Topic of the Week 10/23/17 - Introductory and Certified

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This week: Tannin

Describe some of the ways a winemaker can mitigate or increase the tannins in red wine.

  • Hi!

    Tannins , which are from the skins, seeds and stems of a grape, are far more pronounced depending upon length of skin contact, crushing methods and use of oak. Tannins are also called polyphenols and are a natural occurrence in plants. A winemaker may use smaller, new oak  when aging their wine and this will impart wood tannin. Larger, older or neutral  barrels will impart less wood tannin. Longer skin contact will increase levels of tannin and if the crushing process is not done gently it may release unwanted tannin. The less maceration the wine undergos  the less tannic their wine will live to become. 

  • I believe any filtering or fining of the wine can also soften the tannin profile

  • This is a huge subject; A wealth of various websites and books on the matter were researched to produce this response, and I could have spent several more days and made it three time as long. 

    The subject of Tannins in wine is vast - entire books have been written on the subject. In wine, the tannins are included in virtually every part of the plant (even in very low concentrations in the juice itself). Leaves, Stems, Wood and Seeds all have Tannins. Soft, silky, velvety, youthful, puckery, aggressive, harsh, bitter, astringent: These are all adjectives used in winespeak to describe the many taste sensations from tannins in red wines. 

    Not all tannins are created equally. The two main sources of tannins in red wine are grape plants themselves (including seeds, skins and stems), and oak barrels, but if we dissect a grape berry and stems, we will find very different types and polymerization of tannins. Some are desirable and some aren’t. To further determine how control of Tannins in wine is executed, let’s examine the three classes of tannins: hydrolyzable, condensed, and complex.

    The class of hydrolyzable tannins, so called because the compounds are attached to sugar molecules and which can be cleaved, or hydrolyzed, into their subcomponents, gallotannins and ellagitannins. These are relatively soft tannins found in low concentrations in grape juice; the ellagitannins castalagin and vescalagin are found abundantly in the woody Quercus (oak) and Castanea (chestnut) plant species. That’s why chestnut barrels were once popular only to succumb to the now more popular oak barrels or oak adjuncts, such as staves, cubes and chips, which impart additional and more favorable aromas and flavors. And if you want to add a more pronounced yet rounder mouthfeel, add a tannin mix specifically formulated with gallotannins and ellagitannins. 

    The class of condensed tannins, so called because of their ability to polymerize or bind with anthocyanins, and also referred to as proanthocyanins, are found in seeds and to a lesser extent in stems, and relatively little in the skin of red grapes. In general, you can expect that the thicker and the more colored the grape skin, the higher the concentrations of tannins and anthocyanins.
    Condensed tannins are all derivatives of a flavanol (a class of compounds found in plants and certain fruits and vegetables) known as catechin. Catechins found in seeds and stems are very bitter and astringent, particularly because of their much smaller degree of polymerization, compared to the beneficial ones found in the skins; that’s why grapes are usually destemmed prior to crushing and why crushing of or extended contact with seeds should be avoided.

    To become Complex Tannins, the tannins continue to evolve over the course of the life of a wine, both in bulk in carboys or barrels and in bottles. During aging, both hydrolyzable and condensed tannins polymerize into large, high-molecular weight complex tannins that also bind to anthocyanins and precipitate as tannin-anthocyanin complexes, resulting in a lighter color and reduced bitterness over time. This reaction and sedimentation occurs over a long period of time depending on wine chemistry and storage conditions.
    Tannin-anthocyanin complexes are too large to pass through a filter medium and can therefore be filtered out to achieve the same level of clarity as extended aging without filtration. But filtration naysayers argue that other critical compounds are also filtered out — which ones, we don’t know — and that is the essence of the debate regarding the quality of filtered vs. unfiltered wine.
    Since there is no maceration of juice with grape solids in white winemaking, tannin content in unoaked whites is negligible; however, red winemaking is all about maceration. There are some interesting chemical properties of and interactions between catechins and anthocyanins at play during maceration and fermentation that need to be managed to produce a desired style of wine.
    There are several specific winemaking techniques to control the amount of catechins and anthocyanins extracted into wine. The extent of extraction depends on phenolic ripeness of the grapes — that is, the amount of phenolics in grapes, which depends on viticultural practices, soil condition, and climatic conditions of the growing region and season — and winemaking practices such as cold soak maceration, fermentation environment, duration of skin contact during maceration and fermentation, cap management and extended post-ferment maceration.

    If you want to reduce the Hydrolyzable  and Concentrated Tannins in Wine: 

    First, because it is worth repeating, destem grape bunches. You want to remove as much of the stems as possible, particularly very green (as opposed to brownish) stems. Catechins in stems are very harsh and will require years to mellow out before the wine is approachable.
    Second, anthocyanins are more soluble in grape juice than in alcohol (i.e. wine), whereas catechins are more soluble in alcohol than in water. To extract more anthocyanins for a deeper color, perform a cold soak maceration before fermentation.
    Cold soak maceration involves soaking grape solids in the juice for several days to a week at a cold temperature, down to 45 °F (7 °C) or preferably lower to ensure fermentation does not start on its own. Sulfite lightly at crush, up to 25 mg/L, to minimize bleaching effects of sulfite, which would go counter to your objective of extracting more color, and to minimize catechin extraction. And be sure to perform daily punchdowns to stimulate anthocyanin extraction and to reduce any risk of bacterial infections.
    During cold soak maceration, there will be some extraction of skin catechins, but these are also precursors to browning reactions in the presence of oxygen (air), and so, their extraction should be limited until fermentation is started — fermentation provides protection against browning by deactivating the culprit enzymes. This is usually not a problem but, again, do not over-sulfite as that would otherwise hasten catechin extraction and increase the risk of browning during maceration.    
    Third, opt for a relatively hot and quick fermentation to favor extraction of catechins from the skins and to minimize contact time with seeds. Anthocyanin extraction will continue, albeit, at a much slower pace. A typical fermentation should last five to seven days until dryness (when the SG/Brix read 0.995/-1.5). If you want to minimize catechin extraction because you intend to drink the wine early, rack the wine earlier, say at an SG/Brix of 1.030/7.5, and then press. And fermentation temperature should never exceed the mid-80s °F (below 30 °C), which could otherwise result in a stuck fermentation.
    Fourth, only perform a (cold) post-ferment maceration if you intend to create a rich, bold, full-bodied style of red meant for aging. During this phase of winemaking, extended contact with seeds will hasten extraction of harsher catechins. 
    Alternatively, perform delestage during fermentation to remove as much seeds as possible if you want to do a post-ferment maceration to extract more skin catechins. Delestage is a two-step “rack-and-return” process whereby fermenting red wine juice is separated from the grape solids by racking and then returned to the fermenting vat to re-soak the solids, and then repeated daily. 

    In addition to adding complexity and mouthfeel, there are other benefits to having Tannins in wine:

    One benefit of tannins is that they act as natural fining agents by binding to and precipitating haze-causing proteins. Protein stability in tannic red wines is therefore not of concern; however, wines processed very quickly (for early drinking) with little or no tannin extraction (such as whites) should still be tested for protein stability before bottling. 

    The most important benefit of tannins is that they are natural antioxidants — a red wine’s aging potential is largely based on its tannin content. Tannins have an affinity for binding to oxygen to protect wine from the effects of oxidation. By restricting the availability of dissolved oxygen to oxidation-prone compounds, less oxygen is available, for example, to transform phenolics into browning compounds and alcohol into acetaldehyde, a common spoilage compound.

    When aiming to control or remove Tannins, there are a number of possible solutions if you have extracted excessive tannins, all very effective. The extent of tannin “removal” depends largely on timing, i.e. trying to remove small vs. large molecules, and concentration. 

     Blending of varietals is perhaps the oldest key method to mitigating tannins. Varietals differ in tannin content in both ratio and overall total tannins.  
    Tannins have a strong affinity for proteins, and so, you can fine using a protein-containing fining agent such as egg whites, gelatin, or isinglass. Since gelatin comes in different formulations, i.e. low vs. high molecular weight, choose the one that best fits your needs based on the manufacturer’s recommendations, and avoid overfining. Gelatin formulations with different molecular weights show preferential affinity for tannin size. 
    PVPP, short for polyvinylpolypyrrolidone, is a highly insoluble, high-molecular weight synthetic polymer that is effective in absorbing and precipitating small tannins. And so, PVPP is recommended for early-drinking wine or where bitterness needs to be toned down.
    Another potential solution is gum arabic (gum acacia), a natural gum extracted from the sap of specific species of African Acacia trees. It is very effective in reducing tannin astringency and increasing the perception of body or volume, and reducing the perceptions of acidity and tannin harshness, while adding body.

    And lastly, you can tame tannins by readjusting the wine balance by tweaking sugar and acidity contents. To quote Émile Peynaud’s guidelines; keep them in mind when tweaking your wine. “A wine tolerates acidity better when its alcoholic degree is higher; acid, bitter and astringent tastes reinforce each other; the hardest wines are those which are at the same time acid and also rich in tannins; a considerable amount of tannin is more acceptable if acidity is low and alcohol is high. The less tannic a red wine is, the more acidity it can support (necessary for its freshness); the richer a red wine is in tannins (necessary for its development and for its longevity) the lower should be its acidity; a high tannin content allied to a pronounced acidity produces the hardest and most astringent wines.”