Temperature is important for any ferment. Soy ferments are no different. Tempeh needs to be kept warm, but common fermenting appliances available in the US don’t work well. Yogurt makers are far too hot. A cube dehydrator or folding proofer work very well. However, beginners may not want to invest in a new piece of equipment.
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Seedling mats are inexpensive, with price tags anywhere from $15-$40, and are quite versatile. I purchased mine to give my water kefir, mesophilic yogurt and kombucha a heat boost in the winter. But I found it works perfectly for my tempeh!
Follow your recipe for tempeh, and spread the inoculated beans in a suitably sized baking pan. Cover with plastic wrap or a waxed cotton cover. If using plastic wrap, poke holes at regular intervals to prevent too much moisture from building up. Then set the pan on your seedling mat.
Above: Chickpea tempeh covered, monitored and ready to go. It is important to use a thermometer. When using a seedling mat, there is no lid to disturb or coolers to open, so checking the temperature is easy! If the ambient temperature is warmer, there is no need to cover the tempeh. Otherwise, use a towel to provide insulation. Plug in the mat and allow the tempeh to culture for 12 hours.
After 12 hours, vent the lid to allow more moisture to escape and remove the tempeh from the seedling mat. If the room is cool, keep the towel on the pan. If the room is warmer (above about 75°F, you may find that no towel is needed!
Above is a batch of tempeh on a very cold day. The stainless steel pan conducts more heat and the thick towel keeps it toasty. This option works best if your home is below 65°F. Monitor the temperature closely to avoid overheating your tempeh. This method does work especially well for making natto at normal room temperature too!
At 24 hours, I find my tempeh is matted well enough I can tip it out of the pan onto a plate or cutting board. I then re-cover the tempeh and let it culture another 12-24 hours.
After a total of 36-48 hours, the tempeh should be completely covered in fluffy, white, nutty smelling fluff. Wrap the tempeh and refrigerate, then enjoy it plain or in your favorite tempeh recipes!