Definition - What does Secondary Fermentation mean?
Secondary fermentation is a stage of fermentation in the winemaking process. Usually lasting up to 2 weeks, the winemaker can choose whether the fermentation is completed in barrels, oak or bottles, depending on the style of wine to be made. The secondary fermentation stage ushers in the Malolactic fermentation stage, which transforms the harsh qualities in the wine into softer, more flavorful qualities.
WineFrog explains Secondary Fermentation
During secondary fermentation, the wines are racked to keep the dead and dying yeast cells out of the wine. 30% of the alcohol produced in a wine is made during secondary fermentation. This stage in the fermentation process is anaerobic, which means that the amount of air exposed to the wine must be kept to a minimum. Winemakers attach an air-lock to the fermentation vessel, which prevents additional air from being added to the mixture. It is this reduction in air that encourages the yeast to focus solely on making alcohol, rather than multiplying.
A common mistake is to believe that secondary fermentation is a second fermentation. This is not the case. During secondary fermentation, the rest of the living yeast originally added is consumed. Second fermentation occurs when new yeast is added to the wine to cause a second reaction (a common process for making sparkling wines).