The manufacture of wine varies in detail according to the type of wine to be produced, but it usually follows a standard pattern. The grapes are crushed and the grape must is allowed to ferment in vats, usually after the addition of sulphur dioxide. A selected strain of wine yeast may be added at this point. Heat is produced by the fermentation, and the temperature may have to be controlled within optimum limits. Air is excluded from the vats as much as possible to discourage the action of the vinegar- forming bacterium, and other harmful organisms.
Fermentation continues and is completed after several weeks.
The wine is racked off to separate it from the lees, or sediment of yeast, acid potassium, and other substances. In the case of quality wines, racking may be repeated at intervals for several years during the aging period in wood. During aging, and subsequent maturation in bottles, many reactions including oxidation occur, which enhance the taste, aroma, and preservative properties of the wine. During storage, wine requires protection from temperature extremes, from light, and from vibration. Bottles containing table wine are laid on their sides during storage to keep their corks moist.