. Douglas Adams, a specialist in grapevine physiology at UC Davis, describes the anarchy of tannin development during fermentation as a “chemical train wreck,” and wine journalist Tim Patterson alludes to a new quantum theory, supplanting the conventional “standard model” of tannins (Patterson, T. 2009. Everything You Know About Tannin Is Wrong. Wines and Vines.). Tannins do not simply form longer and longer chains, in fermentation and with age, and furthermore larger tannin compounds may actually be more astringent—not less. There is even a question about whether or not tannins may actually depolymerize with age, or at least remain in solution. Wines clearly soften with age, but the scientific rationale behind the phenomenon is currently under renewed study.

White wines, in general, have far less phenolic content than reds, and little if any appreciable tannin. However, white grapes and red grapes are quite similar in phenolic makeup, save for the greater presence of anthocyanins in red grapes. Skin contact and maceration during fermentation are chiefly responsible for drawing these compounds into the actual wine. Some polyphenols, like anthocyanin, are easily water-soluble and are readily extracted with techniques like pre-fermentation cold maceration; others, like condensed tannins, require higher temperatures or an ethanol solution before they can be extracted from skins and seeds. However, maceration over time is not the only means of extracting phenols—the simple acts of crushing or pressing grapes will also allow for some phenolic extraction, and adding sulfur dioxide to settling juice intensifies this effect. Extraction can begin in the vineyard, if grape skins are ruptured by clumsy mechanical harvesting or crushed in oversized containers. So even white wines may show phenolic character—bitterness and/or astringency—from periods of skin contact and cold soaking, crushing, or pressing processes. As in reds, both flavonoid and non-flavonoid polyphenols occur in white wines. According to a recent study by the Australian Wine Research Institute (Identification of the Major Drivers of ‘Phenolic’ Taste in White Wines, 2012), key non-flavonoids in white wines include hydroxybenzoic and hydroxycinnamic acids, and flavonoids include many of the same cast of characters appearing in reds, such as the flavanols catechin and epicatechin. The study’s authors report that catechin is, while bitter, not technically astringent, and that the human threshold for the detection of catechin and similar flavanols is low. A yeast-generated phenol, tyrosol, may also play some role in bitterness in white wines. White wines can therefore present phenolic bitterness without being actually tannic. Of course, barrel aging can contribute hydrolysable tannins to white wines, and lavish whites aged in new oak often have a low but perceptible level of tannin. “Orange” wines that undergo maceration through fermentation will also show noticeable levels of condensed tannin. On the other hand, with squeaky clean winemaking and modern techniques like whole-bunch pressing, phenolic content in white wines can be minimized.

It is important to note that white wines characterized by lower levels of acid often have increased levels of phenolics, as these bitter compounds balance and preserve the wine. Marsanne, Viognier, and Gewürztraminer all show prominent bitterness, compounded by regularly higher alcohol levels. Whites with higher acid can display phenolic bitterness as well: Albariño, Pinot Gris, Grüner Veltliner, and Fiano, for example, all tend toward slight bitterness. For a taster, it is paramount to distinguish between sourness and bitterness—two tastes that untrained tasters confuse frequently.

Alcohol

Ethanol (ethyl alcohol), a byproduct of fermentation, is the dominant alcohol in wine. It contributes to the wine’s weight, modifies perception of other structural components, and protects and stabilizes wine during aging. Under normal circumstances, S. cerevisiae may produce up to 15% ethanol; above that concentration, the environment turns toxic and most standard strains of yeast will die. Other alcohols do appear: methanol exists in low concentrations in wine but plays no direct role in taste, whereas fusel alcohols contribute to the wine’s base vinous aroma and its bottle bouquet by reacting with acids during the aging process. Sugar alcohols, including glycerol, are present in wine and may impact body (see below), but they do not have the intoxicating effect of ethanol. Ultimately the “alcohol by volume” measurement listed on all bottles of wine is solely a measure of ethanol.

Ethanol is a volatile, slightly sweet-tasting substance. In its purest form, it is essentially odorless, yet it acts as a nasal irritant, and high alcohol in wines may be perceived with a sharp sniff or two. Extreme levels of high and low alcohol may also be predicted by examining a wine’s tearing. However, the best method for determining the level of alcohol in wines is on the palate: alcohol creates a sensation of heat on the back of the palate and in the throat, and higher levels of alcohol create a sensation of warming in the chest. High levels of alcohol in wine enhance sweetness and bitterness, but suppress acid and astringency. As with other aspects of structure, every taster has his or her own sensory gauge of alcoholic strength; the key is to adjust one’s own impressions of heat (or lack thereof) to a universal scale. Alcohol, unlike acid or tannin, is clearly stated on all wine labels and one can make adjustments as necessary. But numbers can lie: in the USA, for instance, labels for wines under 14% abv can legally vary by up to 1.5% from the stated alcohol, and those over 14% can vary by up to 1%. Rather than attempting to estimate the exact percentage, we suggest placing alcohol on a scale: low, diminished, moderate, elevated, high. 30 or 40 years ago, “moderate” may have included wines as low as 10.5-11%, but the scale has shifted, as today’s viticultural techniques and climates have enabled riper wines and higher alcohol levels than ever before. Today, “moderate” alcohol should reflect the level routinely achievable without chaptalization in moderate winemaking climates throughout the world.

Low alcohol: This category includes any wines with less than 10% abv. For alcohol to be this low, there must be a winemaking explanation, such as halting fermentation to preserve residual sugar, or alcohol reduction technologies employed to create “low calorie” and lighter-styled wines currently in fashion.
Diminished alcohol: 10-12.4% abv. Wines with diminished alcohol levels generally result from cool climates or early harvests. Certain semisweet and sweet styles of wine will also fall into this category.
Moderate alcohol: 12.5-13.9% abv. This range represents most moderate-climate wines produced today throughout both the Old and New World, and also encompasses cool-climate wines produced on superior sites.
Elevated alcohol: 14-14.9% abv. Wines with elevated alcohol levels typically result from warm climates, superior vineyard sites in moderate climates, or late harvests.
High alcohol: 15%+ abv. There must be a winemaking/viticultural explanation for this level of alcohol. For instance, the wine may be fortified, or it may be the product of a late harvest or dried grapes.

Glycerol

After ethanol and carbon dioxide, the most abundant by-product of fermentation is glycerol, a compound frequently assumed to impact sweetness and viscosity in wine. Glycerol is a non-aromatic sugar alcohol (polyol) that typically appears in a range from 1-15 g/l in dry wines, with red wines frequently showing higher concentrations than whites. Most concentrations fall in the 4-9 g/l range. At concentrations above 5 g/l, glycerol does imbue wine with a slightly sweet taste, and while it may play a slight role in the taste of dry wines, its impact is likely unnoticeable in a wine with significant residual sugar. It does not affect perceived viscosity or weight at concentrations of less than 25 g/l, either. Botrytis infection leads to increased glycerol production, and sweet wines produced with infected grapes may contain 25 g/l of glycerol or more, but even at this level any increase in viscosity or sweetness through glycerol may be dwarfed by the more obvious increases due to residual sugar. Ultimately, glycerol’s effect on mouthfeel is likely too minor to isolate for all but a handful of botrytis dessert wines, yet it may add a featherweight sensation of sweetness to some dry wines. We do not recommend making an assessment of glycerol on the palate.

Balance and Complexity

“Balance” and “complexity” are the assumed hallmarks of quality wine. Balance refers to cohesion; “balanced” (or “harmonious”) suggests a seamless integration of structure, fruit, oak, and other components, wherein no single element overwhelms or stands out. The nature of balance is dependent on the type of wine: balanced styles of Barolo or Châteauneuf-du-Pape, for instance, look quite different than balanced Russian River Pinot Noir. “Balance” today is often code for moderation in alcohol levels, and—as it relies on a matrix of factors, to which each individual taster contributes a number of different thresholds and tolerances—it has always been a very subjective assessment. The meaning of the word—if not its actual definition—has shifted with time, and it is reflective of desired winemaking outcomes running in parallel with changing trends. Imagine the winemakers who chased phenological ripeness in the 1990s and early 2000s, only to dial back oak and alcohol in recent years. Surely in their minds the wines were always balanced. Sommeliers may value high acidity and herbal flavors in one wine, but an Australian show judge may mark the same wine down for excessive tartness and greenness. There are many instances when good tasters can agree to condemn a wine as imbalanced—a cloyingly sweet wine with too little acid, or a thin, light wine with too much evident new oak—but in general balance is a quality informed by our own individual expectations and desires.

Complexity, on the other hand, is essentially a sum of a wine’s aromas and flavors, and a measure of how much they change with time in the glass. For highly complex wines, one can simply say more about them. They evolve in the glass, and descriptors flow one after the other. For wines meant for the cellar, complexity of aroma increases with bottle age. On the other hand, wines of low complexity are akin to three-chord pop songs. They may be delicious and drinkable, but the tune is repetitive, and usually tires with repeated listens.

Finish

The wine’s finish is a final check of quality in tasting, and one that may be glossed over in our professional pursuits, which sometimes require rapid examinations of dozens of wines in a session. A wine’s finish—short, medium, or long—is determined by the length of time flavors and structure remain in concert on the palate after the wine is swallowed or spit. In other words, how long does its flavor last? In a good wine, balance on the finish should resemble the initial balance on the palate, and structure and flavor should retain similar proportions. Once flavor drops off, or a single element of structure overrides, the finish is over. For instance, some very inexpensive red wines, flavored with oak chips, can have a distressingly long oaky finish—but other flavors quickly recede. Some very acidic white wines, such as basic Muscadet, lose flavor almost immediately but an electric, lemony acid tang sails on. Both examples, despite the lingering presence of a component taste or flavor, would still be classified as short. When judging finish, some recommend simply counting it out—how long do the flavors really remain present, and in balance? If you find that they disappear after five or ten seconds, the finish is likely short, but if they continue for a half-minute or longer, then the finish is long. Ultimately, finish and complexity weave together to create quality in a wine.

Blind Tasting Conclusions

“Classic” Wines

When one is blind tasting in an attempt to discern the wine’s origin, the wine should be a classic representative of its type. To be termed “classic” from the perspective of blind tasting, a wine should fulfill four criteria:

1. The style of wine is produced from a variety (or varieties) commonplace in a particular region.
2. The wine has been grown and vinified through methods traditionally employed in the wine’s place of origin.
3. It is generally present and available in major international wine markets.
4. The wine exhibits one or more characteristics that make it distinctive.

Classic wines are not set in stone, and styles change as new generations and approaches arrive in winemaking regions. What is termed “classic” for a winegrowing region may no longer be the “classic” style 20 years later. Therefore, sommeliers must be continually aware, and continually tasting.

Make the Call

When tasting wines blind, sense memory and instinct can be invaluable, but they can be dangerous as well. A common blind tasting mistake sees the taster decide what the wine should be, rather than deducing what it is, then the taster creates an analysis of the wine that perfectly fits his or her preconception—but is totally wrong. Good instincts might result in a home run, but they also narrow vision, and often leave one blind to elements in the wine that do not support the initial call, as a sort of confirmation bias. On the other hand, deductive tasters collect data about the wine through the senses of sight, smell, and taste, and then analyze the information to arrive at the most likely result. The deductive method allows a taster to make a logical conclusion even if sense memory fails, and he or she does not initially recognize the wine. Wait to ponder the wine’s identity until the assessment of the wine’s qualities is complete; in this manner, one becomes a better blind taster and a more competent taster in general—instead of reciting what is expected in the wine (or what is expected to “score points”), the taster has to describe what is actually there.

Deduction is a funneling process. To begin, one is usually taught to determine the wine’s broadest origins: is it likely from the New World or the Old World, and in what type of climate was it likely grown? Historically, warmer climates have been generally associated with New World winemaking countries, and cooler climates have been associated with Old World climates. Therefore, Old World wines have been routinely characterized by higher acid and lower alcohol levels; conversely, New World wines have been characterized by lower acid and higher alcohol levels. In the modern wine world, this is no longer a reliable guarantee.

Concluding New World or Old World origin from alcohol and acid structure is overly simplistic and likely to lead you astray; Australian Riesling exhibits some of the highest levels of acid found in a white wine, and Barolo regularly exceeds 14.5% alcohol. However, I consistently find a perceptive character of fruit ripeness in New World wines that helps me separate the two. While a CDP may in fact have higher alcohol and lower acid than a typical Zinfandel, it is unlikely to achieve the vibrancy and fruit forward mid-palate of the later.
–Geoff Kruth MS

In fact, for many varieties today it may make more sense to think about the grape first, and the climate afterward. Varieties with clear impact aromas (e.g. Sauvignon Blanc, Gewürztraminer, Syrah) may reveal their probable identity readily, but determining climate may require more thought.

Major varieties are defined by certain classic parameters, and tasters must be familiar with these to make good, logical conclusions. Nebbiolo, for instance, is unlikely to be anything but high in tannin, and Riesling is typically high in acidity. Sauvignon Blanc typically shows pyrazine notes in cool to moderate climates. Cabernet Sauvignon is typically purple and densely colored in youth. And so on. But remember: no wine will ever resemble its classic profile exactly. Deducing variety involves a mental pro-and-con chart, as you build a logical case for why a wine may or may not be produced from a particular variety. If 90% of a wine’s characteristics resemble Cabernet Sauvignon, and 10% do not, resist the urge to make a left-field varietal call. Unless another variety makes even better sense, logic still favors Cabernet! On the other hand, there are those elements that utterly define a wine: if you have just decided that a red wine is low in tannin, it may smell like tar and roses but it is highly unlikely to be Nebbiolo.

Some wines carry the imprint of their variety clearly, but others are more difficult to interpret. When deducing variety, it is helpful to consider two or three similar varieties—or “laterals”—prior to making a final conclusion. For instance, Sangiovese and Nebbiolo might both be worth considering in the case of a sour, tannic red of garnet color, and Chenin Blanc and Riesling might both be possible in the case of a slightly off-dry, high-acid white. Remember that this is an opportunity to funnel toward a more logical conclusion, not just a time to blindly throw darts. If you find yourself regularly alternating between dissimilar grapes (e.g. Cabernet Sauvignon and Gamay), this is likely due to a lack of theoretical knowledge or a lack of trust in your own palate. Even similar varieties often have characteristics that distinguish them from each other; for example, consider the differences between dry European examples of Grüner Veltliner and Riesling, two grapes that tasters may confuse. Step away for a moment from precise fruit descriptors and poetic presumptions of loess and slate, and look at the big picture: Riesling is fruitier, more intensely aromatic, and floral (terpene-driven), whereas Grüner Veltliner has a vegetal, savory, and spicier (rotundone-driven) character, particularly at moderate levels of alcohol. Grüner may reach elevated levels of alcohol—and is then typically accompanied by whiffs of botrytis—but most classic styles of Riesling do not often clear the 14% hurdle. Riesling will invariably be high in acidity, whereas Grüner Veltliner will only be elevated, lacking Riesling’s sharpness. Grüner shows distinct bitterness. Riesling is more likely to be slightly off-dry, even if technically trocken. If you are stuck in the decision-making process, envision the wine from a guest’s perspective. Is your guest only interested in floral wines? If so, which of the two selections is a better fit? One could draw many of the same contrasts when evaluating Grüner Veltliner and Albariño—the latter is fruity and floral, and gains varietal character through terpenes. Making a logical varietal conclusion becomes easier the more and more you taste, but you can speed the process up considerably by understanding how to contrast varieties instead of solely relying on sense memory.

With a variety and climate in mind, one can begin to think about a country and region of origin. Theory is again vital; if you believe that a wine is likely a Cabernet Sauvignon-dominant blend, then consider the classic countries of production for the grape: France, the United States, Chile, Australia, and perhaps Italy. Yes, the wine could arrive from elsewhere but the taster should have a compelling reason why it would not likely be from one of the more dominant countries of production. Only a handful of grapes truly produce wines that adhere to the above definition of “classic” in more than one or two countries. Tempranillo, Nebbiolo, Sangiovese, Aglianico, Gamay, Torrontes, Grüner Veltliner, Albariño, Cabernet Franc…all of these varieties are considered “classic” only in their respective country of origin. For others, an understanding of modern winemaking practices and stylistic preferences in classic regions can helpful. For instance, one should understand oak. Chablis usually lacks the telltale signs of new oak aging, but new barrels are common in other classic Chardonnay regions. Grenache and Grenache blends in Priorat and Australia may see new barrels, but this would be extremely unlikely in Châteauneuf-du-Pape. New barrels may be employed for some Californian Sauvignon Blanc examples but would not be considered classic for Marlborough. Think about residual sugar: a Pinot Gris winemaker in Alsace likely has a higher tolerance for residual sugar than a winemaker in Northern Italy. Botrytis detected in a dry style of Riesling could sway a taster to Europe instead of Australia. Even the presence of Brettanomyces could provide a subtle clue: all other things being equal, a Californian Pinot Noir winemaker is likely to filter or otherwise deal with “brett” prior to bottling; a French vigneron may just chalk it up to terroir! The more you know about winemaker aims in classic winemaking regions, the more informed your blind tasting calls will become.

And then there is vintage. Nailing the year is a show-stopper for the uninitiated, but for a good taster it’s really an exercise to show off the work you have put into theory. First, determine an approximate age for the wine, based on your initial assessment on the nose and the follow-through on the palate. Is the wine youthful (less than 3 years old)? If so it should show no real signs of oxidation—unless intended by the winemaker—fruit should be primary and vibrant, and the wine may even retain some dissolved CO2. Which classic wines are most likely to improve with more than a few years in the bottle? Is there some degree of bottle age, evidenced through oxidation of color and aroma, and the development of complex tertiary aromas? Once you have a general age range in mind, consider the ripeness of fruit and the warmth of alcohol and try to decide whether or not the wine was produced in a cooler or warmer growing season. Think about Bordeaux: riper vintages in the 2000s include ’00, ’03, ’05, and ’09. 2003 was so hot that the wine should really show overripe character. 2005 and 2009 were bigger vintages than 2000, and the difference in oxidation over a nine-year span should be fairly pronounced, particularly as 2009 is still a very young vintage. Suddenly options have narrowed considerably. And if there are two very similar vintages, like 2006 and 2008 in Bordeaux, you might conclude that it is either one or the other, and leave it at that.

Selected Bibliography

Bakker, Jokie, and Ronald J. Clarke. Wine Flavour Chemistry. Oxford, UK: Blackwell
     Publishing, 2004.

Jackson, Ronald S. Wine Science: Principles and Applications. 3rd ed. Burlington, MA:
     Academic Press, 2008.

Moreno-Arribas, M. Victoria, and M. Carmen Polo, eds. Wine Chemistry and
       Biochemistry. New York, NY: Springer Science+Business Media, 2009.

Ribéreau-Gayon, P., et al. The Handbook of Enology: Volumes I & II. 2nd ed. Chichester,
      UK: John Wiley & Sons, 2006.