Homemade Tempeh Incubator from an Old Mini-Fridge

I really like making tempeh at home, but I hate that it puts my oven out of commission for 1-2 days. I would place the tempeh in my oven with the light turned on to ferment it. That doesn't bother me too much in the summer, but I use my oven a lot during winter.

I wanted to make a stand-alone incubator. I've seen designs online for making one from a Styrofoam cooler, but I wanted something more sturdy. Luckily, Steve's parents had an old mini-fridge that they don't use anymore (and not even sure it worked) so they gave it to us. I don't care if the refrigeration part of it works; I just want it as an insulated box.

Here's the fridge.

I think it sat outside for a long time; it was very dirty. We cleaned it up. It doesn't have a shelf, but luckily a cooling tray of mine fits in it perfectly. Tempeh needs to incubate on a wire shelf so air can flow all around it.

This is the lighting we bought from Lowe's: Portfolio Candelabra Base Switch Cord. We also got a 40W incandescent light bulb for it. It must be incandescent - it needs to generate heat to get the fermentation started. The light fit snugly in the bar of the top shelf.

This is what the fridge looks like with the light. I have an oven thermometer, but the lowest it reads is 100°F. I need to keep it around 88°F for tempeh, so I put a candy thermometer in there to check it.

The wire for the light is fed in the seal of the door. So this can't create a perfect seal. I don't think this is too much of a problem. I can't dim the light, so the only ways to adjust the amount of heat in the incubator is to change lightbulbs (to a higher or lower wattage), turn the light on or off, or open the door slightly to let some of the heat out. Just doing a quick test, trying to close the door as much as I can (with a 40W bulb) made the incubator a bit too hot for tempeh. I'd need to keep the door open a bit to have the right temperature anyway.

I'm hoping to be able to use this for more than tempeh. I'd like to try making soy milk yogurt in it, using the light to generate heat to culture the beneficial bacteria. I'd like to start eating more fermented and cultured foods, as I've read about all their health benefits. I hope to find more foods that I can make using this incubator.

I also hope to incubate cold process soap in there. That doesn't need a heat source, just an insulated box to go through the saponification process. I can take out the light for that to make the door seal properly. I don't expect to have any issues with that. I've used my oven and microwave (both turned off) to incubate soap before.

I'll make another post after I've tried all this to say how it went. Wish me luck!