Which aroma is commonly associated with excessive diacetyl levels?

The aroma commonly associated with excessive diacetyl levels is buttery and slick. Diacetyl is a compound that can form during the fermentation process, particularly when yeast is under stress or when there is insufficient yeast health or management. It contributes a distinctive buttery flavor and aroma that can be reminiscent of popcorn butter or butterscotch.

When present in moderate levels, diacetyl can sometimes add complexity to certain beer styles, but excessive levels can be considered a flaw. In many classic beer styles, especially lagers, the presence of diacetyl in high concentrations is often deemed undesirable. Therefore, recognizing the buttery aroma as an indicator of excessive diacetyl is crucial for quality control in brewing.

Other aromas listed like floral and citrus, nuts and caramel, and burnt and roasted suggest other compounds or processes, which do not typically relate to the specific profile created by diacetyl.