A Year in The Vineyard

The Harvest

2015-04-07T21:20:00Z

Harvest truly is a magical time. It’s the culmination of a year in the vineyard. The world recedes to the end of a long tunnel, as all daily obligations are temporarily relieved, allowing pure, crystalline focus on the task at hand. This is true in all forms of agriculture, but particularly so in wine. For us, harvest is both the completion of our farming year and the beginning of our winemaking cycle, and it provides relief from the distractions of the wine business—the constant, daily interruptions that enrich our lives but can be overwhelming without a break. During harvest there are no sales calls, no tastings, fewer emails, no business meetings—only the daily struggle to make the right decisions and to somehow logistically pull those decisions off. What incredible pressure and excitement this creates! Everything hinges on this one thing: the harvest.

The most fundamental decision of harvest, the thing that sets everything in motion, is timing: when do I pick the grapes? This is the winemaker’s prerogative. In California and in other industrialized winemaking regions around the world, the winemaker and the grape-grower are usually two different people, and in almost all cases the winemaker is the one who decides when to pick the fruit. The grower (who could be a farmer, a vineyard manager, or a viticulturalist) has tended the grapes all year, either with input from the winemaker or on his/her own, but the winemaker assumes responsibility for this pivotal decision—because the timing of harvest is fundamental to determining wine style. The grower then organizes the people and the equipment to make the harvest happen and delivers the fruit.

Choosing when to pick is a personal decision, and one that causes a huge amount of stress and anxiety on the part of the winemaker. Winemakers can get downright strange during this time; it’s definitely one of those times when a person’s true colors come out. The whole vintage is riding on not screwing it up! Sometimes compromises have to be made due to shortages in labor availability on the part of the grower, or tank space on the part of the winery. (Of all the reasons to botch a vintage, these are among the stupidest and most frustrating for all involved, but sometimes it just can’t be helped.) Other times weather forces your hand—but you can’t blame the weather for poor planning, and watching the forecast with an eagle eye is part of the job too. In addition to following the National Weather Service, we subscribe to two different paid forecast services. If the grapes are close, and a rain or heat event is coming, it might be wiser to pick now instead of letting the fruit ride through that weather. Sustained warm weather, especially at night, means that ripening will happen quickly, so we anticipate big changes from day to day. Conversely, cooler weather might stall things out. Morning dew can lower sugar levels, while low humidity can cause sugar to skyrocket. Weather plays a huge role.

While unanticipated logistical challenges and changing weather can really induce stress during harvest, the fruit itself tends to go through fairly consistent stages as it ripens. The three main milestones of the growing season are bloom, seed-hardening (lag phase), and veraison. Tannins develop early, between bloom and veraison. While lots of things influence tannin development, the biggest factors are probably water stress, vine vigor, and (to a certain degree) sunlight. At veraison, the vine starts to produce anthocyanins in the fruit as a response to the movement of sugar into the berry. Pyrazines, which are created in the fruit before veraison, start to degrade as the fruit ripens, and other flavors start to be developed. It is important to note that the only things really moving through the vine into the fruit are sugar, potassium and some other minerals, and hormones—all of the color, tannin, and flavors are manufactured inside the grape berry itself.

As we move into the harvest window, all the anthocyanins and tannins are already present, but a bunch of key things are still happening: sugar is still moving into the berries, increasing potential alcohol; potassium is still moving into the berries, reducing total acidity; malic acid content is dropping as the berries use it as a source of energy; tannins and anthocyanins are combining into larger molecules called polymeric pigments, softening the astringency of the future wine and stabilizing the color; pyrazines are degrading, causing the fruit to taste less herbal or vegetal; fruity compounds are being created, and the types of fruit compounds are changing—the red fruits are giving way to black fruits, and eventually to cooked fruit and jam. Each of these ripening parameters is a moving target, and it is by detecting and predicting them that the winemaker dictates wine style through that all-important decision, the timing of harvest.

The most basic parameter to help determine the harvest date is Brix, a measure of dissolved soluble solids in the juice. Brix measurement does a pretty good job of predicting the final alcohol level of the finished wine. Our whole industry tends to measure degrees of Brix throughout the ripening process, so it provides a lot of indirect information about the grapes. We can gauge speed of ripening, both predicting where it is going and getting a sense of the current condition and balance of the vines. And it gives an estimate of general wine character; for example, Cabernet Franc harvested at 22° Brix will probably make very different wine than Cabernet Franc at 26° Brix—most likely, one wine will be light and green, and the other wine rich and black. Brix can be tricky, because it measures all soluble solids, not just sugars, so it is not completely accurate, but it provides a great general guide. And, once you buy a refractometer, it’s a free test. In the winery we usually test for glucose/fructose to get a more accurate gauge of potential alcohol, but that test is expensive. Brix provides a fine method to regularly monitor ripening, it just won’t pinpoint the final alcohol content with 100% accuracy.

The general rule of thumb is that you multiply Brix by somewhere between 0.56 and 0.61 to anticipate the final alcohol of the wine. So 24.5° Brix (x0.58) would result in 14.2% alcohol by volume. But it is just an estimate: factors like different sites, varieties, yeast strains, tank types, and fermentation regimes all impact the exact alcohol conversion.

Most winemakers monitor the change in pH and TA. In general, as the fruit ripens, pH goes up and TA goes down. This is due to a combination of malic acid respiration by the berries and tartaric acid buffering by potassium. (Potassium has an affinity for tartaric acid, making potassium bitratrate, an insoluble salt—the exact same crystals, or “titrates,” you see in a bottle of wine.) pH and TA will shift some more during fermentation, especially in reds, as more potassium leaches out of the skins; nonetheless, testing the fresh-squeezed fruit juice will give a very good idea of what is happening with ripening and what ballpark one can expect with wine acidity.

Malic acid itself is a nice data point to look at to see how much fuel is left in the grapes. High malic suggests that ripening is not complete, while very low malic might cause one to wonder if the berries are as ripe as they are going to get, regardless of whether the Brix has come up enough or not. A high malic acid figure might be something over 3 or 4 g/l, while a low number might be 1 g/l or below.

Some winemakers actually test the fruit for the phenolics. They send clusters to a lab that grinds up the whole berries or the skins and lets you know how much of the tannin content has polymerized with the anthocyanins to form polymeric pigments. This type of analysis tends to be done by the “long hang-time” school of winemakers, who are looking for concentrated, supple wines, and they are willing to sacrifice fresher red-fruit aromas in the search for plusher texture.

There are reams of data available, but at the end of the day our senses are still the most important tool for determining harvest timing. Most winemakers visually inspect the vineyard regularly as harvest is approaching, and they taste the fruit as much as possible. The condition of the leaves says a lot. Are they bright green and crisp, or starting to yellow and soft? Are the leaves starting to fall off? When you taste the fruit, is it softening or still hard and crunchy? Does it feel smooth or rough? Is some color bleeding out of the connection to the stem? Do the little filaments that extend from the stem into the berry pull out cleanly, or are they stained purple? Do the seeds separate cleanly from the pulp? Are they browning? Does the skin stain one’s fingers purple? Are birds starting to eat the berries? Are the skins chalky or silky? Is there a bell pepper aftertaste? Are some berries starting to fall off? Can you smell fruity aromas walking down the rows?

When the decision to harvest has been made it falls on the grower to get the fruit picked. At Matthiasson Wines the grower and the winemaker are the same person—me—but usually the winemaker has to communicate far enough in advance with the grower to get the pick scheduled. One person can pick one to two tons per day, depending on the size of the clusters and the health of the vineyard. Most harvest crews have eight people picking four-row swaths, one tractor driver, and two people picking out leaves and bad fruit from the bins. In California it is customary for the workers to be paid by how much fruit they pick, not by the hour. This lets them earn more per hour than they normally would as long as they work really fast. Ideally they get a full day’s wages in a few hours, and the fruit is picked and delivered in the morning, when it is cool, giving the winery the rest of the day for processing. When harvest is in full swing there are days when the workers have to start at night and put in long hours, which is physically brutal, but they are able to save money for the winter slowdown. Access to labor is always a challenge.

Mechanical harvesting is the norm in the interior valleys where the price of fruit is too low to justify harvesting by hand—there just isn’t enough labor in the state to hand-harvest everything. Mechanical harvesting requires huge, expensive tractors to straddle the vine rows, beating the vines to literally shake off the fruit. If the machines are set up well it can be a perfectly fine practice for quality red fruit—red fruit can generally handle some oxygen exposure—but white fruit can get excessively oxidized and tannic from the juice-skin contact (unless some oxygen exposure and skin contact is part of the desired wine style). Things are changing fast with mechanical harvesting, and there are some new high-tech harvesters with on-board sorting capabilities. There have also been great strides in developing harvesters that are much more clean (fewer leaves, stems, and sticks) and gentle (more whole, unruptured berries).

Some growers in the high-end coastal areas have started harvesting mechanically to save money and avoid the harvest labor crunch, but most premium California regions continue to rely on harvesting by hand. In many North Coast areas, it is just not possible to use a machine—many vineyards are too small, or they don’t have large enough turnaround areas for the big equipment, or they have cross arms or other trellis configuration issues that prevent mechanical harvesting.

A big trend that has developed over the past decade or so is night-harvesting. Mechanical harvesting has always taken place primarily at night to minimize oxidation by picking the fruit as cold as possible. Hand-harvesting, though, has traditionally commenced at first light in the morning. Makes sense—the fruit is picked as early as you are able, yet you can see what you’re doing. Lately, however, it has become more common for hand-harvesting to happen at night as well. The growers pull huge lights behind an extra tractor and the entire harvest happens between midnight and 8:00 am. This captures the fruit at its coldest point and gives the winery the entire day for processing. More and more wineries are sorting at the winery these days, so the time it takes to crush the fruit and fill a tank has slowed way down, leading winemakers to request fruit delivery earlier and earlier in the day.

The best day of harvest is always the first day—it is so exciting and pleasurable to get started picking the fruit; the second-best day is always the last, when we are finally finished. Plenty of beer is consumed on the first day, and plenty more tequila on that last day! All year we look forward to harvest starting; after it starts we look forward even more to it ending. The rhythms of the year are one of the pleasures of viticulture, and harvest is the crescendo of the annual cycle.

Disease Management: The Big Three

2014-04-21T14:17:00Z

Like death and taxes, battling diseases of grapevines can’t be avoided. Managing grapevine diseases is an integral part of tending vineyards; the challenge is due to one simple, modern predicament: many of the diseases are from the New World, and Vitis vinifera is from the Old World, so it didn’t evolve any natural resistance to them. European grapevines and grapevines of European origin have to contend with North American diseases that they don’t have the genetic ability to fight. This problem is not getting any better—most of the varieties that we grow today are propagated by cuttings that date back to an era before grapevines or their diseases traveled across the Atlantic; in some cases, the varieties even predate Columbus. Meanwhile, on this side of the pond native vines have had plenty of time to evolve ways to coexist with our diseases. The Vikings (my Icelandic ancestors) saw it firsthand: Vinland, as they christened North America over 1000 years ago, was full of these eponymous, native vines, hosting the worst of vineyard diseases that we currently battle.

If pruning shears are the primary tool of the viticulturist, the sprayer is a close second. Whether the farmer is organic, biodynamic, or conventional nuke ‘em, until newer disease-resistant grapevines are accepted by the wine world, there is no way to grow the varieties we are accustomed to, like Riesling or Pinot noir, in 99.99% of the world without spraying something. Andy Walker at UC Davis is currently developing non-GMO classically bred mildew-resistant vines, and I am very excited about those possibilities—but they will be entirely new varieties, and as you know, the wine world is quite traditional. Müller Thurgau and Zweigelt are finally gaining some acceptance, so who knows? Maybe they will take off. Maybe not.

Powdery Mildew

Getting away from pie-in-the-sky and back to the trench warfare of disease control, the main organism that viticulturalists fight worldwide is powdery mildew (Uncinula necator). It is closely related to the powdery mildew species you see on roses, melons, squash, and crepe myrtle. It has an over-wintering phase and a summer phase, and as a foliar fungal pathogen it has a very unusual ability during its summer phase—it doesn’t need free moisture to germinate. Its spores can hatch and infect dry leaves or berries. Most fungal pathogens need free moisture to do their nefarious business. Powdery mildew doesn’t actually like to get wet, which is one of it’s weaknesses that we can exploit—part of the killing effect of the sprays is literally the “washing” effect of the water: the fungal hyphae (“hyphae” are thread-like structures that make up the body of the fungal organism) burst due to permeable membranes that create osmotic differential between the solute-filled moisture within their cells and the pure water outside. (Quick chemistry refresher: water is always drawn across a membrane from the side with less solutes—salt, sugar, and amino acids are all solutes—to the side with more solutes, until the two sides are balanced. This is called by osmosis. That is why soaking in epsom salts draws fluid out of our skin, while soaking in pure water puffs our skin up. It’s an important concept for all kinds of processes with plants, fungi, and other organisms, including humans.)

Powdery mildew over-winters as tiny, hard, BB pellet-shaped brown or black specks of dust, just barely visible to the naked eye, called cleistothecia. These little fungal escape pods have evolved to survive a hard winter on the bark and then hatch spores during budbreak. With a moderately warm rain event, they release their ascospores, perfectly timed to infect the new little grapevine shoots that are just appearing from under the bud scales. After this initial infection the organism no longer needs any rain events or free moisture, reproducing asexually during its summer phase as fast as every five days. Its spores, called conidia—which are like little pearls on vast forests of teensy-tiny little white stalks—give the leaf a powdery appearance, and hence its name. Powdery mildew was accidentally introduced into Europe from North America in the mid-1800s, in the same general timeframe as phylloxera and downy mildew. It’s less deadly than these other two pests, but makes up for it with its ubiquity.

Powdery mildew has exquisitely co-evolved with grapevines. As such it doesn’t kill the vines, but it does significantly weaken them. On the leaves and canes it reduces photosynthesis, cold-hardiness, and carbohydrate storage; it slows ripening, and retards leaf growth. On the berries it causes cracking (leaving them susceptible to bunch rots), slows or stops ripening, and gives the wine a distinct mushroom-like aroma. You can sometimes detect an outbreak in a vineyard by noticing the mushroom odor as you walk down the rows.

Luckily there are good organic materials to prevent powdery mildew. It reproduces so fast, however, that if you let your guard down for more than a couple of weeks, it will roar to life in what seemed like a completely clean vineyard. For this reason, it can’t currently be managed using the Integrated Pest Management (IPM) principles of monitoring and early detection; instead, the vineyard needs to be sprayed at regular intervals preventatively (there is new technology in the pipeline to detect powdery mildew, which should drastically cut down on spraying, but it’s not ready for widespread adoption yet). This means that grape growers—pretty much anywhere in the world—have to get used to climbing on the tractor wearing a respirator and a raincoat and driving up and down the rows every week or two during the months from budbreak to véraison. If the temps are between 70-85° for much of the day the intervals need to be tightened, and if hotter or cooler than that range it is okay to space the sprays out a bit.

The main tool to fight powdery mildew for the past 150 years has been sulfur. As a spray or a dust, sulfur kills the spores as they germinate, preventing infection. It doesn’t do much once the fungus has gotten a foothold, so it must be used preventatively. Sulfur is used both by organic and conventional growers. You have to be careful with sulfur, though: if used too late in the season it can persist on the grape skins, providing a substrate for the yeast during fermentation to make sulfur off-aromas (rotten eggs/H2S, etc). Late-season sulfur applications in areas with very high powdery mildew pressure can be one of the causes for “flintiness” or other reduced mineral-type aromas in the wine. Sulfur can also burn the leaves and the fruit if applied before a hot spell.

Oil can be sprayed on the vines to smother powdery mildew, and is a good organic option. It works well, especially early in the season when the shoots haven’t grown much, and are easy to thoroughly cover with the spray solution. Oils are hard on the vines, though, especially if the weather is very hot or very cold. They smother the vines too, reducing photosynthesis; and they will burn the vines if applied too close to a sulfur application—those two materials don’t mix. Oil, sulfur, and copper (copper is for downy mildew, not powdery mildew) work on the principle that they are less toxic to vines than they are to the disease. In other words, they kill leaves just as easily as they kill the disease if they are applied at a high-enough rate. So it never feels good to spray them—it’s always a teeth-gritting operation.

There are some newer organic materials based on fermentations that work okay—not great—but free from the problems associated with the toxicity of sulfur or oils (Serenade, Sonata, and Actinovate are the most commonly available products—they are made by fermenting organisms like bacillus subtilis). Some growers are experimenting with milk and whey, which create a competitive environment for the disease organism and produce free radicals that kill the diseases. Nutrients like calcium, potassium, and silica help the plants ward off the disease on their own (not a stand-alone strategy, but an adjunct), and they can be sprayed on the leaves preventatively—the leaves can use the nutrients to strengthen themselves. The biodynamic spray horsetail is a good source of silica for this purpose.

If you leave organic farming behind, powdery mildew is fairly easy to control with the suite of new synthetic fungicides that are now available. Many of them are systemic, and they all have a much longer-lasting residual effect on the plants. New research about the unintended consequences of these materials is coming out all the time. Some of them are potent endocrine disrupters. They may be causing problems with bees. There are serious concerns with these materials, and so with our farming we choose to restrict ourselves to the organic materials that break down harmlessly in the environment.

Powdery Mildew

Downy Mildew

The next most important disease worldwide is downy mildew. Regardless of its similar name, downy mildew is a completely different organism than powdery mildew. Downy mildew originated in the Eastern United States, just like powdery mildew and phylloxera (which is an insect, not a disease, so we’re not covering it here). It’s technically in the class of fungi called water molds, and it requires warmth and free moisture to germinate. As such it’s not always a big problem in the dry Mediterranean climates, and is almost unheard of in California, but it’s a major problem anywhere that gets much warm summer rainfall—regions throughout France, Northern Italy, the Eastern United States, Western Australia, Germany, etc. Unlike powdery mildew, downy mildew will completely defoliate the vine if left unchecked. It is a devastating disease, killing any and all living tissue is a short period of time.

Downy mildew has an interesting spore that causes infection, called a zoospore—it actually swims with little flagella, like a sperm. Powdery mildew spores, on the other hand, just blow around in the wind. The swimming action of the downy mildew spore necessitates moisture to germinate and infect.

Downy mildew is controlled organically with various preventative copper sprays (Bordeaux mix, copper hydroxide, copper oxide, etc.), but copper builds up in the soil—if sprayed over enough years it can accumulate to toxic levels. This is in contrast to sulfur, which is absorbed by nature in other benign ways: sulfur is eaten by soil organisms, taken up by plants as a fertilizer, and incorporated into soil humus. Because of the soil buildup, copper sprays must be minimized, and growers struggle to control downy mildew organically. There is a lot of work going on in Europe to find cocktails of plant extracts, compost teas, and biodynamic preparations that will control downy mildew with the toxic impact of copper.

There is an environmentally benign—but not certified-organic—control for downy mildew: phosphorous acid. Use of this tool represents one of the many challenges raised in meshing totally organic farming with sustainable farming. Phosphorous acid is a synthetic product, and therefore not organically approved, but it is harmless in the environment: it breaks down into phosphorus fertilizer. In most cases organic farming and sustainability overlap, but not always. There are gray areas. As time goes on we will hopefully able to fine-tune our organic methods to mesh completely.

Downy Mildew

Eutypa and Botryosphaeria

The third most important disease challenge is the devastating trunk-rotting duo of Eutypa and Botryosphaeria. They are two different organisms with virtually identical behavior. Also called Dead Arm and Eutypa Dieback, these two suspects are the number-one reason we don’t see more old vineyards. The spores shoot into the air during rain events, and infect vines through fresh pruning wounds, slowly working their way into the vines, choking off the flow of sap, destroying the productivity, and eventually killing the vine. You start to see the disease when the vineyard is around ten years old, and it can be devastating by the time the vineyard is twenty years old. In many cases, by the time the vineyard is twenty years old the diseased wood is so bad that the vineyard needs to be replanted. Without dead arm, the same vineyards could last for one-hundred or more years.

Some varieties, like Zinfandel, are less susceptible. So you see more old-vine Zinfandel vineyards. Also, with head pruning you make fewer big cuts in the vine, which helps to reduce the number of new infections—the bigger cuts, into thick old wood, are much easier pathways for the disease.

Over the past decade or two we have learned how to minimize the disease, but it’s an added cost, and presents some challenges. In California, pruning in early spring rather than midwinter makes a big difference because the spores typically exhaust themselves earlier in the winter rainy season. More spores are flying around in the first fall/winter rains; less are out in the spring rains. This is a tough to do, though: it significantly reduces the winter pruning window, leaving you only a few weeks to prune prior to budbreak rather than the entire winter. A labor nightmare as you might imagine, but it’s become the norm for a lot of growers.

Painting the pruning wounds with fungicide is another option. These materials have historically been pretty toxic, and don’t last long on the pruning cuts, leaving organic farmers to make their own homemade wound treatments, with ingredients like compost, manure, clay, or whey. These concoctions work by encouraging competitive fungi. There is finally an effective and non-toxic wound treatment available called Vitiseal, based on cinnamon oil. We’re hopeful that this new Vitiseal is going to make a big difference in vine longevity.

In many vineyards, once Eutypa starts showing up enough (you can see the dead spurs and cordons), you cut back the vines and retrain them. If this is done diligently you can maintain the vineyard in pretty good shape, but it’s a lot of work, and the vines are out of production until they are retrained.

Eutypa

These are the big three diseases. There are many more diseases that we fight, like Botrytis, Esca, and Armillaria, but none of them are as ubiquitous and potentially devastating as powdery mildew, downy mildew, and Eutypa/Botryosphaeria. As a grape-grower you need to think about mildew every day in the summer, and Eutypa/Botryosphaeria every day in the winter. Fighting them is a constant battle, and it’s one of the core aspects of growing grapes, right up there with pruning and soil fertility. It’s another reason, though, that the art of viticulture is so interesting.

Yield and Wine Quality

2013-03-20T09:55:00Z

What’s the deal with yields? Or terms like “crop load,” or “vine balance?” What does it mean to ”green harvest” or to “restrict yields?” Why would one do that? Is 30 hectoliters per hectare always better than 60 hectoliters per hectare, or two tons per acre better than four tons per acre? How is wine character actually changed by adjusting to different crop levels? These terms get thrown around, but what do they really mean?

The Green Harvest

Fruit thinning (“green harvesting”) is a key technique used to lower yields, and it is one of the most mysterious viticultural practices; besides science, it involves habit, compulsion, penance, fear…a whole host of impulses that have very little to do with normal farming but everything to do with wine, that most irrational of human agricultural products. Fruit thinning is extremely emotional for farmers and winemakers, and science often has very little to do with this incredibly costly and often wasteful practice.

As a farmer and a vineyard consultant who devotes a huge amount of mindshare in the summer to helping my clients figure out how much fruit to keep on the vines, I’ve struggled to understand the process of fruit ripening, and how it is affected by different amounts of fruit. This is not a trivial matter—besides the impact on wine style from fruit thinning (note that I said “style,” not “quality”…much more on that later), economics are a huge factor. I’ve calculated that for one of my clients (a vineyard owner who makes a $350 bottle of wine) each scraggly little bunch of grapes that we cut to the ground represents twenty dollars worth of wine! And this doesn’t include the labor to do the fruit thinning, which is very slow and exacting. But the client points out that fruit is only worth what you can sell it for, and if that thinned fruit cannot go into the bottle of wine it is worthless; it is, in fact, a negative. So the judgment of whether or not that fruit needs to be thinned off is obviously an incredibly important decision.

For the most part, fruit thinning as a standard quality vineyard practice is a fairly recent phenomenon, having developed over the past thirty years or so. There are plenty of exceptions, but this generality is important because it is a piece of the global wine style shift over the past few decades. The practice of fruit thinning originally evolved in high-end estates in cooler growing regions and slowly diffused out to the rest of the grape-growing world. Adoption of the practice was not overnight--cutting fruit to the ground was (and still is) something that is extremely difficult for the average practical-minded farmer to accept. A good farmer will take fruit off of young, weak, or sick vines, but this is a critical viticultural practice to relieve vines that cannot handle their fruit load, not a "green harvest"—it's more of a fine tuning than a yield restriction.

The basic principle with fruit thinning is that with less fruit on the vine, the rate of sugar accumulation is increased in the fruit that remains. Since sugar is accumulating steadily over time, the earlier in the season it is done, the more sugar ends up in the remaining fruit; or, the more fruit that is thinned at a given time, the more sugar ends up in the remaining fruit. Basically we’re talking about timing and severity: these are two of the levers that can be pulled to increase sugar in the harvested fruit. The third lever is the amount of leaf area that the vine has working for it. Leaves make sugar through photosynthesis, and the vine transports that sugar to the fruit, where the sugar slowly increases in concentration during the ripening period. Less fruit with the same amount of leaves, more leaves with the same amount of fruit, or more time with the same amount of leaves and less fruit: all of these scenarios lead to more sugar in the remaining clusters. The main thing is the ratio of leaf area to fruit load over time.

There are other factors that influence sugar accumulation, such as the nutrient or water status of the vine, the percentage of leaves receiving sunlight, the average age of the leaves, the virus load in the vine, and so on; but if all of these things are equal, the ratio of leaves to fruit will greatly determine the rate and amount of sugar loading in the grape berries.

The biggest impact that higher sugar levels have on wine style is obviously a higher level of alcohol in the wine. There is a direct and linear relationship between sugar and alcohol. Fruit thinning and sugar accumulation is not linear, though. The leaves sense the crop level and compensate in their photosynthesis to a certain degree. A higher crop load results in more efficient leaves, and a lower crop load results in less efficient leaves. Therefore, simply cutting the crop load in half will not double the sugar production. Thinning fruit does impact sugar production, but a lot of fruit needs to be thinned from a vine before it experiences even modest differences in sugar accumulation. Cutting the fruit in half or more might result in as much as a 10-20% increase in sugar—that is around the maximum that sugar can be increased by manipulating crop load. That small difference makes a big difference in wine style though. It could increase a potential alcohol of 11% to 13%, which could be a critical difference in a cool climate like Switzerland. It might also raise a 13% wine to 15% in a warmer region.

Greater sugar accumulation as a result of fruit thinning seems to have an impact beyond simply raising alcohol levels. This is not a well-studied area, and there is a lot of anecdotal information out there—much of which is misleading. One thing we do know is that sugar movement into the fruit around veraison seems to trigger a signal for the fruit to start manufacturing anthocyanins. Earlier anthocyanin production can result in more color in the fruit at harvest. Anthocyanins complex with tannins in the wine, softening the mouthfeel and enhancing mid-palate concentration. Other ripening parameters are almost certainly enhanced; anthocyanins are just easier to measure, so that is why they are so often studied. For a modern, dark, concentrated wine style, early fruit thinning at levels that are “luxuriously” low has a big effect on alcohol levels, but it can have a slight effect on other aspects of wine style too. If you think about the shift in style in Bordeaux (or Napa Valley) from the '80s to the present, higher alcohol, blacker color, and darker fruit character have become routine. Some suggest global warming is to blame, but you can just as easily make the case that this is the result of fruit thinning. Global warming is undoubtedly involved, but my take is that the widespread embrace of fruit thinning is probably even a bigger factor. And high end vineyards are continuing to thin even more in an effort to differentiate themselves.

For an effect on wine flavor—physiologically pushing the fruit into a riper spectrum—fruit thinning has to be done very early, well before veraison. The process is ideally conducted by seed hardening, which occurs halfway between bloom and veraison, and signals the beginning of ripening (ripening starts well before color change—veraison is just one stage in the process). If done later in the season it will increase sugar accumulation in the remaining fruit, but in my experience it won’t change the fruit character much. A loose rule of thumb for fruit thinning is that for every week after seed hardening 10% more fruit needs to be thinned to get the same result.

Pignolo in Friuli after fruit thinning

Merlot in Napa after fruit thinning

Color Thinning

There is another type of fruit thinning that can change wine character: color thinning. This is simply a sorting process, and it has no impact on the way the remaining fruit ripens. At veraison, fruit color change is not uniform; instead, the berries and clusters darken one at a time, over a period of time. It’s pretty standard practice these days in high end vineyards to try and create more uniformity by thinning off the lagging green clusters at the tail end of veraison. The idea is to get rid of the less ripe fruit, shifting the population of fruit into a riper spectrum. This has become a totally standard practice, and it’s another way that wine style has gotten less green and more ripe throughout the world over the past couple of decades. Incidentally, color thinning at the end of veraison provides a different result than sorting during harvest. By harvest, all the fruit has turned color, and there is no way to determine whether a given cluster is two weeks behind the pack without tasting it or sampling the brix. Optical sorters at the winery can only remove the extreme laggards, but not the fruit that is just a week or two behind the others.

Interestingly, a study by Mike Anderson at UC Davis showed that the fruit eventually catches up around 26° brix (26-28° brix is fairly standard these days in many parts of the world, which I find sad, because in my opinion that level of ripeness obliterates terroir by homogenizing wine style...but that’s another story). So color thinning is probably unnecessary for modern high-ripeness winemaking. If you leave the fruit out long enough, it will all get ripe. Of course, for someone trying to make that style of wine in California in 2010 or 2011, when early rains cut short the prospect of long hangtime, rigorous color thinning could have been a savior. Color thinning becomes a tool of risk management, an expensive form of insurance. When picking earlier, say around 23.5°—a pretty balanced ripeness level for a more classic red wine—color thinning can make a pretty big difference in the greenness and acidity of the wine, and that comes down to stylistic goals. For our wine, for example, we don’t perform any color thinning, because we want the freshness that is contributed by the slightly less ripe fruit. To summarize: color thinning eliminates some green character and lowers acidity for an earlier harvest date or cool climates, but doesn’t have a whole lot of impact if the fruit is given a long extended hang time in a warm climate.

Do Lower Yields Always Produce Higher Quality Wines?

When producers say that they “restrict yields,” assuming the work is done early enough or they are selecting the green fruit at veraison, the result is a shift in wine style. This is an “improvement” in quality if the goal is higher alcohol, darker color, riper fruit character, less greenness, less acid, and more concentration. If these are not desired attributes, then restricting yields can actually be a negative. It is well known, for example, that fruity, high acid wines, like rosés, are much better at higher crop loads. When I was working as a research viticulturist I did a number of experiments with Chardonnay and Sauvignon Blanc, and we always preferred the fruitiness and balance of the higher crop levels. The low crop levels showed unpleasant bitter and phenolic characters, higher alcohol, less acid, and less fruitiness. They did have more weight, though, if that is the goal. High scoring-type Chardonnay producers often thin the crop way down, emphasizing the phenolic character to intensify weight and finish while softening the wine with lees stirring and new oak.

Among European Biodynamic and “natural wine” producers, there is a move away from fruit thinning. Some of the Biodynamic producers believe that it interrupts the vines’ natural ripening process or “rhythm”, while some of the natural winemakers and other traditional or “old school” producers think that the mix of less ripe fruit with the riper fruit is an important part of the wine balance and longevity. The green, vibrant fruit contributes freshness, a critical part of wine balance. There is no doubt that wine from vineyards with no fruit thinning will often show less concentration, lower color, and higher acid. The aromas can be much more high-toned, though, with finesse and the distinctive freshness that one often finds in the wines of more traditional producers. If lower yields are necessary to achieve a minimum level of ripeness, these producers leave less buds at pruning rather than thinning fruit.

White grapes react very differently than red grapes to fruit thinning. Color and tannin are not issues. A heavier crop slows ripening, allowing more time for green characters to dissipate and for ripe characters to accumulate. White varieties can benefit from as heavy a crop as the vines can ripen by the end of the season. As mentioned earlier, the exception is when viscosity is a goal, in which case a low crop seems to work better. The modern, thick and heavy Chardonnay formula requires severe fruit thinning to increase viscosity and concentration, and a long hangtime, during which the acid drops and the sugar climbs to high levels. Balanced and fruity whites do better with the opposite approach. A big crop can slow sugar accumulation while fruit character develops.

Restricting yields by thinning fruit or limiting bud numbers at pruning can be critical in cold, marginal sites—without a severely low crop the fruit may not be able to get ripe. On the other hand, in hot growing areas it is important to have enough fruit on the vine to temper sugar production, so that the alcohol doesn’t totally dominate the wine. This assumes that there aren’t other restrictions on the vines, like low water availability. There is a three dimensional matrix between crop load, water and nutrient availability, and climate.

There is a point of diminishing returns with fruit thinning, no matter what the goals. The difference between 2.5 tons per acre and 3.5 tons per acre in the Napa Valley, where the vines could easily ripen 5 tons per acre to conventional standards of sugar and acid, is probably nil. Yet people insist on thinning to an extreme that makes no sense. I often feel that there is a “no pain, no gain” mentality, that through suffering one achieves greatness. Or, “if a little bit is good, a lot is better.” Beyond the wastefulness of thinning more than is necessary or advisable, there is a sustainability issue: vineyards are farmlands that have been taken away from nature. They are poor wildlife habitat. They need to be sprayed, cultivated, etc., and even organic sprays have an impact on the environment. So the lower the crop level, the more environmental impact per hectoliter of wine. That is the operative formula. Sustainability needs to be looked at per unit of wine, not per acre, and it is wasteful to throw perfectly good fruit on the ground. Cutting the crop in half is equivalent to doubling the diesel, pesticides (organic or not), and acreage under cultivation.

There is a trend in high-end winemaking towards thinning fruit to a level that has no scientific grounding. It causes grape growers and viticulturists incredible consternation. There is a constant tension in the business between the grape growers and the winemakers. When the grapegrower and the winemaker are the same person, this tension results in sleepless nights. Even with a decent understanding of the science it is difficult to determine exactly how much fruit to thin, or even to thin fruit at all. The current dominance of tradition and conformity muddies the waters tremendously. It is difficult to have an open discussion between vineyard and winemaking stakeholders about how much fruit to thin, and when to do it. Many winemakers feel incredible pressure to make wine that “wows”, and there is a great deal of fear involved in the process. Thinning fruit is one way they can assert “control” over the “quality”, and ease the anxiety a bit.

To summarize, other than in the case of a few Biodynamic and natural producers who don’t want to meddle with the natural ripening cycle of the vine (and a good number of viticulturists like myself who question the wastefulness and resulting high ripeness levels), most winemakers would agree that moderate fruit thinning is a standard modern practice in almost all cases. Thinning the fruit from the weak vines, the weak shoots, defective or diseased fruit, really green fruit, bunched up fruit, and heavily loaded vines, is universally accepted, and more about farming and managing vine health than wine style. Further fruit thinning to reduce yields far below the “balance” level (which I define as the point at which the vines can easily ripen to 13-15% potential alcohol), if done early enough, may result in darker, more concentrated, and riper wines. Ultimately, this marks a change in style, but not necessarily quality.

Some Useful Conversions

1 ton per acre = 13 hectoliters/hectare = 2250 kilograms/hectare
1 ton = 5.6 hectoliters = 2.5 barrels = 60 cases

General Comparisons of Cabernet Sauvignon Yields in California

Napa = 2-5 tons/acre
Lodi = 5-8 tons/acre
Fresno = 8-12 tons/acre

Spring and Early Summer Canopy Management: Winemaking in the Vineyards

2012-07-20T11:52:00Z

Spring and early summer in the vineyards is when the wine is truly made. Springtime for a viticulturist is like fighting a war, or like surfing a huge wave, depending on whether you’re a man-against-nature type or you tend to eat mushrooms and marvel at its magnificence. Either way there is no question that it is the most intense time in the vineyards. Mother Nature deals her hand in the spring, and how the cards are played translates directly into the finished wine. There is always a battle for time and resources in the vineyards, so during the early canopy growth period the viticulturist has to constantly evaluate the vines and form a strategy, prioritize, and then execute—and then, of course, change everything the next day when the weather shifts. Spring and early summer is the most stressful time of the year in the vineyards—it’s a relief when the vines settle into their mid-summer routine. By the time harvest rolls around, there isn’t much to do but pick the grapes—long hours, but straightforward. Just one task, don’t screw it up. During the spring there are a million things going on at once.

The Rhythm of the Season

Before getting into the details of the spring practices I want to describe the seasonal context. Bruce Cakebread once described the inexorable march of summer days as the “drumbeat of the vintage.” The season thumps along at its steady rate, and we have to somehow sync the vine phenology to that drumbeat (“phenology” is the term used to describe the seasonal progression of the plant—budbreak, bloom, veraison, etc. are phenological stages). Wine quality is dependent on keeping up with the drumbeat. What you do is less important than when you do it. As the old saying goes, “the difference between a good farmer and a bad farmer is two weeks.”

A major part of viticulture has to do with syncing phenology to the season. It starts with selecting varieties and rootstocks for a certain site. Are we on the Sonoma Coast or in Calistoga? North-facing or South-facing aspect? Pinot noir will get ripe too quickly in Calistoga, whereas Cabernet sauvignon might never get ripe in Freestone. This is obvious, but the same thinking drills down to many little decisions, such as timing of pruning, cover crop regime, irrigation, trellis style, canopy size, irrigation, and timing and style of leaf removal. These all have subtle effects on phenology.

While walking a vineyard together, Warren Winiarski once told me, “the vines keep getting bigger until the summer solstice, and then they start getting smaller.” That simple little observation—something he had learned from Andre Tchelistcheff—is absolutely the case, and it describes the crux of the seasonal rhythm. The summer solstice is usually June 21st, and that date should mark the end of canopy growth. It also loosely coincides with hardening of the seeds, which is where berry growth stops and ripening starts. Continued growth of the vines after that date will severely impact wine quality—less color, less concentration, green characters, less ripeness. On the other hand, vines that stop growing too much in advance of the solstice are typically excessively stressed, and can show in the wine as hard tannins, lack of high-tone aromas, bitterness, and a general lack of “generosity.”

Part of the job of the viticulturist in the spring is to guide the vines so that they grow normally and on schedule and then slow down and stop around the summer solstice. This means that one has to watch the shoot tips all spring, constantly assessing whether they are growing too fast or too slow. If they are growing too fast, shoot-thinning can be delayed, soil cultivation can be delayed or forgone, weed control can be delayed (not forgone—meadow mice can attack the trunks if weed cover remains around them throughout the season), and any irrigation water or fertilizer can be withheld. If the vines are growing too slowly they can be shoot-thinned early to remove competition, watered, or fertilized; or the soil can be cultivated, and fertilizers and growth enhancers like seaweed can be included in powdery mildew sprays.

However, Mother Nature dictates the vintage: while we have quite a bit of control over vine growth, we don’t have much control over bloom date (other than choosing the variety and rootstock) and bloom is the most critical moment of the entire season. The shoots can be long or short, but bloom is going to happen when it is going to happen. Not only is it fraught with risk—rain, heat, cold weather—but the timing of bloom pretty well defines the timing of harvest. Most vineyards have a consistent number of days from bloom to harvest, and so the timing of bloom dictates the timing of harvest. A late bloom means a late harvest, and all of the fall rains, slow ripening, and lack of a post-harvest vacation that comes with that gloomy scenario. So in addition to trying to protect the bloom with sprays (organic or conventional), tipping the shoots if fruit set is an issue, and pulling tissue samples to send to the lab for nutrient analysis (to guide fertilization), the bloom date is always carefully recorded to predict harvest dates and compare seasons. Once the bloom date has exposed itself, we get back to managing whatever we can to keep the vines in good shape given the hand we were just dealt.

Annual activity timeline...with year round gopher trapping

Shoot-Thinning

After the vines wake up and budbreak occurs, which is typically in March or April, the first spring pass through the vineyard is for shoot-thinning, or suckering. This is a slow and laborious pass. It is our chance to correct any pruning errors, to follow up on the pruners’ strategy, and to again shape the vines, so it is a skilled operation. The basic principle is to leave one shoot growing from each bud retained at pruning time, and rip off and/or rub out everything else. With cane-pruned vines, this is also the time to select well-placed suckers in the head of the vine to serve as canes for the following year. The vines start out looking like bristle brushes, and at the end of the process they have nicely spaced shoots.

Shoot-thinning is such a slow process that it takes several weeks or up to a month to complete the entire vineyard(s). If it is done early then the retained shoots grow more vigorously. If done late then the shoots to be retained are held back. For this reason the weakest areas in the vineyard are always done first, and the strongest areas are done last. Timing of suckering is a key viticultural tool. Too early and you have to go back again and clean off the regrowth—but it is sometimes worth it if the vines are very weak and need that much of a boost.

Shoot-thinning affects the quality and quantity of the fruit set. For instance, two shoots often grow out of the same bud on a vine. If the vine is spur-pruned, extra shoots on each two-bud spur are removed, because only the two main shoots will give good fruit. With cane-pruning, if there is space on the cane and the crop looks low, you can leave the “double” shoot to get a bit more fruit, or to get more shading on the fruit. Since bloom hasn’t yet occurred during the shoot-thinning stage, we don’t know exactly what our fruit set will be, but we can already see the flower buds, so we can do counts and get an idea of what we have going into the season.

Shoot-Positioning

After shoot-thinning but before bloom, the shoots are guided into position on wires in trellis systems. If done correctly, the shoot tendrils will attach to the wires, and remain in place even during extremely windy conditions. This is an activity where timing is everything. It is imperative that the shoots are positioned straight up and down, and do not overlap each other. Floppy, piled-up shoots are a major cause of green flavors, poor acidity (high potassium in wine), poor color and poor ripening, as well as a pathway for disease problems. The green flavors, poor color, and poor ripening are due to blocked light; the poor acidity results from deep shade, causing shaded leaves to turn yellow and senesce, exporting their potassium to the fruit; and disease occurs because it is physically impossible to get sprays inside zones of such densely packed leaves.

Leaf or Lateral Removal

After the shoots are thinned and positioned, the next step is leaf or lateral removal. To define the terms, “leaves” are the main leaves on the shoot (one per node), and “laterals” are the mini-shoots that arise from the axillary buds at the base of the leaves. In California, where sunburn is a concern, we have moved to removing laterals to thin the canopy out a bit, but leaving the leaves for protection from the sun. In places like Oregon, where the sun is less intense and disease pressure is high, both leaves and laterals are removed.

Typically, leaf or lateral removal immediately follows fruit set (fruit set marks the end of bloom, when the berries that were fertilized stick on to the rachis, and the rest fall off). A few people do leaf removal before or during bloom to try to maximize light from day one. This is thought to decrease fruit set, perhaps from a wounding response, or possibly reduced carbohydrate nutrition due to the reduced leaf area adjacent to the flower—it’s not really known if or why bloom-time leaf removal reduces set. It’s done in places like Germany where they have tight clusters and very high disease pressure, so they want to reduce set and get a more open cluster. For the rest of us, though, since we don’t want to endanger bloom, we wait for the fruit to set and then remove leaves or laterals. Like shoot-thinning, this is a slow activity, so it can’t all be done at once; unlike shoot-thinning, the vigorous vineyards are done first, because they need the light and air movement around the clusters, and the weaker vineyards are done last, if at all.

Which leaves or laterals to remove is determined by the row orientation. The basic concept is that morning light is good, and afternoon light is bad. Hot afternoon sun on the fruit is to be avoided. Even if sunburn isn’t evident, the baking sun will leave reduced levels of anthocyanins and aromas in the fruit. Morning light, on the other hand, will stimulate the production of anthocyanins and aromas. So on East/West running rows, we thin out the North side, and on North/South running rows we thin out the East side.

On Northeast/Southwest running rows—the best row orientation in a warm climate as it balances the heat load on both sides of the canopy—it gets trickier. In this case, if the vines are balanced, you can do nothing; if vigorous, you can thin the leaves or laterals in the interior of the canopy, leaving a protective shell of leaf cover on both sides. I tend to leave the fruit zone alone, and thin laterals only a few inches up above the clusters, letting diffused light trickle down from above. Leaf and lateral removal is very particular to the individual viticulturist, much more so than the other canopy management activities. Most viticulturists have their trademark leaf removal method, and it’s a major point of contention between them. Driving by a vineyard you can often tell who farms it by looking at the leaf removal.

When the vines have an obvious cool side, the fruit can be quite exposed. If there is no obvious cool side then one has to be more careful. Either way, though, the upper portion of the canopy has to be addressed as well. In this case, the goal is not to adjust the light on the fruit, but to alter the entire canopy. If we have dense shade even after good shoot positioning we need to pluck out strong laterals until specks of light can be seen coming through from the other side. Richard Smart, who is a bit crude, describes a perfect canopy as one where “there are enough gaps in the canopy that you can peak through and watch a person undressing, but there are enough leaves that they can’t see you standing there watching them.” He’s a great viticulturist, but a bit creepy. Good image though.

Tipping, Topping, and Hedging

The most visual steps in spring canopy management are tipping, topping, and hedging. These activities are variations on the basic concept of cutting back the length of the shoots. Tipping is just cutting off the shoot tips, topping means cutting the shoots back quite a bit, and hedging refers to cutting back the sides. The perfect boxed-in hedgerow of vines is the result of topping and hedging. It is more than a visual postcard shot, though: there are viticultural reasons for the practice.

Tipping at bloom can be slightly effective in attaining a better fruit set (more berries per cluster). This is a big issue in varieties like Malbec or Merlot that tend to shatter at bloom. Removing the shoot tips diverts energy to the flowers. Also, in all varieties, tipping only the strong shoots but leaving the shorter weak shoots improves shoot-to-shoot uniformity by temporarily stunting the strong shoots, allowing the shorter shoots to catch up a bit.

Topping is typically done after bloom, when the shoots are starting to slow down. The goal with topping is to alter the leaf area-to-fruit ratio. Reducing the leaf area slows down sugar accumulation, reduces water usage, and limits carbohydrate storage for the following season, reducing vine vigor. These effects can be positive or negative, depending on the goals. Topping at a consistent height aids vine-to-vine uniformity as well, since both strong and weak vines are restricted to the same amount of leaf area.

Topping at 14 leaf nodes is fairly common in the Napa Valley, but considered excessive in parts of Europe, such as Burgundy, where 10 leaf nodes is more common. When production of tonnage is the goal, such as in Modesto or Fresno, 24 leaf nodes are common. A newer strategy for California is to top at 16 leaf nodes to provide the leaf area needed to fuel veraison, then to top again after down to 12 leaf nodes after veraison to reduce the rate of sugar accumulation. If the weather turns cool at veraison and we want more sugar accumulation, the vines can be left at 16 nodes.

Hedging the sides of the vines is tricky for the tractor driver—the knives of the hedger whirl dangerously close to the trellis stakes and wires—but it can skim off the outside layer of laterals on vigorous vines, improving the canopy microclimate and reducing leaf area that would otherwise be used by the vine to grow roots to be even stronger the following year.

Vines prior to hedging

Vines after hedging

Fruit-Thinning (Green Harvesting)

The two principal times for fruit-thinning, also known as green harvesting, are in the spring and at veraison. The purpose of spring fruit-thinning is to balance the crop load with the vigor of the vine by removing fruit from weak shoots and third clusters, and to eliminate clumping. This is the last of the main spring activities.

Before doing much thinning its important to figure out how much fruit is on the vines. An easy way to fail as a viticulturist is to surprise everyone by showing up on the crushpad with way more or way less fruit than the winemaker expected. The crop estimate is one of the core bullet points on the viticulturist’s job description. The winemaker needs to know how much fruit will be coming in so that they can plan for cooperage, and the owner is concerned with cash flow.

Shortly after bloom we count the clusters on a number of vines to get an idea of what we’re dealing with in each vineyard. The number of clusters per shoot varies quite a bit from year to year, depending on the weather the year before. This is because the grape cluster primordia—kind of like the embryonic form—actually form in the bud as it is developing on the newly growing shoot in the spring. To be clear, these are the clusters for the following year. Over the course of the summer those canes harden, they are pruned in the winter, and finally those buds push up in the following spring. If the weather was good the previous summer there will be two or even three large clusters on that shoot. If the weather was cold and rainy there will only be one or two smaller clusters.

The most common time to thin fruit is at seed-hardening (also called lag phase). This marks the time that the cells in the berries have stopped dividing, but haven’t yet started to expand prior to veraison in the course of their final ripening push. Thinning when the berries are still growing (before seed-hardening) causes the vines to compensate for the crop loss and make the berries bigger. If the vines are weak they should get thinned earlier to propel berry growth, but if the vines are strong then the berries can really blow up if thinned too early.

Bloom to Seed-Hardening: approximately 35 days
Seed-Hardening to Veraison: approximately 35 days
Veraison to Harvest: approximately 45 days

Thinning too late after seed-hardening can be a waste, since the effect of thinning fruit diminishes quickly as the season progresses, to the point that close to harvest 75% of the fruit needs to be thinned to get an increase in brix similar to thinning 25% of the fruit at seed-hardening.

Since seed-hardening is a predictable stage in the berry development, it is the next opportunity to guesstimate the crop size after bloom. We cut off 20 or 30 clusters and weigh them. The rule of thumb is that the berry size will double between seed-hardening and harvest. So we take our cluster weight and multiply by two. We already have the cluster count per vine from bloom-time, so figuring out tons per acre is pretty easy. This helps guides the severity of thinning. If the crop estimate is too low then we thin less, and if a bumper crop is expected then we thin hard. The goal is to achieve a normal-sized crop.

A vine prior to thinning

The vine after thinning

No matter how well we execute the pruning, shoot-thinning, shoot-positioning, and tipping, there are always a percentage of the shoots which don’t develop properly, and the fruit from these shoots is inferior. Typically these shoots are placed in two categories: if less than 18 inches in length all clusters are removed, and if less than 24 inches in length only one cluster is retained on the shoot.

One of the viticultural principles that most people agree on is that a shoot should have a maximum of two clusters. There is occasionally a third cluster on a vine, and that cluster typically doesn’t ripen properly. The varieties can really differ on their predisposition for excessive numbers of clusters: Petit verdot can produce up to five clusters on a shoot, whereas Merlot rarely produces a third cluster. Either way, removing any third clusters is a standard practice.

This is also the time to thin out clumps of fruit. No matter how good the job of winter pruning, there are always shoots that are too close together, causing the fruit to get bunched up. It is critical that each cluster has room to hang separately from the adjacent clusters. If fruit is clumped together, the clusters on the interior of the clump will remain pink and watery and be more susceptible to powdery mildew or bunch rot. The clumps need to be separated and thinned out before the berries swell and soften. If the clumps aren’t thinned in time, the fruit will get tangled together as it grows and be impossible to separate.

And that’s it. We’ll go over all of the spring tractor jobs, like spraying, mowing, discing, spading, weed control, and how they influence wine quality and character, at another time.

Steve Matthiasson makes classically balanced wines under the Matthiasson label, and consults on vineyard practices for a number of wineries, including Araujo, Spottswoode, Stag’s Leap Wine Cellars, Chappellet, Hall, David Arthur, Long Meadow Ranch, Limerick Lane, Duckhorn, and others.

Winter Pruning: The Devil is in the Details

2012-03-01T17:21:00Z

The devil is in the details. Viticulture, even more than winemaking, is an apprenticeship-based practice. The complexities are only hinted at in the handful of books on the subject. The science spans many different disciplines, and since the subject is as varied and inscrutable as Mother Nature herself, there is no sign any time soon of us truly understanding any of the myriad aspects of viticulture, which range from the inner truth of the grapevines’ genes, proteins, and metabolic pathways out to the huge forces of pests, weather and climate. Though we will never understand much of why things are really happening in the vineyards, humans have developed a tradition and a craft of viticulture through trial and error which dates back thousands of years, and that craft is what I am going to attempt to share with you over the course of the year. This will be the first of a series of detailed articles on viticulture, starting with pruning.

Pruning

Pruning is the foundation of viticulture, and it is not usually described very clearly. There is Guyot, cordon, goblet, or whatever, and that’s fine, they look different and are traditionally used in different places, but why are these different systems used, and how are they actually managed in the vineyard? This first article will attempt to break pruning down for you so that when you look at a vine somewhere in the world you will understand why it is pruned the way that it is.

The way the vines are pruned speaks volumes about the terroir of that site, and adds another dimension to one’s understanding of the wine. The head-trained vines of the Southern Rhone tell you something about the climate, while the cordon-trained vines of the Northern Rhone tell you something different about the climate there. The traditions didn’t evolve in a vacuum; they evolved due to the needs of the site. So the pruning gives insight into the wine.

cordon pruned vine at Silvio Jermann's estate in Friuli

Why We Prune Vines

The most important tool in all of viticulture and winemaking is the pruning shears. Unlike other fruiting crops, like apples or peaches, grapevines cannot shed crop on their own. By pruning a vine we regulate the amount of fruit that it will carry, assuring ripeness. Pruning also allows us to space the fruit out for sunlight and airflow. Pruning determines how strongly each shoot will grow, which profoundly impacts wine quality and style. With proper pruning there is little else that needs to be done to the vine for the duration of the season; leaf-pulling, fruit-thinning, trimming and hedging, and much of the spraying can all be reduced or eliminated with good pruning. Unfortunately, it’s very difficult to achieve proper pruning on each vine, but many of the problems that we deal with in the vineyard and the winery—disease, slow ripening, green character, lack of concentration or otherwise unbalanced wines—can be prevented with good pruning.

The main areas that we look at with pruning are the timing, vine balance, and vine architecture. These concepts supersede the different pruning systems, like Guyot, goblet, or pergola. The pruning systems are means to an end—different ways of accomplishing vine balance given the growth habits of the particular variety and the climate and soil of the specific terroir. So when it comes to pruning a vineyard, the first question is when to get started—the timing of pruning.

Timing of Pruning

The timing of pruning has major implications. Pruning can be done any time from harvest up to and even past budbreak—a four month window. The timing of pruning within that window has a number of different implications, so in the vineyards we put a lot of thought into when to prune.

Recently, there has been greater awareness of the biology of the wood-rotting diseases that are wreaking havoc around the world by drastically shortening the lives of vineyards. A number of these fungal diseases, such as Eutypa or Esca, infect fresh pruning wounds. The spores are dispersed by rain, and are exhausted over the progressive winter rain events, which means that the later the pruning, the lower the danger of infection. For this reason pruning dates have tended to be much later in the past decade or so than they used to be. Napa and Sonoma used to be pruned in December and January, whereas now most vineyards in both counties are pruned in February and March. Later pruning makes a big difference.

Pruning timing also influences the timing of budbreak—the later the pruning, the later budbreak occurs. Depending on the site, later pruning (such as mid-March) can delay budbreak by up to 10 days. If the site is susceptible to frost this can make a big difference (vineyard sites have different frost susceptibility because cold air rolls off the hillsides and sinks down and builds up in low-lying areas).

Given labor issues, though, not everything can be pruned at the last minute, so vineyards have to be prioritized. Also, late pruning can result in reduced spring shoot growth. If the spring is dry and the pruning is too late, the soil water can start running out before the canopy has fully grown. For this reason, dry-farmed vineyards are often pruned very early, even as early as December. Luckily, Zinfandel—the most common dry-farmed variety—is less susceptible to the wood-rotting diseases.

There is a slight effect of pruning date on harvest date as well—only a few days, but in a marginal climate, like in Oregon, or out on the extreme Sonoma Coast, a few days can make all the difference, especially when rain is forecasted.

The pruning date can have an impact on fruit set or shatter as well. French and British books refer to shatter as “couloure”: a bunch of berries fall off the rachis, or stem, and yields go way down. It’s a huge problem with grape-growing; Malbec and Merlot are notorious for it, and Pinot Noir and Cabernet Sauvignon can suffer some years, creating a big vintage variable. Depending on spring rains, early or late pruning, which results in early or late budbreak, can shift bloom one way or another by up to a week, potentially placing bloom in completely different weather. In general, there is less chance of spring rains with a later bloom, however there is a greater chance of heat, neither of which is good for fruit set. So the local weather risk has to be taken into consideration: is the vineyard on the coast with a lot of spring rainfall (better for late pruning), or in a hot interior region, with dry hot winds in the late spring/early summer (better for early pruning).

Balanced Vines

Once you decide on pruning date, there is the bigger question of how to actually prune the vines. “Pruning severity,” which basically describes how much of the vine is cut off and how much is left, may be one of the most critical factors in the entire season of the vineyard. Pruning severity is the main way that we create “balanced vines.” Balanced vines are everything.

Since grapevines are long-lived perennial plants, the potential growth of an individual vine doesn’t change much from year to year. They become fairly well regulated to their growing conditions and only change their potential growth slowly from year to year. This is partly because the carbohydrates that fuel the spring growth were stored the year before, and partly because the conditions where they are growing (rocky soil, deep soil, sandy soil, cool climate, hot climate, dry climate) don’t tend to change. In my way of thinking, grapevines just aren’t risk-takers—they pretty much just do the same thing each year. A vigorous vine will tend to be vigorous, and a weak vine will tend to be weak. So, staring at a leafless dormant plant with pruning shears in hand and assessing the way it grew the previous year is the first step in deciding how “hard” to prune it.

The goal is for each vine to grow a certain amount—not too much, not too little. Weak vines tend to make wine that is hard, thin, and lacking in generosity. Strong vines tend to make wine that is green, light, and insipid. If there is one point to be made in this entire article, it is that “balanced” vines tend to make balanced wines—literally thousands of years of viticulture have confirmed this. The Romans knew this, the monks in Burgundy knew it, and it is still the rule. Everything else being equal (soil type, climate, water availability, etc.), the best wine will be made from vines with proper balanced growth. If you were to weigh an individual cane it would be somewhere around 60 to 90 grams. It would be almost as thick as a Sharpie at the base and as thick as a pencil two feet out. It would stop growing naturally at around 40-50 inches. This is true in Châteauneuf du Pape and in the Mosel. Our goal with pruning is for each cane to grow just the right amount.

We can achieve vine balance by leaving the correct number of buds. Bud number is so important that most AOC regulations in France dictate it. Bud number is relevant because the number of potential new canes is determined entirely by the number of buds left at pruning. We leave more buds on a stronger vine to dilute the growth over more shoots, and we leave fewer buds on a weaker vine to concentrate the growth into fewer shoots. If we get the bud number right at pruning, both vines will have canes of equal length and girth, but the strong vine will have a lot more canes and the weak vine will have less canes: the number of canes is different, but growth for each cane is the same.

Here is where is gets a bit technical and geeky: the way we determine how many buds to leave is to count the canes grown by the vine the previous year. Imagine that two adjacent vines were pruned the previous winter to 16 buds. If one vine grew 12 normal canes and 4 weak canes last year, it should only get 12 buds this year when pruned: one bud for each healthy cane and no more. This growing season, everything else being equal (rainfall etc.), it won’t have any weak canes, and therefore will be more balanced. If the other vine grew 12 normal canes and 4 “bull canes” (overly-strong canes) then it should get 20 buds this year when pruned (doubling the number of bull canes and repeating the normal canes). It too will be more balanced, without any bull canes. Things should be done in the vineyards to strengthen the weak vines and subdue the strong vines, but that is a long-term strategy, and pruning needs to be used in the short term to restore vine balance.

This is one of the reasons that cane pruning provides more flexibility than spur pruning. A quick definition: “cane pruning” is the practice of leaving one of more canes, typically 5 to 9 buds long (e.g. Guyot) and “spur pruning” is the practice of leaving a certain number of two bud spurs along a cordon or on a head (e.g. goblet). There are pros and cons with each system, but there is no doubt that cane pruning is the best bet for balancing the vine.

Cane pruning gives the pruner tons of options: to leave just a short cane, a long cane, two long canes, multiple canes, or any combination thereof. Spur pruning can be flexible too, but not on an annual basis—canes can be altered every year, but once the vine is set up with spurs they are pretty well fixed.

Vine Architecture

Vine architecture, especially spacing, is the second most important principle of pruning after vine balance. It varies by variety, climate, and the economic realities of the production needs, but in general the goal is to prune the vine in such a way that no fruit is touching and the vine canopy will be even—no clumps or bare patches. This means that each shoot should about every four to five inches apart. Areas where the shoots are bunched up will result in clumps of fruit that are plagued with uneven ripening and fungal disease issues. In addition, clumped up leaves adversely affect fruit flavor and acid balance even if the fruit is thinned out and well-spaced. Shaded leaves will turn yellow, dumping their potassium into the ripening fruit, which kills the acidity, causing tartaric acid to precipitate with the potassium as an insoluble salt. Fanatical attention to light distribution is one of the ways my own Matthiasson wines have high natural acidity without green characters. It’s not rocket science or slight-of-hand, its just good pruning.

Bare patches in the canopy caused by excessive spacing are problematic too. They expose fruit to direct sun, which robs aroma and color through overheating of the fruit, or they may even cause sunburn, which contributes bitter and prune-like characters to the wine. It also means that you get less fruit—gaps in the canopy here and there add up over the entire vineyard.

Good spacing is one of the main virtues of spur pruning—cane pruning may give you better vine balance, but spur pruning gives you better shoot distribution. The vines are trained when young to have their spurs spaced six to eight inches apart. You have to carefully moderate the growth of the young vines to get them to grow that way—if they grow too fast they get leggy, and the spacing is too wide.

After that the trick with spur pruning is to maintain the proper spacing: we’re dealing with mother nature, and the spurs tend to wander around over the years; the pruner has to select spurs each year that maintain or improve the spacing.

Here is where we get geeky and technical again, but bear with me so I can explain how to spur prune. Since two canes grew out of each two-bud spur from the year before, there are two choices per position (each spur location is called a “position”), an upper cane and a lower cane—either can be cut back to two buds for the spur. The other cane gets cut off. To keep the position from climbing too high over the years, the lower cane is typically chosen for the spur and the upper cane is cut off. Occasionally, though, for better spacing, an upper cane is turned into a spur and the lower one is cut off. If there is a big gap next to the position, both canes from that position can be left as spurs creating a “rabbit ear.” If two spurs have grown too close together, one is cut out entirely. The pruned vine should have a nice even distribution of spurs all the way along it.

The downside of cane pruning is spacing. Mother nature gives us buds that are unevenly spaced along the cane, and everything is bunched up around the head of the vine (the “head” is the top of the trunk where all the canes sprout out from).

The first part of dealing with spacing on cane-pruned vines is selecting the cane. We’re looking for a cane that has buds spaced three to six inches apart. If the buds are too close some of them can be cut off to space them out. Selecting this cane can be tricky, because it also needs to be round (not flattened—that means it was poorly nourished), have received plenty of sun (this is important for fruit production), and be in a good position to be bent over and wrapped onto the wire without breaking.

The second issue is to figure out how to deal with the head. Cane pruning typically involves leaving one 2-bud “replacement spur” in the head area for each cane. This is to assure that there will be a cane for the next year in the right place, and also a spur to continue the process for the following year. This is a simple concept but it can be hard to explain. The process is this: the two-bud spur grows two shoots; they are cut back to one cane and one spur; the next year the cane is cut off (it has born fruit and has now outlived its usefulness) and the two shoots coming from the spur are again cut back to one cane and one spur; the following year the cane is again cut off and again the previous year’s spur is cut back to a cane and a spur…and the cycle continues annually.

Leaving a cane and a spur works great with a traditional Guyot, wherein you leave one cane and one spur. The cane grows out one direction and the spur grows out the other direction. It’s a great system—it’s used in most of Burgundy—but the vine vigor has to be low enough so that just one cane can handle all of the growth. If there is too much vigor (back to vine balance) you need to leave two canes, and with one spur per cane the head of the vine is now totally congested and screwed up. There is no physical space for the spurs and both canes all coming out of one single head. This is a big deal, and it is where a lot of cane pruning goes wrong.

An example of a single Guyot vine, with cane and spur, at Grands Echézeaux

An example of a Double Guyot vine (two canes and no spur) at Littorai

With two canes it is best not to leave spurs, a much more advanced viticultural technique reserved for high-end vineyards. The selection of the replacement canes for next year must be done when the vines are suckered in the spring. All vines have to be suckered every spring, but instead of just ripping through it, the person doing the suckering has to be sure to leave the two replacements from the head—or the next year there won’t be any good canes for the pruner to select. With no spurs the finished vine should have an even spread of shoots along its entirety, with no extra density at the head or the ends of the canes.

The third main training system, and one that I absolutely love, is head pruning. Head pruned vines are tough to manage, they are an inefficient use of vineyard real estate, and they are only suited to varieties with an upright growth habit and good fruitfulness on spurs instead of canes. Nonetheless, head pruning is a fantastic system for a warm climate and for varieties with large clusters.

The two main systems for head training are the vertical cordon and the goblet. The vertical cordon is more common mainly because it’s easy—and that’s the only thing it has going for it. Basically, you just run the vine up a stake and leave spurs up and down the trunk. It creates a shaded and non-uniform canopy. You see it a lot in California, and much less so in Europe, where the pruning tends to be better. The goblet is the way to go. It takes a few years to develop, but is well worth it. The spurs are trained out like a wagon wheel, ideally spread out to a diameter of a foot and a half or so, and all on the same vertical plane. Diffused light reaches all of the fruit, and the clusters are not in a glob. One of the beautiful advantages of the goblet is that spurs can easily be added or taken away to balance the vines, unlike in cordon pruning. Yet the vine benefits from the nice spacing and regular shoot growth that you get from spurs.

Next installment: “Springtime in the Vineyard”