Sula Vineyards

Wine, broadly speaking, is an alcoholic beverage made by naturally fermenting the juice of fruits or berries. Used alone, however, the term generally refers to the alcoholic beverage made from grapes; wine made from other sources will usually be labelled as such (e.g. “apricot wine”).
The wine-making process at its most basic involves a series of relatively simple operations. Differences in technique depend on the type of wine being made: white, red, rosé, sparkling, sweet, etc.
In brief, after harvest, the first stage of wine-making is crushing the fruit to release sugars, which then undergo fermentation upon the addition of yeast. The stage at which the juice is separated from the skins – called pressing – occurs either before or after fermentation (for white and red wines, respectively).

The new wine produced thus is then put through various treatments to ensure clarification and stabilization, along with various other cellar operations collectively known as élevage, before the final step of bottling.

Yeast plays a critical role in wine-making. Yeasts are single-celled organisms that feed on sugar in order to multiply. In the presence of unlimited oxygen, they convert sugar to new yeast cells, carbon dioxide, and water. If the oxygen supply is restricted, however, as in a large container, after an initial multiplication stage, the yeast switches to a second metabolic process in which the end products are mostly ethanol – potable alcohol – and carbon dioxide. Along with these end products, yeasts also make several other attractive flavour compounds. Heat is another by-product of the fermentation process, which is why refrigeration is usually required to prevent the yeast from being fatally damaged. A second, softening fermentation called malolactic fermentation may take place in wines high in malic acid.

To minimize the new wine’s exposure to oxygen, it is either kept in wooden containers (in older wineries) or in modern inert containers such as stainless steel tanks. Many red wines and a small proportion of white wines are aged in barrels, either of new oak or other wood. Blending is carried out by selecting wines from different lots according to the producer’s aspirations, and finally, before bottling, the wine undergoes analysis to check that it is stable and up to standard.

Reference: J. Robinson (Ed.), 1994. The Oxford Companion to Wine. Oxford University Press.