Factors affecting fermentation

The time required for complete fermentation of white grape juice or crushed red grapes varies greatly. The temperature maintained in the fermenting mass is the principal factor affecting duration of fermentation (as well as resultant character of the wine), more even than the initial sugar concentration (see must weight), yeast type, the aeration of the must, and the quantity of micronutrients in the juice, especially nitrogen. In general, red wine fermentations are complete within four to seven days but white wines, which are frequently fermented at much lower temperatures, may sometimes require longer, possibly two to three weeks, occasionally months (see dried-grape wines, for instance).