Definition - What does Primary Fermentation mean?
Primary fermentation is a stage of fermentation in the winemaking process. At the beginning of this stage, yeast - either naturally occurring or added by the winemaker - converts the sugars in the wine to alcohol. Usually lasting between five and 15 days, around 70% of the wines alcohol is converted during this process. Primary fermentation is followed by the longer, secondary fermentation.
WineFrog explains Primary Fermentation
During primary fermentation - and all of the stages of fermentation - the essential components in a wine combine to extract the color and tannin from the grape skin. As the yeast converts sugars to alcohol, the skins soak in the must. Chemical compounds are formed in the wines; these compounds are highly aromatic providing fruit, floral, vegetable and earthy smells.
Primary fermentation is also called aerobic fermentation; the container that the wine is fermented in has to be open to the air. Contact with air allows the yeast cells to multiply, something they do 100 to 200 times during the few days of primary fermentation. There is a lot of motion and foam on top of the must during this process.
There are several factors that winemakers must take into consideration. As the yeast converts sugars to alcohol, the temperature in the wine increases - winemakers must monitor that throughout primary fermentation to ensure the yeast doesn’t die from heat. Typically white wine is fermented between 18-20°C (64-68°F). A slightly higher temperature than that would bring out the complexity of the wine. Red wines are fermented at 29°C (85°F) with higher temperatures having a very adverse effect - killing the yeast and boiling off the flavors of the wines. Lower temperatures for red wines bring out the fruit flavors.