Cold crash

Cold crashing is the practice of dropping a fermenter's temperature down close to freezing, often for one to three days, near the end of fermentation. The cold causes yeast cells and other suspended particles to clump together and settle faster than they would at normal fermentation temperature, which leaves the beer noticeably clearer before packaging.

This step is typically done after gravity has stabilized and fermentation is confirmed finished, using a fermentation chamber, a temperature controller paired with a refrigerator or freezer, or simply a cold garage in winter. Clearer beer straight out of the fermenter means less sediment carried into bottles or a keg, which many brewers prefer both for appearance and for a cleaner-tasting pour.

A common mistake is cold crashing before fermentation has truly finished, which can stall the yeast at a higher final gravity than intended, since cold temperatures slow yeast activity significantly. Another is racking too quickly right after a cold crash without letting the beer settle fully, or agitating the fermenter and stirring compacted sediment back into suspension right before transferring.