How is diacetyl chemically produced during fermentation?

Diacetyl is a compound produced during fermentation as a byproduct of yeast metabolism, particularly through the oxidative decarboxylation of acetohydroxy acids, specifically alpha-acetolactate. During fermentation, yeast metabolizes sugars and, in the process, produces acetohydroxy acids. These compounds can be further metabolized into diacetyl through a series of biochemical reactions that typically occur under certain conditions, such as oxygen availability and yeast strain characteristics.

The production of diacetyl is common in various styles of beer, with lager yeasts being particularly prone to producing it during fermentation. If yeasts are healthy and there is adequate yeast activity post-fermentation, diacetyl can be reabsorbed and converted back into neutral compounds. However, its presence can lead to off-flavors if not properly managed.

Understanding this biochemical pathway is crucial for brewing, as controlling diacetyl levels is linked to fermentation management, including the fermentation temperature and the yeast's health and viability. The other choices do not directly relate to the process of diacetyl formation during fermentation.