Winemaking requires a series of steps. Decisions made by the winemaker during each step influence the final character of the wine. A winemaker must first decide which grapes to use and when to harvest them. After the grapes are crushed, the juice is converted into wine through a process called fermentation. Wine is then aged until it is ready for drinking. Grape growers harvest their crop as soon as the grapes have ripened, usually in late summer to early fall, with the exception of late harvest wine grapes, which are used to produce dessert wines. Winemakers commonly measure ripeness by the amount of sugar in the grapes. They may also consider the grapes' acid content, flavor, and aroma. Workers usually pick the grapes by hand. The grapes then go to the winery for processing. The grape harvest is sometimes called the vintage. In some years, a favorable climate produces grapes of especially high quality. Those vintage years are considered to be superior.

At the winery, a machine called a crusher breaks the grape berries and removes them from their stems. The crushed grapes and their juice are called must. The length of contact between the juice and the skin influences the color of the red wine, and the taste of all wine.

To make white wine, winemakers separate the skins and pulp from the juice. The juice them enters a tank or barrel for fermentation. In making red wine, the seeds and skins go into the fermentation tank with the juices. Stirring the mixture from time to time ensures that the color is extracted from the skins.

Fermentation is the chemical change in which yeast converts the sugar in grapes into alcohol. Some yeast grows naturally on the skins of the grapes. Some European winemakers allow this yeast to conduct this fermentation. In the United States and most other countries, winemakers add selected yeasts to the must to begin fermentation. During the fermentation, the yeast grows and changes sugars called glucose and fructose into the ethanol, a type of alcohol, and carbon dioxide gas. The carbon dioxide is released as bubbles. The yeast also produces various by-products that may add to the wine's flavor and aroma.

Fermentation also releases heat. Most wineries refrigerate the must to keep its' temperature constant during fermentation. Winemakers usually ferment juice for white wine at about 59° Fahrenheit and red wine juice at about 86° Fahrenheit. The temperature of the must influences the rate of fermentation, the retaining of grape aromas, 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. The fermentation of red wine takes from 4-6 days and 12-18 days for white wine.

Most red table wines and some white table wines undergo a second fermentation, by bacteria. This fermentation, called the malolactic fermentation, lowers a wine's acid content by converting a substance called malac acid into lactic acid.

A new wine appears cloudy after fermentation. Winemakers clarify (clear) by removing particles of yeast and other unwanted substances. Such particles may be filtered out, allowed to settle naturally, or separated from the wine by a machine called a centrifuge. Wine may be further clarified, or fined, by adding certain solutions that reduce the content of unstable or unpleasant components.

After clarification, wine goes into wooden barrels or stainless steel tanks for aging. Wooden barrels contribute their own flavor to the wine. The size of the barrel, the age of wood, the storage temperature and humidity, and the length of storage time all influence the extent of the aging process. Many wineries hold wine at a temperature close to freezing for one or more days so that a salt called potassium bitartrate will precipitate (separate) out of the wine. This prevents the salt from forming crystals in the wine after bottling.

Although some wines are soon ready for drinking, others must age a few years to soften harsh flavors and allow desirable flavors to develop. Wine is bottled after some aging, and it continues to age slowly in the bottle. 

Fortified wines, such as port and sherry, are made by adding brandy to fermenting must. The wine that results generally is sweet. Drier fortified wines are achieved by adding brandy near or at the end of fermenting. Sparkling wines are usually made by a second fermentation of the table wine. This fermentation may take four to eight weeks. The bubbles of carbon dioxide produced by the fermentation are trapped in the wine.