I'm wondering if anyone knows, or has resources to information on regulating ferment temperatures without electricity.
Specifically I am currently trying to grow koji. Ideally I must maintain a temperature of 98F. I know I could put a pot of water on low heat with the ferment suspended inside, but am looking for an alternative. If anyone can help, thank you!
I've faced a similar conundrum trying to make tempeh on my formerly off-grid homestead. The idea that worked best was to put the pot of hot water inside of a cooler, with the tempeh on a rack above the pot. The degree to which the lid of the cooler was open regulated the temperature into the critical zone between 80-90 F for tempeh. It would start out wide open when the water in the pot was very hot, and then work it's way to completely closed. After the first twelve hours or so the tempeh would produce enough of it's own heat that keeping it under a towel would let it continue fermenting even with the cabin in the 60's.
I know it's an old thread, however, here's an excellent resource for making koji without electric aids. Between the book of miso and the instructions from GEM Cultures, there are lots of ideas on how to grow koji with or without fancy incubators.
For my koji making, I keep it in the oven, sometimes with the light on, but usually the koji makes enough of it's own heat once it gets going. For the start, I'll heat up something ceramic or cast iron to keep the temp in the oven warm. Something that holds its heat well.
edit to add: the temperature range for koji is actually very forgiving. I usually keep between 85 and 95F with a goal of 91, for most of the koji growing process. Remembering that in the past, koji spores were often grown without fancy gadgetry like thermometers. Of course, there are ideal temperatures depending on what you want the end result to be - miso, sake, amazuke, &c. and what grains you are using, and which koji spores you are using, and what stage of the process you're at, and...