Fermentation Calculator

Fermentation time and temperature are the two most critical variables in any fermentation project. Temperature governs microbial activity rate — too cold and fermentation stalls; too hot and you kill your culture or produce off-flavors.

General fermentation rate relationship: Q10 Rule: Rate doubles for every 10°C (18°F) temperature increase Estimated Days = Reference Days × Q10^((T_reference − T_actual) / 10)

This means fermentation that takes 7 days at 20°C takes approximately 3.5 days at 30°C — and 14 days at 10°C.

Reference points used by this calculator. Each row gives a temperature and the time you should expect at that temperature. The Q10 rule above then scales from there for whatever your kitchen is actually doing.

Sauerkraut and kimchi share a temperature but not a timeline, which surprises people who lump them together. Kimchi is usually eaten young and then moved to the fridge to carry on slowly; sauerkraut is normally left to go properly sour, and two weeks at room temperature is a fair starting point. Both are ready when they taste ready, so start sampling well before the number above.

Salt concentration for vegetable ferments: Salt % by weight = Salt / (Vegetables + Salt) × 100 Ideal range: 2–3% salt by weight, which inhibits harmful bacteria while still letting Lactobacillus thrive.

Worked example, sauerkraut: 1 kg cabbage | 20 g salt: Salt % = 20 / (1000 + 20) = 1.96% → slightly low; use 25 g for a safer 2.4%.

pH monitoring: Successful vegetable fermentation drops pH from about 6 to below 4.6 within the first 48 hours. Under that level, harmful bacteria cannot survive, which is the whole point of the salt.