Sourdough Clock

Sourdough Fermentation Temperature: What 64–86 °F Does

By Tam Vu · Updated

On this page
  1. 1. Cooler is slower, a lot slower
  2. 2. Warmer is faster, but only up to about 81 °F
  3. 3. Warmer leans tangier
  4. Using this for your own bakes
  5. How the numbers were worked out
  6. Source

Temperature is the biggest everyday reason a sourdough schedule runs early or late. A 1998 study by Gänzle, Ehmann and Hammes measured how fast a sourdough yeast (Candida milleri) and a sourdough bacterium (Lactobacillus sanfranciscensis) grow at different temperatures. Their results explain three things bakers notice.

1. Cooler is slower, a lot slower

Using the study's growth model for the yeast, here is how long a step takes compared with the same step at 24 °C (about 75 °F). The model works in °C, so the rows are whole °C values with °F rounded:

Dough temperature Time compared with 24 °C (about 75 °F) A 5-hour bulk becomes
18 °C (about 64 °F) 2.26× 11.3 h
20 °C (68 °F) 1.63× 8.2 h
22 °C (about 72 °F) 1.24× 6.2 h
24 °C (about 75 °F) 1.00× 5.0 h
26 °C (about 79 °F) 0.88× 4.4 h
27 °C (about 81 °F) 0.86× 4.3 h
28 °C (about 82 °F) 0.88× 4.4 h
30 °C (86 °F) 1.07× 5.3 h

A drop from 75 °F to 68 °F stretches the same step by about 60%. That is why a recipe written in a warm kitchen can take most of a day in a cool one.

2. Warmer is faster, but only up to about 81 °F

In the study the yeast grew fastest at 27 °C (about 81 °F) and stopped growing at 36 °C (about 97 °F). Above 27 °C the model's yeast slows down again, which is why the table bottoms out at 81 °F and then climbs. Turning the heat up past that point does not speed the rise.

3. Warmer leans tangier

The bacterium in the study, the one that makes acid, grew fastest at 32 to 33 °C (about 90 °F) and stopped at 41 °C (about 106 °F). Below about 26 °C (79 °F) the yeast and the bacterium responded to temperature in a similar way. Above that, the bacterium keeps speeding up while the yeast levels off, so it gains ground relative to the yeast. The study notes that sourdough is usually fermented between 20 and 28 °C (68 to 82 °F).

Using this for your own bakes

The model gives relative speeds measured in lab cultures, not bread dough, and for specific strains. Your starter is a mix of its own. So:

  1. Time one bake at a known dough temperature: how long bulk took, and how long your starter took to peak.
  2. On another day, use the schedule calculator to scale those times to that day's temperature.
  3. Keep watching the dough. The model plans the day; the dough decides when a step is done.

The schedule calculator only works between 64 and 86 °F (18 to 30 °C). The study says its model is less accurate near the low end of the growth range, and the fridge is far outside it.

How the numbers were worked out

The study fitted each organism's relative growth rate γ to temperature T (°C) as γ = a × x^b × e^(−c × x) with x = Tmax − T. For the yeast, a = 0.029, b = 3.0, c = 0.34 and Tmax = 35.9 °C. The time factor between two temperatures is γ(reference) ÷ γ(new). For example, γ at 24 °C is 0.855 and at 20 °C is 0.523, so 0.855 ÷ 0.523 = 1.63.

Source