Wine Country History and Information

Fermentation of Grapes into Wine

Fermentation is the process whereby yeast converts natural sugars in the wine grapes into alcohol. In the traditional French style of wine making, naturally occurring yeast on the wine grape skins are used in fermentation. In the California Wine Country, winemakers typically add certain types of cultured yeast, which bring control and consistency to the fermentation process.

In the case of red wines, the “must” (juice and skins) is allowed to ferment in large stainless steel tanks for up to 14 days at a temperature of 70 - 88 degrees Fahrenheit. It is crucial for red wines to ferment along with the skins in order to attain their red color and much of their complex rich flavor.

Because of the tendency of the skins to float to the top of the tanks, the mixture must be “punched downâ€? throughout the process and juice “pumped overâ€? or circulated from the bottom back over the top of the tank. Once fermentation is complete, the juice and skins may remain in contact for another few days or even weeks in order to extract even more color and flavor, a process known as “maceration.”

White wine, which does not need to extract any additional color, will first be pressed, the skins removed and only the juice will ferment for 1 week to 2 months at a temperature of 42-65 degrees Fahrenheit.

After the primary fermentation process is complete, some wines, chiefly reds as well as some whites, will go through a secondary or ‘malolactic’ fermentation. Malolactic fermentation occurs when certain bacteria are added to the wine to induce the conversion of malic acid (which has a tart, bitter quality) into lactic acid (which has a much rounder, softer taste). 

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