What is a common sign of sluggish yeast during fermentation?

The presence of diacetyl is a common sign of sluggish yeast during fermentation. Diacetyl is a byproduct of yeast metabolism, particularly the result of yeast that is under stress or experiencing poor health. When yeast struggles to ferment sugars effectively, it may not convert diacetyl into more neutral compounds, leading to its accumulation in the beer. This gives the beer a buttery off-flavor, which is often described as undesirable.

In this context, high carbonation levels could indicate healthy fermentation and active yeast, while a clear beer appearance typically suggests that fermentation and subsequent clarification processes have gone well. Excessive hop aroma, while a positive attribute in some styles, is not related to yeast activity and would not be a sign of sluggish fermentation. Thus, the identification of diacetyl as an indicator of sluggish yeast effectively highlights the issue of fermentation health and yeast performance in producing a clean and well-attenuated beer.