Keeping a sourdough starter alive through a Japanese summer
A Japanese summer is not kind to sourdough starters. From late July through early September, kitchen temperatures in Kanazawa regularly reach 30 to 34 degrees Celsius, and humidity sits above 80 percent for weeks at a time. At those temperatures, a starter can go from peak activity to overfermented and acidic in a matter of hours. We have been managing our starter through ten summers now, and the approach has changed considerably since the first one.
The main problem: speed
In summer, a starter that normally peaks in 8 to 10 hours at room temperature will peak in 3 to 4 hours. If you are feeding once a day and leaving it on the counter, you will come back to a starter that has already peaked, collapsed, and is now sitting in a pool of hooch. The grey liquid that forms when the starter runs out of food. This is not fatal, but it is not ideal for baking.
The fix is straightforward: either feed more frequently, or move the starter to a cooler environment between feedings.
Refrigerator management in summer
During July and August, we keep our starter in the refrigerator between feedings and take it out for 2 to 3 hours to peak before using it in a dough. We feed it once a day regardless of whether we are baking, using a 1:5:5 ratio (one part starter, five parts flour, five parts water) to give it enough food to last through the cold period.
For home bakers who bake once or twice a week, a once-weekly feeding with a high ratio (1:10:10) is sufficient to keep the starter alive in the refrigerator over summer. Take it out the night before you plan to bake, feed it, let it peak at room temperature, and use it when it is at its highest point.
Signs your starter is struggling
If you are seeing these signs, the starter is not dead. It is stressed. Feed it twice a day for three to five days with fresh flour and water, keep it in a cooler spot, and it should recover. We went through exactly this in August 2019 after a refrigerator failure and had the starter back to full strength within two weeks.
- Very sharp, vinegary smell rather than the usual mild yogurt sourness
- Liquid separating on top within a few hours of feeding
- Dough that spreads rather than holds its shape after bulk fermentation
- Loaves with very dense crumb and little oven spring
Summer is genuinely the hardest season for sourdough in Japan. If yours is struggling, it is almost certainly recoverable with consistent feeding and a cooler environment.