Premature cessation of an alcoholic fermentation, commonly known as a stuck fermentation, is a serious winemaking problem. Restarting a stuck fermentation is often difficult and time consuming, but more importantly, it creates a favorable condition for the growth and activity of spoilage microorganisms. There are several factors that are responsible for fermentation problems.
Nitrogenous compounds play an important role in winemaking. They serve as nutrients for the growth and metabolic activity of the yeast during fermentation; and as proteins, they also influence wine stability, particularly in white wine.
Grape juice/must can be fermented by the yeasts present on grapes and in the winery. This kind of fermentation is often called natural or spontaneous fermentation. Some winemakers rely on spontaneous (uninoculated) fermentation to gain flavor complexity and, consequently, higher wine quality. In some cases high quality wines have been produced from uninoculated fermentations; however, the practice is not without risk.
Fermentation transforms the must into a young wine. Proper handling of young wines is very critical because mistakes made at this early stage can irreversibly damage the wine quality.