The quality of grapes is defined by the balance between sugar, acid and phenolics such as anthocyanins, tannins, and flavour compounds. This essay will not examine the factors in establishing a vineyard, but rather the factors within the direct control of the vineyard manager in an existing vineyard that will affect the quality of grapes produced. The principal factors that will be examined are pruning, canopy management, yield reduction, soil management, water management, and pest and disease control.
Winter pruning is the first step a vineyard manager takes to create balance between leaf surface area and fruit volume to enhance fruit quality. Over-cropping stresses the vine causing weak growth and incomplete ripening. The vine compensates for severe pruning with vigorous vegetation causing shading and hindering ripening of fruit. During winter pruning, vines are cut back to a specific number of buds based on the variety, climate, site fertility, style of wine, possible legal restrictions and volume goals. French Camp Vineyards uses the Oxbow system (a two row, tow-behind tool carrier) to mechanically prune and farm 600 vineyard hectares of mostly quadrilateral spur-pruned vines. Vines are pruned to yield 220 hl/ha for wines that sell for under $8 a bottle. Manual pruning used to cost French Camp vineyards $0.40 per vine; with the Oxbow system it is now $0.15. (Wines & Vines Magazine) Querciabella has quite other goals for their premium Chianti Classico. Vines are manually pruned to yield 35 hl/ha of grapes with high aroma and tannin concentration. In Champagne high concentration of phenolics are not a desirable quality factor and although yield restrictions are set annually and have been as high as 83 hl/ha in the past (Stevenson, World Encyclopedia of Champagne), in 2010 yields were set at 10,500 kg/ha which translates to approximately 68 hl/ha. Generally, a total pruning weight of 1/5 to 1/10 the crop weight is ideal. A vineyard manager with a volume goal of 50 hl/ha may prune to 80 hl/ha as a sort of insurance policy, waiting until after fruit set before making further crop thinning decisions. The vineyard manager will also keep an eye on timing of pruning depending on whether or not it is a late or early ripening variety and to what the climate risks the vine is exposed. In areas that are prone to spring frost, by postponing winter pruning to just before budbreak, flowering can be delayed to hopefully avoid frost during the pollination period.
The goal of canopy management is to promote the health of the vine and achieve full physiological ripeness of fruit with a good balance between sugar, acid and phenolics such as anthocyanins, tannins, and flavour compounds for the style of wine that will be made. A loose and well-aerated canopy and a ratio of around 10-15 cm ² leaf surface area per gram of fruit will not only enhance photosynthesis – it also helps prevent fungal diseases and potential nest areas for vine pests. (Sunlight into Vines, Dr. Richard Smart) Techniques involved include shoot thinning and positioning, leaf removal, and crop thinning. Canopy management affects not only the current year’s crop; it affects the amount of sunlight on developing buds and determines how fruitful they will be the following year. Canopy management actually begins in spring with shoot positioning on the trellis. In vineyards of the Veneto region of Northern Italy that have problems with fruit set due to vigour, they have found that tipping young shoots before bloom changes the vine’s hormonal balance and enhances a better and more even fruit set. Phillip Frees of Vilaforté in South Africa removes leaves in the fruit zone of Sauvignon Blanc at fruit set, stating that sunburn is actually avoided by giving fruit a chance to adjust early and naturally to its sunny environment and undesirable grassy components in the final wine are eliminated. Likewise he has found that shoot positioning brings higher tartaric and lower malic acid with the same sugar content resulting in softer acid, more delicate fruit and improved mouthfeel. Gary Wood of Montana wines in New Zealand retrained his vigorous Sauvignon Blanc Vineyard to a split canopy which improved physiological ripeness of the grapes as well as increasing the yield enough to compensate for the investment in materials and labour necessary to make the change. In some regions hail can devastate the vine’s canopy, if not to the fruit and the entire vine itself. Wineries that can afford it in Mendoza, Argentina often invest in nets to protect their hail-prone vineyards when they can afford the investment.
Crop-thinning may also begin shortly after fruit set. Because Austria’s St. Laurent variety is so susceptible to coulure, the Juris winery in Burgenland cuts away half of each bunch of St. Laurent grapes just after fruit set to promote better ripening and prevent fungus with a more loosely set bunch. Juris owner Axel Stiegelmar prefers this to crop thinning post verasion stating that cutting away fruit so late wastes the vine’s energy whereas cluster division results in a higher skin to juice ratio with more flavourful grapes and riper finer tannins. In other regions and/or for other varieties, green harvesting is practiced as verasion begins. The initial abundance of fruit can result in smaller berries for some varieties such as Zinfandel. Less ripe or excess bunches are removed to channel the remaining sunshine and nutrients into fewer, smaller berries to concentrate flavour and enhance ripeness of tannins. Crop thinning is not necessary every vintage or in every climate for achieving the best quality grapes. As an example, looking at the past decade in Burgundy one sees that the 2005 and 2009 vintages, both rated with the highest quality, were also the highest yielding. At Domaine Grivot in Burgundy green harvesting of Pinot Noir is not normally practiced. Etienne Grivot states that if 20% of the crop is thinned, you don’t end up with 20% less juice, but 10%, thus increasing the juice to skin ratio and diluting grape flavour compounds and anthocyanin content derived from the skins.
Methods used to maintain or improve soil structure and vitality are important factors in determining the health of vines and the quality of fruit. Methods used include soil aeration, weed control, cover crops, and fertilization. After harvest the alleyways between the vine rows are ploughed for soil aeration and in climates with severe winter frosts, such as Columbia Valley, Washington this opportunity is taken to simultaneously heap earth up around the base of the vines to cover the sensitive graft joint from freezing temperatures which could kill the vine. In spring, the earth is ploughed back, fertilized (sometimes organic or bio-dynamic compost is added at this time) and the ground is levelled. This provides nutrients that will be brought to the vines roots by rain or irrigation in the spring before flowering to promote vine fruitfulness. Mineral elements that can be added are urea, potassium, phosphorus, zinc, boron and magnesium. Lack of enough nutrients in the soil may lead to stuck fermentations and poor quality wine. Too much fertilization can not only be detrimental to the environment, it can stimulate vegetative growth to such an extent that it is detrimental to the ripening of fruit and result in meagre, herbaceous wines. Excessive use of potassium can also increase pH which can cause difficulties in wine stability in vinification. After the first ploughing, the vines are desuckered to prevent the vinifera part of the vine from establishing its own roots. While expensive, some viticulturists will seed for specific legumes and other high-nitrogen plants which promote soil nutrients and aeration and desirable micro-organisms in the soil. Another aspect of cover crops that is advantageous to soil is their ability to attract beneficial insects and thus reduce the need for driving the tractor through the vineyard to spray, thus compacting the soil with heavy machinery. Ridge Vineyards found that money saved on insecticides and herbicides helped to significantly mitigate the costs of seeding for cover crops. The disadvantage of cover crops in low fertility soils is that they may lead to too much competition for nourishment with the vines and cause atypical ageing in wines. After fruit set is the time for mowing cover crops, or weeds in open-cultivation, and ploughing them into the soil, providing both aeration and vine nutrition. At this time again, non-organic vine fertilization may be added to the soil.
Just like nutrients, vines require water, not too much and not too little. In regions where irrigation is permitted, many vineyards have systems installed. Although flooding and watering via furrows have been used in the past and still are in some countries and regions, most modern wineries employ drip irrigation. Spray irrigation is used primarily only to prevent frost damage to buds and flowers in spring. Availability of water is crucial for vines during the budding and flowering stages, but after fruit set mild water stress is desirable. Too much water encourages vines to produce shallow root systems and vigorous canopies with large grape berry clusters that may not achieve sufficient physiological ripeness. On the other hand, severe water stress will shut down photosynthesis and the development of sugars and phenolic compounds in grapes. A balanced supply of water will depend on a variety of factors including rainfall and drainage properties of the vineyard. Modern drip irrigation systems in dry arid climates, such as at Cayuse Winery in Columbia Valley have computer-monitored sensors placed deep in the vineyard soil in strategic positions. In this way, Cayuse owner, Christophe Baron supplies the soil with moisture at necessary key times such as during flowering, fruit set and the onset of vegetation. Baron also practices partial root drying and restricts irrigation to the absolute minimum from verasion to harvest when no more shoot growth is desired and the plant’s energy should be devoted solely to ripening its fruit. In very wet, rainy climates or vintages there is little a vineyard manager can do. In the poor St. Emilion vintage 2002, Château Valandraud strived to keep its ripening grapes from swelling and becoming diluted from excess water by spreading plastic tarps over the soil. The wine was declassified as a result. Fertigation, the method of adding fertilization elements to the irrigation water, can be a more efficient and economical way of fertilization that that described above with soil management.
Pests and disease can be detrimental to grape quality and must also be controlled by the vineyard manager. Much prevention can be achieved through the promotion of beneficial insects with cover crops or with good canopy aeration through methods already mentioned above. Pests can harm the vine by damaging or consuming leaves, fruit and wood, interfering with photosynthesis, health of the vine and quality of fruit. Pests can also be vectors of viral and bacterial disease. With the use of pheromone traps the spraying of insecticides can be limited to sprays that target specific pests during shorter time frames. Fruit that has been damaged by birds or other pests is susceptible to acetobacter infections and bunch rot. The vineyards dedicated to sweet wine production at the Sepp Moser estate are located near Lake Neusiedl in Austria, which is also a natural habitat for a multitude of birds. Birds can not only damage fruit, large flocks can plunder an entire vineyard in just a few hours. 8 km of nets per hectare protect Moser’s vines from these large vineyard pests. The fungal disease oidium attacks vines and can survive over winter in buds and diminish fruit set, reduce yield, and delay ripening. Fruit infected by this mildew tastes mouldy. Oidium is generally prevented in conventional viticulture through spraying with sulphur, while organic producers such as Sepp Moser in Austria are advocates of fennel oil. Peronospera also attacks all green parts of the vine, especially young leaves. When severe, leaves will drop resulting in reduced photosynthesis diminishing sugar and anthocyanin production in grapes. The classic treatment is sprays containing copper, but these are only effective for around 10 days or until the next heavy rainfall. Because the heavy use of copper over many years can result in soil toxicity, the EU limits this to 6 kg per hectare for conventional viticulture and 3 kg per hectare for organic. Vineyard managers can install weather stations in the vineyard that monitor temperature and humidity to help minimize their use of copper. Spraying of potentially toxic substances is not done in the weeks before the harvest. There are many treatments available to the vineyard manager to combat pests and disease, which ones are employed will depend on legal regulations and the philosophy of the winery. Costs of potential damage and crop loss are weighed against the costs of prevention and control.
There are numerous factors within the direct control of the vineyard manger that will affect the quality of grapes. Whether for a high volume mid-market wine or for a super-premium icon wine, balance between fruit volume and canopy as well as balance of the vine in its environment are the basis for high quality fruit. High quality will mean different things for different wine styles, grape varieties, and targeted market segment of the wine to be produced. Pruning, canopy management, yield reduction, soil management, water management, and pest and disease control will all be adjusted to the climate, preconditions in the vineyard, and the materials and budget at hand. Once harvest arrives, the vineyard manager will work closely with the chief winemaker to coordinate picking and ensure that the grapes come to the crush pad in optimal condition.
Note: The essay above is written in study preparation for MW exams.