During which part of brewing is diacetyl most likely to be produced?

Diacetyl is most likely to be produced during the fermentation stage. This compound is a byproduct of yeast metabolism, particularly when yeast is actively fermenting sugars into alcohol and carbon dioxide. High levels of diacetyl can occur if the yeast is under stress or if fermentation happens at inappropriate temperatures.

During fermentation, yeast can produce diacetyl from the degradation of certain amino acids. It is essential for brewers to monitor and manage fermentation conditions to minimize diacetyl production. Notably, yeast can usually reabsorb and process diacetyl into less volatile compounds before bottling, provided that there is sufficient time and the fermentation conditions are optimal.

In contrast, other stages of brewing, such as boiling, cooling, and bottling, typically focus on different processes, such as sterilization and carbonation, where diacetyl is neither produced nor present in significant amounts.