Proper temperature is vital for successful tempeh fermentation. Tempeh is ideally fermented within a temperature range of 85° to 91ºF. Regardless of the method used to keep the tempeh warm, it is important to verify that proper temperature can be maintained during the process. Here are a few methods for maintaining the proper temperature:
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Large cube-shaped dehydrator.
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Use a bread proofer with temperature controls.
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Oven with a low temperature setting or with just the light turned on. (Check the temperature of the oven first as ovens vary in heat.)
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Cupboard with a low-level heat source (like a high-wattage light bulb).
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Styrofoam or plastic cooler with warm water bottles or hand warmers to maintain the heat.
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Low-temperature mat such as those sold for reptiles (pet store) or to maintain sprout seedlings (gardening store). Please note, these mats generally keep cultures about 10 degrees above the ambient temperature. Set the tempeh on the mat and cover with a towel for insulation. This is not the same as a commercial heating pad which normally runs far too warm for this purpose.
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Incubate outside in a warm climate.
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A warm part of a home during the summer months (e.g., a non-climate controlled attic, etc.).
After the first 12 hours, the tempeh begins to generate its own heat. Remove from the heat source and wrap in a towel or place in an unheated cooler if the ambient temperature is below 75°F. If the ambient temperature is above 75°F, the tempeh will not need any additional insulation and will continue to culture.
