I often make fermented beet kvass. This was going well in summer, but now in the colder weather the environment is too cold for the kvass to ferment properly. The home temperature is 60F, but the kvass needs 72F-75F.

What is the best way to keep the kvass jar warm? A heating pad with a thermostat?

  • This question would probably be a good fit for the Homebrew Stack Exchange site.
    – user5561
    Commented Jan 14, 2014 at 1:42

2 Answers 2


If you are handy with electrics and electronics, linking a heating element to a PID controller is probably your best bet for stability.

This will give you quite stable temperatures.

You can find many sets of instructions by googling homemade sous vide pid,which is a very similar application, although higher temperature ranges are usually the goal.

  • This would certainly work, but is overkill. A lot of brewers use aquarium heaters or "brew belts", and if they work for beer, they'll work equally well for kvass.
    – user5561
    Commented Jan 14, 2014 at 1:46

While the sous vide method will give you a very easy to use environment for great results with minimal effort, it requires expensive equipment. I have invested 70 Euro worth of materials, many hours pushing bits in ugly C code, and one 220-volts accident, and mine is not ready yet :( Commercial ones are much more expensive, and frequently out of stock.

But people have been making fermented beverages in cold climates long before the first PID controller was built.

It is usually sufficient to heat the kvass in jars to a temperature which won't kill the bacteria in it, then pack it in some isolation. My grandma uses an old wool coat for her yogurt, but a container, possibly a beer cooler full of warm water, will give you a more stable environment. This will keep the liquid warm for many hours, until the fermentation is done.

Be aware that you will have to experiment a lot with the start temperature and the insulation to get the process to work well. If the temperature is lost too soon, the fermentation won't complete. If you start from too high a temperature, it will keep warm for longer, but you will get a rapid fermentation, which produces a very sharp tasting product. If you don't want the taste to be too strong, use thicker isolation and a lower starting temperature.

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