Biga in the fridge or at 18°C?
How temperature changes biga fermentation, how fridge hours compare to hours at 18°C, and how to adjust the yeast.
Most biga recipes give two options: around 18 hours at 18°C, or a couple of days in the fridge. Both work. The difference is how fast the yeast works.
Temperature sets the pace
Yeast activity roughly doubles for every 10°C in the range we use for dough. So, compared with 18°C:
| Temperature | Yeast activity | 1 hour counts as |
|---|---|---|
| 4°C (fridge) | about 0.4× | about 23 minutes at 18°C |
| 18°C (wine fridge) | 1× | 1 hour |
| 22°C (cool room) | about 1.3× | about 1 h 20 min at 18°C |
| 28°C (warm kitchen) | about 2× | 2 hours |
The calculator uses this to convert any schedule into “hours at 18°C” and sizes the yeast from that.
How fridge hours compare
Gabriel Reboul’s biga recipe gives 18 hours at 18°C, or 36 to 60 hours in the fridge, with the same yeast. With the rule above, 47 hours at 4°C is about the same as 18 hours at 18°C, right in the middle of his range.
| Same yeast, same result | At 18°C | In the fridge (4°C) |
|---|---|---|
| Short | 16 h | about 42 h |
| Reference | 24 h | about 63 h |
Which to choose
At 18°C is the reference. It’s predictable and gives a well-developed biga in a day. You need somewhere that holds 18°C: a wine fridge is perfect. A room that swings between 16°C and 26°C will give very different results from day to day.
In the fridge is more forgiving on timing and fits a weekly routine: mix on Thursday evening, use on Saturday. Things to know:
- Fridges vary. Many run between 3°C and 7°C, and the door is warmer. A fridge thermometer helps.
- Cooling takes time. A large container of biga takes hours to cool down, so it ferments faster than the fridge temperature suggests at first. The calculator doesn’t model this, so a fridge biga may be ready a little early.
- Wetter bigas belong in the cold. A biga at 60% hydration ferments faster than one at 50%. Gabriel keeps his 60% biga at 2–3°C for 24–48 hours.
Adjusting the yeast
Keep the yeast proportional to the time at a given temperature: half the time, double the yeast. The calculator does this for you. Enter the biga time and temperature, and it gives the yeast.
If you’d rather keep a fixed yeast amount, set the yeast amount to “Set manually”. The calculator then estimates how long the biga needs at your temperature.