Diacetyl Rest Timer

How It Works

Diacetyl is a natural byproduct of fermentation that tastes like butter or butterscotch. Yeast produces diacetyl precursors (alpha-acetolactate) early in fermentation, then reabsorbs and converts the diacetyl later. A diacetyl rest raises the temperature toward the end of fermentation to help yeast metabolize remaining diacetyl. This is critical for lagers (where low fermentation temperatures slow diacetyl cleanup) and optional for most ales (where warmer temperatures handle it naturally). Start the rest when fermentation is about 75% complete (roughly 2/3 of the expected gravity drop). Raise temperature gradually (2-3F per day) to avoid stressing the yeast.