A
stuck fermentation occurs in
brewing beer or
winemaking when the
yeast become dormant before the
fermentation has completed. Unlike an "arrested fermentation" where the winemaker intentionally stops fermentation (such as in the production of
fortified wines), a stuck fermentation is an unintentional and unwanted occurrence that can lead to the wine being spoiled by
bacteria and
oxidation. There are several potential causes of a stuck fermentation-the most common are excessive temperatures killing off the yeast or a
must deficient in the
nitrogen food source needed for the yeast to thrive. Once the fermentation is stuck, it is very difficult to restart due to a chemical compound released by dying yeast cells that inhibit the future growth of yeast cells in the batch. At the winery winemakers take several steps to limit the possibility of a stuck fermentation occurring, such as adding nitrogen to the must in the form
diammonium phosphate or using cultured yeast with a high temperature and alcohol tolerance. These steps that winemakers may take to prevent a stuck fermentation will each have their own subtle or dramatic effect on the resulting flavors and quality of the wine.