How to Make White Wine
HOW WHITE WINE IS MADE
It is not difficult to turn grapes into wine. The winemaker’s job is to transform the year’s freshly picked grapes into the most appetizing wine possible.
Yeast harbours enzymes. When those enzymes are introduced to sugar they turn it into alcohol – a process called fermentation. In any established vineyard there are thousands of yeasts floating about in the atmosphere, some of which are naturally to be found on the grapeskins. Inside each grape is a high proportion of water, sugar in quantities determined by its ripeness, acids, a wide range of trace elements and the pips. As soon as a grapeskin is broken, the yeast comes into contact with the sugar inside the pulp and fermentation begins. The yeast continues to convert the sugar into alcohol until either it runs out of sugar so that the resulting wine is dry, or it reaches its maximum alcohol production and can do no more, leaving some residual sugar in the wine. Very few yeasts can function in a liquid stronger than 16% alcohol, for example.
Man must have discovered wine simply by leaving freshly picked grapes in a container – an amphora perhaps? The weight of the grapes on top would have crushed the grapes at the bottom, the juice of which would rapidly have been converted into wine. However, this happy natural process is just a little too haphazard for today’s professionals. Wine and air is a potentially dangerous combination, for instance, as anyone who has left a bit of wine in a glass overnight will have noticed. The oxygen in the air acts on the wine, making it taste stale and ‘oxidizing’ it.
The modern winemaker has sufficient knowledge and equipment to leave as little as possible to chance. Nowadays he will often kill off all the yeasts occurring naturally, by judicious use of the winemaker’s antiseptic, sulphur dioxide, and introduce yeasts that have been specially cultivated to work as effectively as possible for the sort of wine required. There are also many ways of keeping the wine’s contact with air to a minimum. The whole process of crushing and fermentation can be swathed in a ‘blanket’ of inert, such as nitrogen, which will protect it from harmful oxygen.
When making white wine, he can choose from a range of sophisticated methods for eliminating the harsher, solid parts of the grape. Using one of the many types of press now-available, the juice is pressed out of the grape pulp with a degree of delicacy determined by the importance of avoiding any possible taint of astringency from the skins and pips. The harder the grapes are pressed, the more juice, and therefore wine, will be made, but the lower its likely quality. All the little solids that still remain in the juice are usually removed before the fermentation gets going, either by centrifuge or by allowing them to settle out overnight.
In the modern winery, white wines are usually fermented in closed vats made of an inert substance such as stainless steel. Though unromantic, it is hygienic and preserves the fresh fruit flavour so important in most white wines.
The fermentation process is very sensitive to temperature. Yeasts will not function if it is too cold, and they are not effective in extreme heat. This means that in cooler climates winemakers may have to heat the must, the fermenting grape juice, to get at least the first vatful started. Fermentation generates heat, however, so it is sometimes necessary to cool the must as it is fermenting. This is particularly important in the production of white wines whose youthful grape aromas are their most prized quality. The world’s winemakers still vary considerably in the temperature they think ideal for fermenting different grapes and will doubtless continue to do so. What is exciting for today’s wine drinker, however, is that, with the help of refrigeration coils and tanks which can automatically be sprayed with cooling waters, winemakers are able to control the length and intensity of fermentation by adjusting temperature.
Fermentation can be allowed to stop naturally, leaving residual sugar only if the grapes are very ripe. A more usual technique of making wine sweet, very popular in Germany, is to add sterilized unfermented grape juice to the finished dry wine. Fermentation can also be stopped by the winemaker, either by adding lots more sulphur dioxide or, a more sophisticated method, by suddenly chilling the must and then filtering out any organisms that could threaten to restart fermentation.