Well it got down to -11°F/-24°C last week so I thought this would be a good time to discuss temperature control options for fermentation. There are a lot of options ranging from the simple to quite elaborate. I started out with my empty oven as an “insulated box”. The lowest temperature I could set it was 170°F/77°C which is too hot for most ferments so I would just leave the oven light on and it would maintain a temperature of about 110°F/43°C. Perfect for fermenting natto but really too warm for bread. I next tried a Styrofoam cooler with a ½ gallon bottle of hot water in it as a heat source. This was less than elegant. The jar took up too much space and temperature control was poor. I finally broke down and bought a PID temperature controller that allows me to pick a setting and have it maintained for days if needed. The PID is very versatile and I now use it with a home made sous vide system so it is in almost constant use.
The only thing left to do is choose the heat source, and with the PID controller the source must have a hard on/off to work as it controls the temperature by turning the source on and off. Seedling mats work well but a slow cooker will be needed for higher temperatures. I especially like the reptile mat I bought. It fits around a 5-gallon carboy or I can set it on its edge curled around several jars of fermenting kombucha to tide them through a cold spell. If cold temperatures are required for the ferment such as for lagers an old refrigerator or freezer can be used. In the summer heat ferments can progress too rapidly producing off flavors and undesired compounds. A PID controlled refrigerator is perfect for controlling this unless you are lucky enough to have a walk in.
I have also insulated my beer carboys with an old down jacket.
You can find information on the devices on the links page.