How to use the fermentation time adjuster
- Enter the time that worked in hours and minutes, and the temperature at which it worked.
- Enter the new temperature, and choose Fahrenheit or Celsius.
- Set the slowdown factor: how many times longer the rise takes for each 10 C (18 F) drop. The value in the box is an example.
- Read the new time. The check line moves it back to the first temperature and returns the time you started with.
Formula
new time = known time x slowdown^((old temperature - new temperature) / step)
step = 10 for Celsius, 18 for Fahrenheit
check: new time x slowdown^((new temperature - old temperature) / step) = known time
Each step of 10 C (18 F) cooler multiplies the time by the slowdown factor, and each step warmer divides it. Partial steps use the fractional exponent.
A cooler kitchen
A dough rose in 4 hours at 78 F. The kitchen is now 70 F, which is 8 F cooler. With a slowdown factor of 2, the exponent is 8 / 18 = 0.444 and the time is multiplied by 2^0.444 = 1.3607. The new estimate is 326.6 minutes, or 5 hours 27 minutes.
In Celsius, a rise of 90 minutes at 24 C in a room that is now 28 C is 4 C warmer, so the time is multiplied by 2^(-0.4) = 0.758, giving 68.2 minutes, about 1 hour 8 minutes. A 2 hour rise at 75 F moved to a 38 F fridge with a factor of 2.5 comes to 789 minutes, about 13 hours 9 minutes.
A model, not a law
Yeast and sourdough cultures speed up with warmth and slow down with cold, and doubling the time for every 10 degrees C of cooling is a rule of thumb many bakers use. The true curve changes with the culture and the dough, and cultures slow sharply near fridge temperatures. That is why the factor is yours to set. If your own results show 2.5 or 3, enter that.
Use it with your eyes
Dough volume, bubbles and feel are better guides than the clock, so treat the estimate as the time to start checking. For the dough temperature itself, see the Desired Dough Temperature Calculator. For ingredient ratios, use the Baker's Percentage Calculator, and for salt in vegetable ferments, the Fermentation Salt Calculator.
Assumptions and limits
- The slowdown factor is the same across the temperature range you use.
- Only temperature changes. The amount of yeast or starter and the flour stay the same.
- The factor must be above 1, so a cooler dough always takes longer.
- Food safety limits for long, cool or warm fermentation are not covered.
Frequently asked questions
What factor should I use?
The value in the box is an example. Try it, note how your own dough behaves in a cooler or warmer room, and adjust the factor until the estimates match your results.
Why are there different steps for Fahrenheit and Celsius?
The factor is defined per 10 degrees C. A 10 C change equals 18 F, so the page uses 18 when you choose Fahrenheit. Both give the same answer for the same real temperatures.
Does this work for vegetable ferments or yogurt?
The arithmetic applies to any process you describe by a slowdown factor, but the factor differs by culture. Use values from your own experience, and follow safe recipes for foods that ferment for days.
What does the check line show?
It takes the new time back to the original temperature using the same factor. If it matches your known time, the math is consistent, which confirms the exponent was applied in the right direction.