The importance of sound viticulture as a precursor to wines of excellence is unequivocally accepted as a truth in wine making companies worldwide.
More so than for beer is the belief held that it is not possible to make an excellent product unless there is similar excellence in the source of fermentable carbohydrate. Most wineries tend to grow their own grapes or buy them from nearby vineyards.
The ideal climate for growing wine grapes is where there is no summer rain, it is hot or at least warm during the day, there are cool nights and little risk of frost damage. The great grape-growing and wine regions are listed in Table 3.1. A benchmark figure for the yield of wine from one metric ton of grapes would be around 140–160 gal. As red grapes are fermented on the skins and therefore are less demanding in the pressing stage, the yield is some 20%
higher than for whites.
Vine
Grapes
Must
Newly fermented wine
Stabilised wine Picking
Crush
Primary/secondary fermentation
Stabilisation, maturation
Bottling ± maturation Sulphur dioxide
Saccharomyces
Fig. 3.1 An overview of wine making.
Copyright © 2005 by Blackwell Publishing Ltd
Table 3.1 Major wine grape-growing regions (1998).
Country
Wine production (thousand litres)
Grape production (thousand tons)
Italy 5.42 9.21
France 5.27 6.88
Spain 3.03 4.88
United States 2.05 5.36
Argentina 1.27 2.00
Germany 1.08 1.41
South Africa 0.82 1.30
Australia 0.74
Chile 0.55
Romania 0.50
Data derived from Dutruc-Rosset, G. (2000).
Fig. 3.2 Scion buds grafted on to the rootstock. Courtesy of E & J Gallo.
Wine grapes belong to the genus Vitis. Within the genus, the main species are vinifera (by far the most important), lubruscana and rotundifolia. Com-mercial vines tend to be Vitis vinifera grafter onto rootstocks of the other Vitis species. Of course within the species is a diversity of varieties (cultivars) – for example, V. vinifera var. Cabernet Sauvignon.
It takes approximately 4–5 years from the first planting to yield the first truly good crop of grapes. The scion (top) of the vine and the rootstock to which it is grafted (Fig. 3.2) must be selected on the basis of compatibility, one with the other and the combination with the local soil and climate. Other key issues that come to bear in viticulture are the availability of sunlight, depth of the soil, its nutrient and moisture content and how readily it drains.
Table 3.2 Some varieties of grape.
Type Example Comments
White cultivars
Messiles Sauvignon blanc Bordeaux. Green pepper and herbaceous notes Muscats Muscat blanc Raisin notes. Prone to oxidation, so often made into
dessert wines
Noiriens Chardonnay Widespread use globally; use in champagne production. Wines have apple, melon, peach notes
Parellada Catalonia. Apple/citrus notes
Rhenans Gewurztraminer Cooler European regions. Lychee characters
Riesling German origin. Rose and pine notes
Viura Rioja. Butterscotch and banana
Red cultivars
Carmenets Cabernet Sauvignon Merlot
Bordeaux. Tannic. Blackcurrant aroma Lighter in character
Nebbiolo Italy. Acid, tannic. Truffle, tar and violet notes Noiriens Pinot Noir Beet, cherry, peppermint notes when optimal
Sangiovese Chianti. Cherries, violets, liquorice
Serines Syrah France (n.b. Shiraz in Spain). Tannic, peppery aromas
Tempranillo Spain, especially Rioja. Also grown in Argentina.
Jam, citrus, incense notes
Zinfandel California. Also used for light blush wines
Some regions are especially susceptible to diseases such as Pierce’s disease and phylloxera (an insect that attacks rootstock and which is prevalent, for instance, in the Eastern United States but now also in California).
Vines should go dormant in order to survive cold winters. Cool autumn conditions with light or medium frosts allow the vine to store enough carbo-hydrate for good growth in the ensuing spring. There may be 500–600 or more vines per acre. New vines are trained up individual stakes in the first grow-ing season. Only one shoot is trained in each instance with the others begrow-ing pinched off. Pruning of vines takes place in winter months after the vines have proceeded to dormancy and the canes have hardened and turned brown.
It is important to match grape variety to the location and to the style of wine.
A variety may develop certain characteristics earlier depending on how warm the growing region is. Accordingly, when that grape achieves full maturity, it may have lost some of that character. Table 3.2 summarises varietal issues.
There is some understanding (though far from complete) of the chemistry involved in varietal differences. For instance, methyl anthranilate is found in Lambrusca, 2-methoxy-3-isobutylpyrazine in Cabernet Sauvignon, dama-scenone in Chardonnay (Fig. 3.3). For muscats there are terpenes such as linalool and geraniol and there are terpenols in White Riesling. Some of these are found in the form of complexes with sugars known as glycosides (Fig. 3.4). Yeast produces enzymes called glycosidases that sever the link between the flavour-active molecule and the sugar over time, illustrating the time dependence of flavour development in this type of wine.
Methyl anthranilate
2-Methoxy-3-isobutylpyrazine
Damascenone COOCH3
NH2
CH2 CH OCH3
CH3 CH3
N O N
Fig. 3.3 Some compounds responsible for varietal differences in wines.
Sugar – aglycone Sugar + aglycone
Examples of aglycones: terpenes and terpenols Glycoside
Glycosidase
For example, geraniol OH
Fig. 3.4 Glycosides and glycosidases.
Unless a soil is extremely acidic or alkaline or suffers from deficient drainage, the soil type per se is unlikely to be a major issue with regard to grape quality. Any deficiencies in nitrogen level will need to be corrected by adding N, avoiding excess so as not to promote wasteful growth of non-grape tissue or increase the risk of spoilage and development of ethyl carbamate.
The local climate also influences the susceptibility of the vines to infes-tation. If there are rains in summer months or if the vineyard is afforded excessive irrigation, there is an increased risk of powdery or downy mildew.
Excess water uptake by grapes can also cause berries to swell and burst, which in turn enables rot and mould growth. Over-watering leads to excessive cane growth and delays the maturation of the fruit. In regions where infestation and infection are a particular problem, it is likely that some form of chem-ical treatment will be necessary. Botyritis cinerea is common where summer rains are prevalent. Winemakers refer to it as grey mould when regarded in an unfavourable light but as ‘noble rot’ when deemed desirable. The contamina-tion leads to oxidacontamina-tion of sugars and deplecontamina-tion of nitrogen, as well as reduccontamina-tion of certain desirable flavours. However, the character of certain wines depends on this infection, for example, the Sauternes from France.
Of particular alarm in some grape-growing regions is Pierce’s disease.
This is caused by the bacterium Xylella fastidiosa and is spread by an insect
known as the glassy-winged sharpshooter. It is prevalent in North and Central America, and is of annual concern in some Californian vineyards. It appears to be restricted to regions with mild winters. The sharpshooter feeds on xylem sap and transmits bacteria to the healthy plant. The water-conducting system is blocked and there is a drying or ‘scorching’ of leaves, followed by the wilting of grape clusters.
Harvesting of grapes is usually in the period from August through September and October. The time of harvesting has a significant role to play in determining the sweetness/acid balance of grapes. Grapes grown in warm climates tend to lose their acidity more rapidly than do those in cooler envi-rons. This loss of acidity is primarily due to respiratory removal of malic acid during maturation. The other key acid, tartaric, is less likely to change in level.
Ripe fruit should be picked immediately before it is to be crushed. If white grapes are picked on a hot day, they should be chilled to less than 20◦C prior to crushing, but it may be preferable to pick them by night. However, this is not the same for red wine grapes as the fermentation temperature is higher. Fruit destined for white table wine is picked when its sugar content is 23–26◦Brix. Grapes for red table wine have a longer hang time. These values are selected such that there is an optimal balance between alcohol yield, flavour and resistance to spoilage. The pH values in these grapes will be 3.2–3.4 and 3.3–3.5, respectively.
Harvesting is increasingly mechanical. While more physical damage occurs, it can be performed under cooler night-time conditions which is desir-able, especially for white cultivars. Sulphur dioxide may be added during mechanical harvesting.
Payment is made on the basis of the measured Brix content of the fruit, measured by a hydrometer or, more usually, by a refractometer. A commercial specification will also state the maximum weight of non-grape material that can be tolerated (perhaps 1–2%) and that the berries should be free from mould and rot. For many winemakers, it has been decided that growing their own grapes is prudent. However, the buying in of some material from other suppliers does allow financial flexibility.
The structure of the grape is illustrated in Fig. 3.5. The main features are the skin and the flesh. The skin comprises an outer 1-cell deep epidermis and an inner 4–20-cell deep hypodermis, which is the origin of the colour and most of the flavour compounds in the grape. Sugar and acid are concentrated in the flesh. The sugar content may reach as high as 28%. Tartaric and malic acids account for 70% of the total acids in the grape.