Once at the winery, a machine called a crusher breaks the grape berries and removes them from their stems.  Amazingly enough, this is a very gentle process and the stems that come out of the machine look as though each grape must have been removed by hand.  The machine then crushes the grapes, skins, pulp, juice, seeds and all and the result is called must.

The length of contact between the skin and the juice influences the color of red and blush wines and affects the taste of all wines.  To make white wine, winemakers separate the skins and pulp from the juice before it enters the tank or barrel for fermentation.  For red wine, the seeds and skins go into the fermentation tank with the juice.

Fermentation is the chemical change in which yeast converts the natural grape sugars into alcohol.  Some yeast grows naturally on the skins of grapes and many European wine makers allow this yeast to conduct the fermentation.  The winemakers in most other countries, including the United States,   add selected yeasts to the must to begin fermentation.  Carbon dioxide gas is a by-product of the fermentation process and is released as bubbles.  The yeast also produces various other by-products which may add to the flavor and aroma of the wine.

Fermentation also releases heat, so most wineries refrigerate the must to keep its temperature constant.  White wine is generally kept a good 20 degrees or so cooler than red wine.  Fermentation temperature affects the rate of fermentation, the aroma, and the formation of yeast by-products.  It also determines the rate at which the color and flavor of the grape skins transfer into the wine.  Red wine ferments in 4-6 days while white wine takes 12-18 days.

Many red wines, and some white will then undergo a second fermentation by bacteria called malolactic fermentation which lowers the acid content.

A new wine appears cloudy after fermentation and winemakers clarify the wine by removing particles of yeast and other unwanted substances either by filtration, allowing them to settle naturally, or separating them from the wine using a centrifuge.  The wine maker may further clarify the wine by the addition of certain solutions that reduce the content of unstable or unpleasant components.

Once the wine is fermented and clarified, it is time for the aging process to begin and the wine is transferred into wooden barrels or stainless steel tanks where it will remain until bottling.  The temperature and humidity conditions, the length of storage time and the size and age of the barrel all influence the aging process and thus the final character of the wine.

The wine is bottled after some aging, and will continue to age slowly in the bottle.  Most white wines are ready to drink soon after bottling, but many reds require an additional few years to soften the harsher flavors and allow desirable flavors to develop.  However, even red wines (unless you have some inside information about the bottle or the vintage) should generally not be aged beyond 10 years or so.  For while you may then end up with an extraordinary wine, you may also end up with an expensive bottle of vinegar.

Fortified wines, such as port or sherry, are made by adding brandy to the fermenting must, and generally results in a sweet wine.  Drier fortified wines add brandy near the end of the fermentation process.