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Viniculture1... 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.

vineyard photo.Grapes are the largest fruit crop on earth2. 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.

There are multiple and interlacing factors to consider when starting a vineyard, in order to ultimately Steep hillside vineyard scene.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 are Vitis sylvestris ("wine bearing vine of the forest") or Vitis vinifera (cultivated for wine). The Muscadinia subgenera 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.

How Many Bottles Grow Here?
Vineyards vary in the spacing of the rows and also between the individual vines. Depending upon age and variety, some are more productive per vine than others, some produce larger clusters of fruit and some yield more juice per pound of fruit. Wine makers and their facilities also vary in the amount of juice they are willing or able to squeeze from the grapes. So, in rough averages, keeping the variables in mind ...

How Many ...?
GRAPES per ...
500 - 750
180 - 275
360 - 550 K
2 - 25
1 - 9
2 - 18 K
... per BOTTLE
... per ACRE
3 - 18 K
4 - 24 K
2 - 12

A Cluster averages 40-60 grapes;
a Pound of grapes averages 4.5 Clusters;
a Ton of grapes averages 60 Cases of wine;
a Bottle of wine averages 2.75 lbs of grapes.

Vinifera grapes are not very juicy, but have uniformly tender pulp, easily removable seeds and firmly-adhered skins. They also tend to be high in acidity and lower in sugar. Properly pruned vinifera vines develop on short stout trunks, capable of sustaining heavy loads of ripe fruit. More than 90% of the world's grapes, including those for raisins, table use, and wine, are from this single species.

In the subgenera Euvitis, native American vine species include labrusca (northern fox grape), aestivalis (summer grape), riparia (riverbank grape), rupestris (hillside grape) and others3. All have slow-growing vines and slender stalks, requiring trellising for support. Compared with vinifera, these species are very tolerant of cold temperatures, but have insignificant crop value. Only the Vitis labrusca variety Concord is commercially important.

American native grapevines also make up the entire the subgenera Muscadinia, with only two species: rotundifolia, most prevalent throughout the Southeast, and Munsoniana, confined to Florida. These are commonly known as "slip-skin" varieties, for their readily-detachable skins cover juicy, somewhat tough central pulps with firmly embedded pips (seeds). As with the other native American grapes, their vines are also slow-growing and weak. Muscadinia varieties have acquired natural immunity to Pierce's disease.

In the Northeastern U.S., V. labrusca grapes (Catawba, Delaware, Niagra, etc.) are used to make wines of limited regional popularity. Concord (V. labrusca) is almost singularly used for the commercial production of jam, jelly, and juice, along with sweet wines that have some popularity nationally. In the Southeastern U.S., V. rotundifolia grapes (Muscadine, Scuppernong, etc.) again make wines or primarily local interest. Hybrid grapes (Baco Noir, Seyval Blanc, Vidal Blanc, etc.) created from cross-pollinating European and American varieties, attempt to gain both the flavor characteristics of the former and the weather-hardiness of the latter, with some success.

Wine made from native American grapes (i.e., Vitis labrusca, V. rotundifolia, etc.) is quite distinctive with a "wild" or "foxy" flavor that tends to be an acquired taste for most people. The essential wine value of native American vines comes not from their grapes, but from their roots (especially V. riparia and V. rupestris), which are naturally resistant to the deadly louse phylloxera vastatrix.

Although vines could grow from the fruit seeds (or pips), the seeds do not turn out exactly like the either of the parents. For example, seeds from a Chardonnay grape would not necessarily grow into a Chardonnay vine, because of pollination variables.

Wine grape vines are primarily hermaphroditic (with both male and female flowers), but the grape blossoms of one vine could be fertilized by the pollen of a separate vine, not necessarily of the same type. 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. Even an isolated mono-varietal vineyard's seeds will degenerate over time, developing problems from the inherent in-breeding of self-pollination.

Only two methods of grapevine propagating are practiced. Layering buries a section of a year-old cane, still attached to the mother vine and leaving the tip exposed. The cane will establish its own roots over a season and can be detached to form a separate plant. Vineyardists traditionally used this method to fill in rows where gaps occurred from disease or destruction. The other method is by cutting the cane first, then rooting it and transplanting it in a new location. Either practice means that virtually all cultivated grapevines are clones, and therefore identical to the donor parent. Only mutation will cause a cloned vine to change characteristics.

By selecting to propagate vines with desirable characteristics, such as vigor, fruit-bearing capacity, grape skin color or thickness, berry size, cluster size, early or late ripening tendencies, disease resistance, etc., the Vitis vinifera vine has been very highly bred over centuries.

Most modern wine vines begin as a cutting from healthy plants. 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 layering was allowed. Normal practice of the time was to 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 vineyards typically had an orderly, row by row appearance.

A parting of the rows on a hilltop vineyard.

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 spraying 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.

A nearly-ripe syrah cluster seeks refuge behind bird netting a few days before harvest at Alban Vineyards.Deer, raccoons, possums and other mammals 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.

All growers share the most fearsome danger to their ripening crop of grapes: birds. Birds cause the most crop loss and fruit damage to 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 reflective strips to nets to randomly-firing auto cannons, recorded sounds of predator birds, actual trained hawks, and laser shows.

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. In the Northern Hemisphere, this activity may occur anytime from November to March depending upon the local climate and weather.

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 a grow in a particular shape. It is a skill that requires experience and judgement 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 secateur.

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.

Pruning a head trained vine.

Just before the beginning of warmer weather, while the ground is often still muddy from Winter snow and rain (note the attire), workers use pruning knives or shears to trim back nearly all of the previous year's vine growth.

This photograph was taken in Sonoma County in 1942. The practice and methods, using secateurs or vine clippers, are much the same today as they have been for centuries anywhere on planet earth where grapes are grown.


Photo courtesy of Fleet Irvine Photomurals.

Pruning vines in 1942 (illustration).

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. In France, a single cane with a single spur is known as Guyot simple pruning and two canes and spurs as the Double Guyot, because Dr. Guyot was so influential in promoting these methods.

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.

Grapevines proceed through several stages of growth annually. The success of many vineyard operations, from pruning to harvesting, depend upon recognizing the characteristics and noting the timing of these growth cycles. Indicators of these cycles include bud break, flowering, berry set, and veraison.

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. Overhead sprinkler frost protection.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 to 50°F, bud break may begin the vegetation growth cycle as the green shoots emerge through the brown, dried bud scales of the previous season and the leaf tips appear. 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 reaches 60-65° F, the flowering will begin. An early flowering often 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. A good fruit set provides the grower with both optimism for a successful crop and options to focus on quality rather than quantity.

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. How well balanced the crop load is per vine can determine if some fruit thinning or "green harvesting" is needed in an attempt to boost quality.

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.

Scarecrow on vineyard guard duty. 

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. Keeping bird populations at bay becomes increasingly difficult. 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.

In 1935, researchers from the University of California at Davis began to investigate wine quality and compare climatological history. They classified each growing area of California as a Region, based on heat summation data. Grape vines are only physiologically active above 50° F. The degree days are the total of the average daily temperatures above this point. Grapes need at least 1700 degree days to reach maturity. Region I is coolest at less than 2500 degree days; Region II has from 2501 to 3000; Region III, 3001 to 3500; Region IV, 3501 to 4000; and Region V, over 4001. This information helps growers select appropriate varieties to match their climate.

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.

Perfect Season.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, however is not simply a 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, while total acidity decreases4.

Phenological ripeness develops desirable flavors. 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 often mixed with fertilizer and spread over the vineyards. Soil may be plowed back up around the vine-bases where necessary for protection from freezing. In the northern hemisphere, vines are dormant from November to March. 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.

Jim LaMar

The Sonoma County Grape Growers Association runs an excellent site with several articles that provide information about growers and appellations within Sonoma County, and grape farming issues in general.

You may be daydreaming about "How to Buy a Vineyard?" - this article on the Bergman Euro-National site answers many questions and provides examples of what to expect.

Science & Wine is the BLOG of Assistant Professor Paula Silva of the Institute of Biomedical Sciences at the University of Porto, where she agglomerates articles, research papers, and other science communications, as well as posting calendars of conferences, seminars, and workshops related to scientific studies of wine.

1. While the generally accepted word for grape farming is viticulture, raising wine grapes has so many aspects that differ from either table grape or raisin farming, that this new word should be adapted specifically for wine grape farming - VINICULTURE (other cultures use it already - try searching the web)! RETURN

2. Mangoes are now the second largest crop (as recent as 2003, bananas had that distinction - could this have been where the term "Second Banana" originated?)! RETURN

3. Botanical genus Vitis has two subgenera with distinct vine and fruit characteristics: Euvitis (considered "true" grapes) and Muscadinia. There are less than 60 known Vitis species. A great many of these are native to Eastern and Southern North America, including (Euvitis) V. aestivalis, V. amurensis, V. arizonica, V. berlandieri, V. candicans, V. champini, V. cinerea, V. cordifolia, V. doaniana, V. labrusca (including Concord varieties), V. lincecumii, V. monticola, V. Longii, V. riparia, V. rufotomentosa, V. rupestris, V. solonis and (subgenera Muscadinia) V. rotundifolia and V. Munsoniana. Only two species (Euvitis), V. californica and V. girdiana, are native to California. RETURN

4. Photosynthesis slows and shuts down at temperatures over 95° F although sugar accumulation can continue. Cool nights, periods of rest are important to fruit that becomes distinctively flavored, not simply sweet. RETURN




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