It’s Time to Buy a Reptile Heating Pad

The microorganisms that perform the transformative magic of fermentation are very sensitive to temperature. In general, the warmer it is (within a range they can survive) the faster they reproduce and metabolize. 

But faster is not necessarily better: Slow fermentations tend to produce more complex flavor than quick ones. And small differences can be surprisingly profound, as I learned when comparing yogurt fermented at 105°F and at 110°F: The texture, the tang, and the butteriness of the final product all shifted.

Being able to control the temperature gives you more control over how your fermented food comes out. And if you love a batch you made and want to repeat the same results, temperature control makes that easier.

The Chamber

The first thing you need is the chamber itself—a place to keep your fermenting edibles where they won’t be disturbed. 

• A plastic and foam cooler works very well, because its insulated walls help keep the temperature steady. 
• A big lidded container, such as those made by Cambro or Rubbermaid, also works, especially if you wrap it with an insulating layer.
• A mini-fridge makes a very nice, very well-insulated compartment. 
• A kitchen cabinet will even work, which is what I’ve done at home.

Note that if you repurpose a container into a fermentation chamber, the process is completely reversible, so it’s not a permanent commitment. If you like, after a wash, the container can return to work transporting beer to the beach, or whatever its initial job was.

The Heat

Having selected an insulated container, it’s time to give it some warmth to contain. The temperatures we’re looking for in fermentation aren’t particularly extreme, so a gentle heat source works well. Back to the reptile heating pad!

For $10 or $20, you can get one that’s exactly the right size for your chosen chamber. It provides consistent heat, standardizing your results. They even make them for plants if you need a bigger one.

But, don’t get one that has its own temperature control built in: That’s the next step.

The Controller

The brains of the operation (present company excepted) is a thermostat: a device that includes a temperature sensor and a power controller. Simple models are available for under $40—Inkbird is a reliable manufacturer—and they work in a straightforward manner. 

Each one has an electric outlet and a probe on a wire. The heater plugs into the outlet on the controller. The probe goes on the food. There’s a temperature setting on the device, where you can enter the desired temperature for the chamber.

When the temp probe falls below the target temperature, the controller supplies power to the power outlet, thus turning on the heater. When the temp probe rises above the target temperature, the controller switches off the power. 

It’s not as precise as finely tuned algorithmic controllers such as those built into sous vide circulators, but it works perfectly for our purposes.

To assemble your fermentation chamber:

1. Place the heating pad in the bottom of the container. Optionally, a cooling rack on top of the pad will help distribute the heat more evenly.

2. Place the temperature controller next to the container, plug it into wall power, and plug the heating pad into the controller’s power socket. Connect the temperature probe to the controller.

3. Place your fermentable food in the chamber, and secure the business end of the temperature probe to the food. You can tape it to the lid of the jar, or otherwise place it in close proximity so that it reads the temperature of the food, not the distant reaches of the chamber.

4. Close the chamber (allowing the cords to pass under the lid or through the door). Set the controller to your desired target temperature, and be patient!

As you get deeper into the most delicious hobby, you can upgrade your chamber.

A tiny fan to circulate the air in the chamber provides more even heating, especially with larger chambers.

Inkbird makes a dual controller that has a humidity probe in addition to the temperature probe and a second power outlet to which you can attach a tiny humidifier (to keep the humidity in your chamber high, for activities like growing mushrooms) or a dehumidifier for lower-moisture applications like fermenting tea.

If you used that mini-fridge as your chamber, you can connect it to a dual temp controller, which allows both heating and cooling. The reptile heating pad switches on when you want to raise the temperature, and the fridge’s compressor kicks in when you want to lower the temperature, thus opening up the wide world of fermentation that happens below room temperature. Make your own kimchi fridge or wine fridge, or combine it with your dehumidifier and dry-age your own beef.