Cicerone Certified Beer Server Practice Test

What is diacetyl and how does it affect beer?

1. A compound that enhances beer flavor

2. A yeast strain used for fermentation

3. A byproduct of fermentation that can give beer a buttery flavor

4. A type of hop variety

The correct answer is: A byproduct of fermentation that can give beer a buttery flavor

Diacetyl is a byproduct of fermentation that is produced primarily by yeast during the metabolic process when they convert sugars into alcohol and carbon dioxide. The presence of diacetyl in beer can impart a distinctive buttery flavor, which is often considered undesirable in most beer styles, especially lagers and pale ales. The development of diacetyl is usually linked to the yeast's health and the conditions during fermentation. Proper fermentation management, including adequate yeast pitching rates and fermentation temperatures, can help minimize diacetyl production. Following fermentation, yeast may reabsorb diacetyl, further reducing its concentration in the finished beer, which is why conditioning periods are important. Understanding the nature of diacetyl is crucial for brewers and beer servers alike, as it directly affects the overall flavor profile and quality of the beer. While some styles may find a certain level of diacetyl acceptable, most strive to keep it as low as possible to maintain a clean and enjoyable taste.