Viticulture: The Science of Wine
The term “viticulture” refers to the art and science of growing grapes. Viticulture is a branch of horticulture. We use the term more specifically to refer to the agricultural production of wine grapes.
Left to its own devices, a grapevine will snake its tendrils around any vertical or horizontal support it can find: a tree, a wall, a fence. The vine prefers to head upwards, towards the enriching light of the sun. Its aim is to use the energy of the sun to produce leaves. To the vine itself, the leaves are the gist of the plant. The tendrils of the vine from which the leaves spring have an impulsion to take over as wide an area as possible. The vine, however, is not content to take over a limited geographical area. It wants to colonize non-contiguous areas. For this purpose, it creates sweet and tasty grape berries which contain seeds. Its hope is that animals will eat the desirable fruit, and spread the durable seeds elsewhere in their droppings, in the process perpetuating the species.
This is how nature wants it the story to play out, but humans are in charge of viticulture. For humans, the entire process revolves around the sweet grape. Humans know that some attention must be paid to the sunlight-absorbing leaves, but only in a proper balance with the grapes. The aim is to expose the foliage to the sun for sufficient photosynthesis without excessive shading of the grapes. Shading has the potential to impede the ripening of the grapes. Shading can also promote grape diseases, particularly those caused by a fungal attack. The grower will use “canopy management:” manipulating shoots, leaves, and fruit for the betterment of vine and fruit quality.
If any of this seems contrary to nature, well…it is. Grapevines are among the least natural of all agricultural products. One reason we have already discussed: most vines are grafted to custom-engineered rootstock. Further, commercial grapevines do not reproduce sexually through the promulgation of their seeds. As with humans, sexual reproduction gives unpredictable results. Cloning may be the stuff of science fictions with humans, but it is standard procedure with grapevines: asexual reproduction through vine cuttings is the norm. If the desired new vine will be reasonably close to the original vine, the grower may use a process called “layering,” which requires bending a vine and burying the ends into the soil. The vine will eventually grow upwards out of the soil, using the nutrition system of the original root while it gradually develops its own root system.
The grower wants to use cloning to create the most efficient and profitable vineyard possible. He or she has two choices. In clonal selection, the grower identifies the ideal base plant from an existing vineyard or from a nursery and uses that single plant for all cuttings. In massal selection, the grower takes cuttings from several different vines in a vineyard that has shown desirable traits. Massal selection is the traditional system. Many critics of clonal selection believe it discourages genetic diversity and results in wines that are predictably dull.
After drastic pruning in winter, vines are precisely trained and groomed throughout the growing season. It is all human action. The only “natural” option the grower has is to use sustainable systems of pest and disease control, but even here the human manipulates nature.
Vine Training Systems
Scores, perhaps hundreds of vine training systems are used in the world of wine, depending on climate, soil, vineyard aspect, grape variety, and, in many areas, tradition. Vines are tamed using stakes, posts and wires collectively called “trellises.”
The Annual Cycle of the Vineyard
The months used here are for vineyards in the northern hemisphere. Southern hemisphere vineyards are six months ahead. We say “ahead” because harvests in the southern hemisphere take place early in the year, in February, March or April, making a southern hemisphere vintage in any given year approximately six months older than the corresponding northern hemisphere vintage of the same year.
January and February is the time for winter pruning. Pruning in winter gives the means of maintaining a training system, allowing the grower to select which wood (canes) of the vine will produce fruit. Grapes are primarily produced from one-year-old canes. This necessitates removing the previous year’s two-year-old fruiting canes or spurs. Some one-year-old canes are also removed to reduce yields and amp up quality. The grower wants to favor the growth of the most promising canes. The grower thinks ahead, striving to produce healthy shoots for the coming growing season as well as promising canes for the next fruiting season.
In spur pruning, vines keep one or two pairs of long canes (a permanent cordon) that run along a trellis. Each winter, the grower cuts back new canes that have grown along the permanent cordon to small shoots containing two buds, known as a spur. Come spring, the buds on the spur develop new growth.
In cane pruning, the grower selects two to four shoots (canes) from the previous season to train over the length of the trellis, removing all the other canes. In spring, new shoots sprout on the surviving canes.
In March, new vines may be planted from grafted cuttings.
March may also see the beginning of bud break. The tiny buds on the vine begin to enlarge and bleed out liquids that rise from the roots. Soon after, the buds push out shoots, For the energy to do this, the vine uses reserves of carbohydrates (stored in the roots and trunk of the vine) that have been created the previous growing season. The buds will then sprout leaves that will commence the process of photosynthesis, producing energy to facilitate further growth.
May is the time the environment warms up enough to facilitate flowering. Most grapevines are hermaphroditic, meaning they self-pollinate, just around this time. The result is a tiny grape berry, the result of a process called fruit set. The process of fruit set does not always go well. If coulure occurs, berries fail to form properly and may prematurely fall off the vine. In millerandage berries form with uneven sizes, leading to problems later with uneven ripening and unpredictable grape juice quality. Malbec and Grenache have a particular sensitivity to coulure, Gewürztraminer and some Chardonnay clones to millerandage.
Despite the name fruit set, the grape berries at this stage are tiny, green, hard, high in acid, and have very little sugar. The grower hopes now that spring will bring weather that is warm enough to promote fruit growth. An unfortunate spring frost at this time can ruin the fruit. Growers use many methods of frost protection: everything from smudge heaters to helicopters designed to circulate air. If all goes well, within forty to fifty days after fruit set the berries will have doubled in size and will go through a process call (from the French) veraison sometime in July or August. English speakers pronounce the word “ver-AY-zon.” It is important not to confuse this with Verizon, which is a telephone company.
Veraison signals the beginning of the grape ripening process. At this stage, the grapes take on their expected color. The biological color change works like this: chlorophyll in the skin of the grape berries is replaced by anthocyanins in the case of red or black grapes or by carotenoids in the case of the green or golden grapes that make white wine. The color change does not occur uniformly in all grapes on the bunch, resulting in brief multicolored effects. In the case of grapes of all colors, the berries start to become softer, the grapes become sweeter as they build up fructose and glucose, and the acidity in the grapes begins to decrease.
Once the bunches of grapes have fully changed color, the grower might want to thin out less promising looking bunches to reduce the yield and allow a greater proportion of vine resources to go to fewer bunches. This quality move is called green harvesting.
The period of tension now begins for the grower: determining when to harvest. Harvest usually occurs in September or October, depending on climate (but global warming seems to be pushing harvest, and in fact all warmth-related vineyard processes, earlier and earlier). Electronic equipment can measure acidity and sugar level in a grape, but ultimately the determination of harvesting time is a judgment call. In an ideal scenario, the grower will harvest when the grape sugars have increased to an optimal level and the grape acidity has decreased also to an optimal level. Flavor compounds and phenolic compounds like tannins must also be considered. And yet, even if the grower gets all these factors spot on, two great uncertainties loom. One is the possibility of autumn rains, which can compromise a harvest and promote fungal diseases. The second is the availability of labor. Grape picking, like all vineyard and winery work, is skilled labor, usually furnished by teams of migrants from other countries (in the case of both the United States and Europe). It is ironic, perhaps, that many of those who issue blanket criticism of immigrants continue to purchase and enjoy wine—perhaps, for consistency’s sake, they ought to favor other beverages.
After harvest, the grapes are gone but the vine leaves remain. These green leaves continue the process of photosynthesis, creating reserves of carbohydrates that the vine stores in its roots and trunks. October is a prime period for this process, which will continue until enough fuel has been put into storage to get the vine through next year’s bud break and flowering stages. Once the storage process is complete, November perhaps, the grape leaves turn yellow and fall off, preparing the vine for its coming period of winter dormancy. The grower will leave the vineyard alone for a time, but then the pruning shears will come out and the cycle will begin all over again.
