When making a white wine, one passes the newly harvested grapes through a crusher and stemmer. This machine removes the grape stems and seeds and crushes the berries. The macerated product may then be chilled prior to fermentation. In some cases sulfur dioxide is added prior to crushing and stemming. Usually white wine grapes are pressed shortly after crushing and stemming, which means that the juice is separated from the skins and seeds. The resulting product is called must. Most often sulfur dioxide is added at this time in order to kill any naturally occurring yeasts in the grape juice. Now the must is allowed to settle up to 48 hours. At this point yeast is added and fermentation commences.
During the fermentation process temperatures are controlled. Fermentation is stopped when desired residual sugar levels are reached. The wine is then racked and ready for malolactic fermentation, which is a bacterial fermentation (anaerobic) without air exposure. Nutrients may also be added to aid bacteria in their growth and development.
Barrel ageing is next in the chain of events, although some white wines are fermented in the barrel. Following the barrel ageing the wine is filtered, fined and bottled.
Needless to say, the above information is greatly simplified as will be the following explanations of red wine and sparkling wine production. There are many different wine making techniques available to be used by practicing enologists.