Viniculture – Quality Factors For Growing Wine Grapes…
The grape vine is the source of all wine. Reaching the highest level of quality in wine is only possible by starting with the highest quality fruit. Maximizing fruit quality from any vineyard site can be a lengthy process, because the end results are revealed only after several seasons of comparison.
Grapes are the largest fruit crop on earth. The grapevine prefers the temperate climate in which it evolved, with warm, dry summers and mild winters. Winters of sustained cold kill grapevines. High humidity promotes vine disease. Tropical temperatures disrupt the normal vine cycle of winter dormancy.
Grapevines are fairly adaptable plants, growing in a wide variety of soil types, from light sand to packed clay, and flourishing around the globe in the temperate bands between 20° and 50° Latitude, north or south of the Equator. They are successfully grown in Europe, the Balkans, Asia, Mediterranean and South Africa, South Australia and New Zealand, most of North America and a good portion of South America.
THE BEST PLANS…
There are multiple and interlacing factors to consider when starting a vineyard, in order to ultimately achieve highest fruit quality. In selecting a site, the average length of the ripening season, the normal annual weather conditions, the soil type and chemistry, fertility and drainage, the topography, sun exposure, and likely pest problems should all be taken into account well before the first vine is planted.
Various soil compositions have different benefits, dependent in part upon locale, such as fertility, acidity or alkalinity, heat retention and reflection, etc. Clay, gravel, limestone, rock, sand, slate and other types of soil can all support grapevines, but the one factor that all great vineyards share, in spite of their geological makeup, is good drainage. It”s important for the vines to get water, but vines will ripen fruit better if the water table is just within reach of the roots.
The sum of information will bear upon the decisions of vine variety, vine density, row direction and spacing, irrigation and frost protection methods, vine training system, as well as fertilization and pest control management. These in turn will affect choices in crop load, canopy management, harvesting, and pruning.
At each step in establishing and maintaining wine vines, the grower must evaluate and commit to a course of inevitable compromise between highest quality and practical economy. Yet the results of even the most carefully researched and executed decisions are ultimately at the whim of Nature.
Botanical classification puts grapevines in the Family Vitaceae, Genus Vitis, with subgenera Euvitis and Muscadinia; one subgenera cannot breed with another. Wild European Euvitis grapes areVitis sylvestris (“wine bearing vine of the forest”) or Vitis vinifera (cultivated for wine). The Muscadiniasubgenera exists only in North America, where also some V. sylvestris and several additional wild non-vinifera species grow. There are dozens of wild and cultivated species of genus Vitis, but only the European subgenera Euvitis (true grapes), cultivated species vinifera, produces fine wine.
Although there are over 10,000 documented varieties within species Vitis, about 3,500 are cultivated, yet only about 230 or so are even regionally significant in the world of wine and a mere dozen have become commercially popular and widely known to consumers. The study of classifying and identifying grapevines is called ampelography.
SEND IN THE CLONES
Although vines could grow from the fruit seeds (or pips), the seeds do not turn out like the either of the parents. For example, seeds from a Chardonnay grape would not necessarily grow into a Chardonnay vine. The grape berries that produced those seeds began as tiny blossoms that were fertilized by the pollen of another (not necessarily Chardonnay) vine. Like humans, the vine offspring would carry the genetic material of both its “mother” and “father” and share some of its parents” traits as well as blend some of the properties into its own uniqueness.
The Vitis vinifera vine has been very highly bred over centuries. The modern wine vine begins as a cutting from healthy plants, so virtually all cultivated grapevines are clones, identical to the donor parent. Only mutation will cause a cloned vine to change characteristics.
Vine cuttings are called slips or scions. These are usually grafted onto rootstock that has been specially cultivated to combine growth vigor with resistance to disease. They are then put into sand for one season. This is called bench-grafting. Once the graft takes and it becomes established as part of the vine, the scion is often referred to as the fruiting wood or bud wood, as differentiated from the rootstock.
Some vineyards are planted using the cultivated rootstocks directly and, after one season to establish the root system, are then field-grafted with the selected fruiting variety scions. With either method the new vines are carefully nurtured to create a root system and develop a strong, woody stalk for the first two to five years after planting, without bearing a crop.
Young vines with shallow root systems are particularly vulnerable to floods, drought and fertility. If the surface soil is not too wet, too dry, or too fertile, the roots will grow deeper and wider in search of nourishment. Good drainage is important to establish and sustain stable, healthy vines.
After the roots and stalk have developed, the untended vine would grow wildly, spending most of its energy on spreading its shoots and tendrils. If left to nature, a single vine could cover as much as an acre of ground, with the roots developing wherever the branches touched earth. In ancient times, this was allowed, a practice called layering. Normal practice of the time was to online casino prop up the vines to prevent the fruit from rotting or rodents from eating it. The Romans even planted elms in the vineyards, simply to support the vines. These ancient viticulturists came to realize that, instead of allowing the vines to grow outward in all directions, training the vines in rows with canes pointing upward produced better, more even-ripening grapes. It wasn”t until the recommendations of Guyot, however, and the massive replanting due to phylloxera that vineyard typically had an orderly, row by row appearance.
ENEMIES AT THE STAKES
There are many pests and diseases that can attack and kill grape vines. Red spiders, moth grubs and various mites, bugs and beetles can all prey on the plant above ground. Most of these may be controlled with either sulfur sprays, or by newer “green” methods, such as introducing predacious insects and protective cover crops between vine rows.
Often the ends of vine rows are planted with a single rose bush. Insects, mildew and fungi seem to prefer the sweet smell of roses, which perform a “canary in a coal mine” function for grapevines, providing early warning of the need to treat for pests or diseases.
In climates with summer rainfall, molds such as oidium, mildew, white rot, grey rot and black rot may be prevented by regular sprayings of a solution of copper sulfate, slaked lime and water (Bordeaux mixture). Research is ongoing into biological methods of controlling these fungal problems.
New vineyards are particularly susceptible to destruction from gophers and moles. There are many methods of control and eradication, including attracting predatory raptors, trapping, poisoning, flooding and even a device that implodes burrows.
Some animals can consume a lot of fruit, damage more, and even harm the vines, especially young plants and shoots. Vineyard fencing usually serves to keep these larger animals at bay.
By far, birds cause the most crop loss and fruit damage in most vineyards. Vineyards located on barren land may fare reasonably well, but those near forests or that share the landscape with trees are prime avian feeding grounds. From the first days of veraison, all manner of controls are tried, often in combination, ranging from randomly-firing auto cannons and other noisemakers, to scarecrows and flashy streamers. The problem can even extend to wineries, should bins of harvested fruit get backed-up, waiting to be processed.
PRUNING FOR BALANCE
With time, it was discovered that better-quality fruit will grow on vines that are pruned back to distribute the bearing wood evenly over the vine. So, in the winter months, when the leaves have dropped and the vines are empty of sap, they are pruned back almost to the main stem.
Pruning is an art of delicate balance; too much will cause small, uneconomical crops; too little will cause over-cropping and low-quality fruit. Pruning also facilitates cultivation, disease control and harvesting, when the vines are trained to grow in a particular shape. It is a skill that requires experience and judgment and cannot be done by machine. There are only two basic pruning methods: cane-pruning and spur-pruning, also known as head-pruning. The tool used to trim the canes or shoots is a vine clipper or secateurs.
Spur-pruned (head-pruned) vines are usually found in older vineyards. Spurs are the canes (branches) trimmed back to only a pair of buds. Each bud will become a shoot which grows to a cane that bears the crop. In the winter after the harvest, the top cane is removed and the bottom cane trimmed back to a two-bud spur.
Spurs are often distributed around the head of the vine, like spokes around a wheel. The top is left open for sun-exposure and this method often leaves the vine in somewhat of a “goblet” shape. These vineyards can only be hand-harvested. Some head-pruned vines are converted after a time to grow on trellis wires. Head pruning is used only in warm growing regions, because it encourages massive vegetation that slows ripening. It also makes harvesting more difficult.
In the cane-pruning method, from one to four, one-year-old canes, each with six to fourteen fruit buds, are trained along trellis wires. This is also referred to as “cordon” (French for “arm”) pruning, since the vine looks as if it is stretching out it arms. Because one-year-old canes must be used to bear the fruit each year, the cane-pruners therefore must train the current fruiting canes and at the same time consider which spurs to train for next season”s fruiting canes
Modern trellising methods vary by variety, geography, geology, harvesting methods and winemaking style! Two-, three- or four-wire, vertical, lateral, cordon and other configurations of trellis may exist in neighboring vineyards. There are stakes made of wood, metal and those combining the two materials. Home vineyardists and winemakers often train vines on garden trellis, to please their aesthetics as well as their palates. The different materials and configurations primarily affect exposure to sun and wind and the accessibility of fruit clusters to specifically facilitate either hand or machine harvesting.
A VINE FOR ALL SEASONS
As Winter ends, the pruning is nearly finished and the growers take cuttings to make bench-grafts and root them in sand. They also begin cleaning and repairing tractors and machines that they will be using all spring and summer. It is also time to order Bordeaux mixture needed for spraying as protection against mildew and other diseases and pests. As spring continues, the vines emerge from dormancy. Sap begins to rise and brown sheaths, which have covered the buds, fall off. Now comes the first working of the soil, deeply, to aerate it. If the vines” bases were covered for frost-protection, they are now exposed. The remnants of pruning are burned and any rotten vine-stakes replaced.
With daytime temperatures starting to warm, bud-break may begin the vegetation growth cycle as the shoots emerge. Frost danger is now at its height. Smudge-pots, wind-machines, and frost-protection sprinklers must be repaired and readied. The soil is worked again to keep down the weeds. Suckers are removed from the vines about every ten days to encourage the sap to rise in the vines. Cover crops are sometimes planted between the rows to keep down weeds and act as hosts for predator insects.
When the daytime temperature increases, the flowering will begin. An early flowering usually signals a very good quality vintage. The warmer and calmer the weather, the better; rain or hail can be disastrous now. After flowering, the shoots are thinned, the best shoots tied to the wires. Within a few weeks, the blossoms are replaced by minuscule berries that will grow in size, but stay green and hard.
In damp climes, spraying with Bordeaux mixture begins midsummer. Some vineyards pull or remove leaves from around grape clusters to improve air circulation and reduce the possibility of bunch rot. Where weeds have been allowed to grow between the rows, they are plowed or hoed. Long shoots trimmed every two to three weeks to concentrate vine metabolism on the fruit.
About mid-Summer, comes veraison, the onset of ripening as the grapes begin to soften and swell significantly, while green varieties turn translucent and black grape varieties gain color. This signals the winemaker to prepare his equipment for the harvest. It is time also for diligent bird control in the vineyards.
The grapes now begin to sweeten as sugar is transported from the leaves into the fruit. The berries swell from increased water content that dilutes the concentration of the acids. Flavor compounds and tannins also begin to build. Monitoring the grapes will soon move from weekly to daily, anticipating harvest, as vineyard managers test sugar levels and winemakers taste for maturity and ripeness.
DEGREES OF QUALITY
Varieties differ in the amount of heat required to mature their fruit. One-hundred to 120 days after flowering, the grapes should be ripe. The harvest may start mid-August in warm areas, to late-September in the coolest ones.
Sugar is measured in the U.S. using the Brix scale, which uses specific gravity to determine the percentage of sugar, by weight. Wine grapes are normally harvested between 19° and 25° Brix. From the 1960s through the 1980s, wineries often paid growers based on sugar content and the tonnage.
Fruit maturity is not, however a simple matter of sugar content. Acid content is every bit as important to quality and flavor and even more so to aroma constituents. Grapes will respire acid (especially malic acid) as they ripen and this loss is greater in warmer vineyard locations.
As grapes ripen, sugar, color and pH increase as total acidity decreases. For the highest quality wine, grapes need to develop aroma and taste characteristics that only result from physiological maturity and sugar-acid balance. Some signs of this maturity are the browning of the grape seeds (pips) and lignation, which is the browning and drying of the berry stems. But by far the most important indicator of maturity is the taste of the grapes.
Quality-oriented wineries now negotiate grape purchase contracts based on acres, rather than sugar level and tonnage. This allows the winemaker, rather than the vineyard owner, to decide how much fruit the vines will carry and when the grapes are ready to begin harvesting.
Picking and the crush usually continues for two to three weeks. When it is over, the grape skins from the wine presses are mixed with fertilizer and spread over the vineyards. Soil may be plowed back up around the vine-bases where necessary for protection from freezing. Cover-crops may be planted between rows to help prevent erosion. As long as the weather remains dry, any land scheduled for planting the following spring may be deep-plowed. The vines are now immune to nearly all harm except for an unusually severe and deep frost. When the ground is dry and the severity of winter weather past, pruning will begin again for the next season.
Article source: http://www.winepros.org/wine101/viniculture.htm