While there are a myriad of faults that brewers discuss, debate, and diagnose, one of the most common is diacetyl, which is a fermentation by-product found in basically all fermenting (and some fermented) beers. Under normal circumstances, yeast cells are happy to go around and clean up the diacetyl produced while creating ethanol, but sometimes they don’t get to it all (usually through our own mistakes).
Today isn’t about how to avoid diacetyl, but here’s a quick and dirty primer:
1. Select a yeast strain that is less likely to produce diacetyl.
2. Hold the initial fermentation temperature in the lower range for the yeast.
3. Bring the fermentation temperature up a few degrees in the last few days of active fermentation and hold it there for 3–7 days.
4. There. Now you know how to avoid diacetyl (in theory).