Fermentation Temperature Calculator

Fermentation Temperature is the single most important variable controlling the speed and flavor of fermentation. Too hot and you get off-flavors or kill the culture. Too cold and fermentation stalls.

How Temperature Affects Fermentation: Most fermentation organisms (yeast, bacteria) have an optimal temperature range. Within that range, activity for a yeast roughly doubles for every 10°C (18°F) increase, which biologists call a Q10 of 2. Turn that around and it means the time roughly halves for every 10°C you go up, and doubles for every 10°C you come down.

Two of the cultures here are not on 2, and this page uses their own figures rather than flattening everything to the same curve. A sourdough starter is 2.5, because it is a mixed culture of yeast and lactic bacteria and reacts harder to a cool kitchen than a straight yeasted dough. Sauerkraut and kimchi are 1.8, the flattest of the group. Those are the values on the Q10 fermentation rate calculator, which is where to go if you already know your own timing at one temperature and want it at another.

Be careful with the version of this rule you sometimes see quoted as “doubles every 10°F.” That would be a Q10 of about 3.5, which is far steeper than fermentation actually behaves, and it will have you badly underestimating a cool-room proof.

Optimal Temperature Ranges:

Timing Estimates: Fermentation time varies inversely with temperature within the viable range. Working from the Q10 rule above, every 10°F (5.5°C) below optimal makes the ferment take roughly 1.5x longer, and a full 10°C below doubles it.

Practical Example: Bread dough at 77°F (25°C) rises in about 1.5 hours. The same dough at 59°F (15°C) takes closer to 3 hours, but develops noticeably more flavor for the wait. Drop it to a 39°F (4°C) fridge and you are into overnight territory, which is exactly what retarding is for.

This page starts from the temperature and tells you whether it is right, with the timing as a by-product. The fermentation calculator starts from the same question and puts the time first.
Both run the Q10 rule off the same reference points and stop at the same temperatures, so a 30°C ale reads 5 days on either. Kombucha and tempeh are only here.

Cold Fermentation: Many bakers and brewers deliberately use cold temperatures (38–50°F / 3–10°C) to slow fermentation over 12–72 hours. This technique, called “retarding,” develops deeper flavors.

Tips:

• Use an instant-read thermometer to check dough and liquid temperatures.
• Ambient room temperature is not the same as dough/liquid temperature.
• A slightly warm oven (turned off, light on) creates a good proofing environment around 78–80°F (25–27°C).
• In cold kitchens, place ferments near a heat source or use a fermentation heating mat.