Fermentation Temperature Rate Calculator
Calculate how temperature changes affect fermentation speed using the Q10 rule.
Predict new fermentation time when raising or lowering your fermentation temp.
Fermentation is a chemical process driven by enzymes — and enzyme reaction rates roughly double for every 10C rise in temperature. This relationship is captured by the Q10 coefficient:
rate_new = rate_base x Q10^((T_new - T_base) / 10)
For most fermentation: Q10 = 2 (doubles every 10C) For sourdough: Q10 is closer to 2-3 (bulk fermentation is particularly temperature-sensitive) For lactic acid fermentation: Q10 ≈ 2
Practical meaning
If a beer ferments in 7 days at 18C and you raise the temperature to 22C, the rate increases by a factor of 2^(4/10) = 1.32. The beer finishes in about 7 / 1.32 = 5.3 days.
If you drop fermentation temperature from 22C to 10C (to cold-crash or do a slow lager fermentation), the rate drops by 2^(-12/10) = 0.43. A beer that finished in 5 days at 22C would take about 5 / 0.43 = 11.6 days at 10C.
Upper and lower limits
This rule applies within the yeast or bacteria’s active temperature range. Most ale yeasts stop working above 30-35C and go dormant below 10-12C. Lager yeasts function at 8-14C. Sourdough starters stay active down to 4-5C in the fridge but become very slow.
Off-flavor risk. Fermenting too warm does more than just speed things up — it stresses yeast and produces more fusel alcohols and esters. For beer, stay within the yeast manufacturer’s recommended range even if the math says you could go faster.