I have only been making tempeh for a short time. I keep reading about ideal temps for the fermentation process and have no problems getting my tempeh to the temps of 91 degrees F. Where I struggle is maintaining the temps over time. I insert the temp probe from thermometer used for monitoring aquariums in the center of my tempeh batch when I first put it into my incubator. I use my Instant Pot Ultra 6 quart model and set it for Low Yogurt which maintains at 91 degrees F.
After 18 hours the temps in the tempeh shows 95 degrees F so I take my tempeh containers out of the incubator and put them on a wire rack on my kitchen counter. The containers are 3 cup Sterilite plastic containers with holes punched in the bottom, sides, and lid. I fill the containers about one inch deep. I made one batch where the tempeh never went over 99 degrees F after 14 hours outside the incubator but most times the temps can climb as high as 122 degrees F.
What I had started doing is setting a temp alarm so that when the tempeh temp goes over 110 I move the container to the bottom shelf of my fridge till the temp drops to 90 degrees and then I move it back to my counter. I'd rather not have to do this but I haven't come up with any other way to keep the temps below 110 degrees.
I'd like to hear if others monitor their temps during this process and what they do to moderate the temperature during the fermentation process.