Some ferments like Yogurt, Koji, Natto and Tempeh require fermenting for extended periods of time at a temperatures between 88-110ºF, which is warmer than most ambient room temperatures, but lower than a standard oven temperature. The following are some tips on how to hack the right temperature for your ferment!
Most ovens don’t have a low temperature setting of 100ºF, but some older gas ovens stay warm to the touch simply from the pilot light. Use an oven thermometer to test the resting temperature.
If your gas oven has an interior light bulb, try turning that on. The warmth from that light, plus the pilot light may warm your oven just enough! Turn your oven light on for at least 30 minutes and use an oven thermometer to test the resting temperature.
Use an insulated cooler with hot water bottles or an electric heating pad as an incubator to maintain the heat.
Convert the interior of a cupboard into a warm incubator with a low-level heat source, like a high-wattage light bulb.
Use a seedling heat mat as a heat source (which generally raises the temperature 10º above the ambient temperature). Depending on your ambient temperature combine this with an insulated cooler.
Use a large cube-shaped dehydrator with removable trays.
Use a bread proofer.
Use an Instant Pot.