31 May 2010
Although the bloom on a grape's skin contains healthy wine-making yeasts, less desirable wild yeasts and bacteria are usually also present, brought to the grape either by insects, or carried aerobically - that is, by the air. If the wild yeasts are allowed access to the grape juice, the sugar is converted into alcohol much too quickly and the yeasts wear themselves out before the alcohol content is high enough. The partially made wine is then vulnerable to assault from the bacteria, which makes it sour. The wild yeasts and bacteria, therefore, have to be kept out of the process altogether. The principle way of achieving this is to keep the juice or 'must' away from the air, since both wild yeast and bacteria need oxygen to survive. This can be done either by conducting the fermentation in a sealed tank or by dousing the 'must' with sulphur dioxide, which feeds on all the local oxygen.
The wine-maker can also regulate the length of the fermentation period by controlling the temperature. As anyone who's made wine or beer at home will know, the cooler the temperature, the longer it takes for the yeasts to complete their job; and broadly speaking, the longer the fermentation period, the more delicate and subtle the resultant wine. Before sophisticated equipment was designed to control the temperature of the 'must' during fermentation, you could predict, as a general rule, that the hotter the wine-making area, the poorer would be the quality of the local wine. Now there is an abundance of new technology available to wine-makers which can overcome most local handicaps and, consequently, the general quality of even the cheapest wines has improved.
But however streamlined and advanced wine-making aids may have become, the end product, wine, can only be as good as the ingredients that go into it. It's like cooking. Essentially, you can't expect perfect results if you use sub-standard ingredients. And where wine-making grapes are concerned, there are a great number of different factors that radically affect quality. The most important, of course, is the variety of the grape, but since grapes consist largely of water, this accounts for only part of it. The water content of grapes is derived from the earth in which the vine plants its roots, so geology plays an important part. And since the critical ripening of the grapes depends on the weather, the situation of the vineyard and the sort of climate it enjoys are other vital considerations as well.
On the face of it, these details may seem far-fetched and remote; further proof that a lot of fuss and nonsense is made about wine. If you are any sort of gardener at all, however, you will know that even, say, a tomato will thrive or wilt depending on exposure to sun, the supply of water and the type of soil. To look more directly at the effect of the elements on the quality and taste of specific fruit, you can simply take apples as an example. From England you get the Cox, a small, highly scented apple with a sweet, strong flavour, which gradually acquires its relatively intense character over a long, slow growing period, with only intermittent bouts of sun From areas with hotter climates, such as the South of France, you get the comparatively woolly Golden Delicious, which puffs up quickly under ceaselessly coaxing rays of hot sun. As far as flavour and quality are concerned, a lot of sun is altogether too much of a good thing. It brings on the fruit too quickly for it to be able to acquire much in the way of flavour and character.