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Viticulture


Overview: go to article

Introduction
Viticulture is the science of growing grapes.

Climate
The world wine producing zones lie between 30° and 50° north and south latitutudes.
Climate is the general long-term weather pattern for a region.
The Heat Summation System defines growing regions of grapes based on temperature.
Frost can damage vines in early spring as well as the plant's dormant period.
Hail is unpredictable and can easily damage vines.
Heat stress slows down photosynthesis in the vines.
Poor weather can lead to coulure and millerandage.

Soil
The type of soil and components found within it determine how well grapes grow.
Organic viticulture uses natural means to rid the grapes of pests.
Terroir, the French word for earth or soil, is used to describe all the attributes which combine to make one location different from another.

Vine Species
Vitis vinifera is the scientific name for the most common grape used in winemaking.
Crossings, hybrids, and clones are methods viticulturists use to produce new varieties of Vitis vinifera.
Phylloxera is the insect that accounts for more lost crops of grapes than any other pest.

Pruning and Training
Pruning and training the grapes is done to control and support grapevines during growth.

Vineyard Annual Chart
A chart on the annual cycle of grapevines summarizes what is done at the vineyard month by month.


Viticulture

The Article back to top

Viticulture is the science and practice of grape growing. People engaged in this business are called viticulturalists or are sometimes referred to as grape-growers or even vine-growers. Their practices vary tremendously around the world and are influenced by the local toppography, the climate and soil. Many of their practices affect the grapes that are eventually harvested to make wine, like soil preparation, choice of vine variety and rootstock, vine density, vine pruning and trellising, irrigation, control of pests and dieseases, and methods of harvesting. This section will look at the important issues of viticulture including climate, soil, vines, pruning and training, trllising, organic viticulture, and harvesting.

Climate back to top

Vines grow in a wide variety of climates throughout the world and continue to expand to new regions and climates. Vines and grapes do not like extremes of temperatures and so, for the most part, are located in the temperate zones between 30° and 50° either north or south of the equator. Vines have difficulty growing above 90° F and below 50° F. Winter frosts below -15° F can also stymie vine development. Vines also do best where there is a dormant period of about six months. In the Norhtern Hemisphere, the most northerly zones for growing wines is around 52° N which is the latitude for British Colombia and Southern England. In the Southern Hemisphere, the most southerly wine growing region is about 46° S in Otago, New Zealand. A look at the digram below shows the bands of climates condusive to vine-growing. You may realize that there is still great potential for grape growing throughout the world in areas including Eastern Europe, parts of the former Soviet Union, and China. In any case, the best quality grapes are grown where there is a relatively long and cool ripening period.

While climate, or macroclimate, is generally understood to be the general, long-term weather pattern of any given region, two related terms should be specified. The word mesoclimate is used to refer to the weather of a specific site. It encompasses the influence of local topography and so would refer to the weather of a particular vineyard or contiguous vineyard of similar aspect. Microclimate is usually reserved for the climate in a very restricted place such as a specific row or section of a row of vines. Some experts even confine a microclimate to within the area immediately surrounding a vine's canopy. Generelly, when a vineyard is planted, not only is it important to look at the macroclimate, but site preparation and desing should take in to account the mesoclimate and, perhaps the microclimate.

In order to compare wine regions around the world, various systems have been developed so that these comparisions have a scientific basis. In the United States, a common method for comparing the temperature of wine growing areas was devised by and is name after Albert J. winkler of the University of California. This system, which is sometimes referred to as the Heat Summation System, measures monthly average temperatures above 50 F for the growing season (below 50° F the vine does not grow). Winkler delineated five growing regions based on the temperature findings:

Winkler's Heat Summation System
Region I (the coolest) the best for dry tables wines of light body (Carneros)
Region II the best for dry table wines of medium body (Stags Leap)
Region III the best for full-bodied dry and sweet wines (Calistoga)
Region IV best for fortified wines
Region V best for table grapes and drying grapes

While this system has proven successful and is widely used in California, it is not fully accepted elswehere because in other regions, such as coastal Australia and New Zealand, temperature alone is a poor indicator of viticultural climates.

One climatic condition that affects the vine similarly throughout the world is frost. It is mainly a problem during the springtime but can also hurt dormant vines during the winter. Ice can form in the plant tussue of buds, young shoots , or leaves which will turn brown and die. Moisture in the wood may freeze, crackin or splitting the trunk, which could lead to loss of the entire vine. this is particularly true of late frosts that occur after teh sap has already begun to rise in the vines. There are many methods to prevent frost damage. Wind machines, such as the lare motor-driven propellers widely used in California, circulcate warm and cold air through the vineyard. heaters and oilburners are used to rasise temperatures. Another method is aspersion, or sprinkling water over the vines. the release of latent heast as the water freezed on the vines protects the vine tissue from injury.

Hailstorms are a thoroughly unpredictable climatic problem for which there is little relief save for taking out a costly insurance policy. Hail can strip a vine of its leaves, break off shoots, or damage the young fruit. Even though methods have been tried, like firing rockets carrying silver iodide into the cloud formation in an attempt to convert the hail to rain, no reliable method has yet to be developed to prevent this kind of damage.

Vines can suffer heat stress, which happens in areas where daytime temperatures approach or exceed 100° F. This is true in many areas of California, Spain, and Southern Italy. High temperatures cause photosynthesis to slow or stop, reducing levels of malic acids in the grapes. Heat stress, as well as sunburn, is fairly easily controlled through canopy management.

A region's climate is relatively fixed, but its weather may vary from year to year. Ideally, heavy rainfall during winter replenishes ground water reserves and is followed by a mild spring which encourages budbreak and successful flowering. Poor weather, notably cold, cloudy wet days, at flowering time can cause what is known as coulure. Coulure is when low temperatures cause incomplete fertilization and the unfertilized flowers drop off reducing the ultimate size of the harvest. Coulure is typically followed by millerandage where improperly fertilized flowers stay on the vine but fail to expand and swell into full size grapes. This leads to irregular ripening and perhaps a lengthy and difficult harvest. Rain at harvest time can cause rot, so most growers hope for a dry harvest season.

Soil back to top

Vines grow in many different types of soils, the variations of which are among the many factors that affect the quality of wine. Vines thrive in some very inhospitable and seemingly arid soils, stretching their roots deep into the sub-structure. Heavy clay soils should be avoided because vines do not generally do well where there is poor drainage. More importance should be placed on the organic content of the soil which in most cases needs to be replenished yearly. In order to grow proplerly, vines need the correct level of fertilizers in the soil, which means measuring and adjusting levels of magnesium, postassium, nitrogen, and other minerals.

Replenishing the soil with these and other nutrients is increasingly being done through organic viticulture. While its practice has many definitions, organic viticulture generally implies growing grapes without synthetic fertilizers, pesticides, or other growth regulators. Only microbiological products from plant, animal or mineral substances ar applied to the soil. In California, an organic wine must abide by the California Foods Act of 1990 and be labeled as such. It may also be certified by the California Certified Organic Farmers (CCOF). Other states are following suit and in France it's either Nature et Progrès, Terre et Vie or the UNIA -Interprofessional National Union of Agrabilogy - that oversees organic viticulture. It's important to note that, for American wines, there is a difference between "organically grown and processed" and "organically grown grapes." The latter term reflects the usage of sulfites. Sulfur is used in winemaking as an anti-bacterial agent and as an anti-oxidant. Sulfites do occur naturally though, and so the warnings on labels are directed at the less than 0.4% of the population that may be allergic to sulfites.

The relationship of soil quality to wine is not fully understood. It's generally agreed upon that the supply of water through the soil is one of the most important factors and that good drainage is important. Generally, vines do well in gravelly soils, that are moderately deep. It can be concluded that soil characteristics do influence the wine's quality and its character, but to what extent is uncertain.

Some viticulturalists place more importance on a vineyard's site and soil than others. They support the concept of terroir. The French term which literally means "the soil or the earth," is used in the world of wines to describe the marriage of soil, climate, and the grape variety planted there. An example would be the gravelly soil, cool maritime climate and Cabernet Sauvignon in the Médoc. Riesling, the slate soil and the cool, continental climate of the Mosel, is another example. In the New World, terroir may not have had great support in the past , but is becoming increasingly important.

Vine Species back to top

One of the most common vine species is Vitis vinifera, which literally means "the wine vine." Vitis is the genus and vinifera is the species. There are other wine producing species of grapes, such as Vitis labrusca, Vitis riparia and Vitus repestris. However, it is Vitis vinifera that accounts for more than 99% of all the wines consumed in the world. It is native to Europe as well as East and Central Asia, but it has been planted all over the world. There are estimated to be thousands of varieties of this species, some of the best known being cabernet sauvignon, chardonnay, chenin blanc, merlot, pinot noir, riesling, sauvignon blanc, syrah, and zinfandel. Each variety of grape has its own idiosyncrasies and contributes different qualities to wine.

New varieties of Vitis vinifera can be produced and they are called crossings. This is done by fertilizing the flower of one variety with the pollen of a different variety, followed by the planting of the resultant grape seeds and seedlings. The attempt is to garnish the benefits of both varieties. Few crossing have attained any prominence although some are important. Müller-Thurgau is a crossing that combines the quality of Riesling and the early ripening of Silvaner. Kerner is a crossing between Riesling and Trollinger and Pinotage is a crossing between Pinot Noir and Cinsault.

A slight variation on a crossing is a hybrid, sometimes referred to as an interspecific crossing. This is the offspring of two varieties of different species. Catawba is a a good example of an American hybrid coming from the parents Vitis vinifera and Vitis labrusca. Hybrids have little commercial viability.

Viticulturalists are constantly trying to imporve their crops and so may uses certain clones of a particular variety to achieve optimum quality. Clonal selection is the practrice of selecting a superior plant from a vineyard and taking cuttings from this vine for propogation. Typical cuttings or buds are taken from the mother vine, grafted onto rootstocks, and planted out for assessment. In this way varieties can be altered to suit particular circumstances. An example of a clone is the wine Brunello di Montalcino, which is made from a grape that is a clonal selection from Sangiovese. California's Gamay Beaujolais is a clone of Pinot Noir.

Phylloxera back to top

Phylloxera is an insect that damages the roots of some species of vine especially Vitis vinifera. It's a small, yellow aphid that has caused more damage to the wine business than probably any other pest or disease. Phylloxera is indigenous to eastern North America and was probably exported to Europe in the 1860's when American rootstocks were being used to combat powdery mildew. For nearly fifteen years it devastated the vineyards of Europe until it was discovered that the Vitis vinifera varieties could survive if they were grafted onto American rootstocks. Vineyards in California are now suffering a similar epidemic. Viticuluralists there have discovered that the widely used rootstock AxR1 is not as resistant as previously believed. Only a few wine growing regions - Chile, parts of Australia and New Zealand - have not been affected by phylloxera.

For more about Phylloxera click here or here

Pruning and Training back to top

The Grapevine is a true vine that requires some form of support to keep it off the ground. In the wild, tendrils along the canes attach to other vegetation and allow the vine to grow up off the ground. In our intensive cultural systems, there is no natural support for the vines. Therefore, we have to erect various trellis systems to train and support the vines, and facilitate other management practices.

Pruning can be defined as “the removal of plant parts to obtain horticultural objectives”. These objectives include:

-Controlling the size & form of the grapevine.
- Optimize the production potential of the grapevine.
- Maintain a balance between vegetative growth and fruiting.


Training can be defined as “the arrangement of plant parts spatially”. This is done to develop a structure that:

- Optimizes the utilization of sunlight and promotes productivity.
- Adapts to the characteristics of the grape cultivar.
- Promotes efficient & sustainable vineyard management practices.
- Is economical to establish and maintain.


To have productive grape vines that produce quality fruit, the vines must be trained and pruned to a definite system. Compared to other fruit plants in your garden, grapes are pruned rather severely. To properly prune a grape plant, you must understand some basic terminology pertaining to grapes:

Arm or Cordon-- short branch of wood extending laterally from trunk;
Cane-- one-year-old fruiting wood;
Cane bud-- located at a node on the cane, it produces the fruit shoot;
Internodes-- the portion of a stem between two nodes;
Node-- joint on a shoot or cane where buds and leaves are located;
Renewal spur-- a cane pruned to two buds;
Shoot-- current season growth of wood from bud, produces leaves, flowers, and fruit;
Spur-- a cane pruned to four or fewer buds;
Sucker-- a shoot that develops from the lower trunk or from under ground.


Knowing the fruiting habit of grapes is essential to properly understand grape pruning. Buds on one-year-old dormant wood (canes) produce next year's shoots on which the fruit clusters or bunches develop. Each shoot produces from zero to four or more bunches. There are many training systems for grapes. Each has its own advantages and disadvantages. In addition, some systems are better adapted for one cultivar of grape. While the four-cane Kniffen system is probably the most widely used training system for American hybrid grapes, there are other training systems that are probably superior. The Single Curtain Cordon system, either High or Low wire, is probably the best single training system for most of our grape cultivars.

To download a pdf file with more information about pruning and training grapes click here.
You will need Adobe Acrobat to open this file. If you need to download Adobe Acrobat click here.

Harvesting back to top

 

The timing of the harvest depends primarily on the ripeness of the grapes. Weather conditions at the time of harvest are also very important because rain or dampness can lead to rot. Beofore the main harvest, a thinning out may take place to remove unripened green fruit. Ideally grapes are harvested at the optimun balance between sugars and acidity.

Vineyard Annual Cycle back to top

 

Various factors affect the actual timing of vineyard operations. In warmer areas they take place weeks before cooler regions. Harvest can take place, depending on the variety and location and desired style of wine, anywhere from the end of August to the end of November. This is, or course, for the Northern Hemisphere. The vines cycle in the Southern Hemisphere is similar but takes place with a difference of six months. The cycle shown here is for the Northern Hemisphere.

 

January Pruning of the vines starts.
February Pruning continues.
March Pruning should be completed. Trellising is prepared. Annual fruiting canes are tied down. Sap begins to rise. Land to be planted should be prepared. Buds begin to appear.
April Buds break and growth starts. Frost protection is a must. Flower formation takes place. New vineyards are planted.
May Growth increases. Clusters of flowers form. Frost is still an issue. Shoot thinning takes place. Pest and disease control starts.
June Early varieties start to flower. Growth continues. Soils are tilled to control weed growth.
July Flowering is complete. Grapes start to expand.
August Veraison occurs, the transformation of the berries from small, hard, and green to swelled, softened, and colored.
September Grapes start to sweeten and acidity drops. Pest and disease control must stop four weeks before harvest. Some leaf trimming is done to expose grapes to sun and wind to keep disease, mostly botrytis, to a minimum.. This also speeds harvesting. Harvesting of early varieties begins.
October Harvest continues.
November Harvest is completed with the exception of some late harvest varieties. Final soil tilling is completed.
December Pruning may begin where vines are dormant.