Incubation temperature

Indonesian tempeh shops don't use incubators but let their tempeh ferment for about 2 days at room temperature, which is around 25°C. In colder climates it is important to incubate tempeh in a special place where temperature can be maintained at optimal level. But what is this optimal temperature? The Book of Tempeh mentions a temperature of 30-31°C for incubating tempeh at home or in a community.

Optimal growth temperature

We determined the optimal growth temperature of our Rhizopus strain by measuring the growth rate at different temperatures and arrived at below graph. This growth rate is defined by the relative size of one colony after 20 hours of growth on potato dextrose agar.

As you can see from this graph, the optimal growth temperature is 34°C, but growth rate is still high in the range 30-37°C. Below a temperature of 22°C or above 41°C the Rhizopus molds show practically no growth.

Optimal incubation temperature

Does this mean that we have to set our incubator in this 30-37°C temperature range? Unfortunately it is not that simple. During tempeh fermentation the metabolism of Rhizopus creates a lot of heat. For example, when the incubator temperature is set at 30°C the inside of the tempeh can easily reach a temperature of up to 38°C. This temperature rise starts after 10 to 12 hours of incubation, when you can see the first visual signs of fermentation. We recommend setting the incubator temperature initially at 32-34°C and reducing it to 28-30°C after 12 hours. Alternatively, you can set the temperature at 30°C during the whole incubation process, but then the total incubation time will be a few hours longer.