Fermentation Heater

Fermentation temperature control can mean a world of difference in the quality of beer. One of my early hurdles in homebrewing was keeping my carboy cool enough through the warmer months. Too hot of a fermentation can encourage the production of fusel alcohols and esters leading to off flavors and aromas. This can be solved with water/ice baths, wet towels, and more advanced means.

Too cold of a fermentation is another problem altogether. Get your yeast too cold, and they may fall asleep before they get the chance to do their job. For some, this means not brewing in the coldest months.

When my daughter was much younger, I often found myself immersed in playtime with several of her favorite toys. I recall setting up my daughter’s Easy Bake Oven in my garage one day shortly after Christmas. The weather was cold and I was inspired. I mean, if a light bulb can bake a cookie, how well would one warm up my beer in the winter months?

Of course, there was the obvious hurdle of exposing a fermenter to so much direct light. Having always been taught that light can skunk a beer, I knew it was going to be a little more involved than sticking a light bulb next to my fermenter (for more on that, this column from Mr. Wizard).

Enter: The paint can heater. The plan was to enclose a lightbulb in a case that would radiate the heat generated from the bulb into the surrounding area, therefore raising the temperature of the fermenter, without exposing the fermenting beer to the light source.

My first results with a 60-watt incandescent bulb heated the paint can enough to raise the temperature in my chest freezer from 58 °F (14 °C) to 68 °F (20 °C) in just a couple of hours. Once there, the temperature held steady with my temperature controller.

A word of caution, a 60-watt incandescent bulb can get that paint can heater quite hot. I’ve since replaced that bulb with a 40-watt bulb, which still does the job. Even with the lower wattage, I don’t recommend using this next to or inside of objects that might easily catch fire. Avoid using in wood fermentation chambers, closets with clothes, or towels, cloth, etc. nearby.

For this build you will need a temperature controller unit that allows for heating. Beyond that, the build itself is quite inexpensive, costing about $12. I only made one of these, as it has worked for so long I haven’t needed to change it. If I were to build it again, as you may, I might do a few things to clean up the build a little bit, such as attach the pancake box a bit differently to avoid the screws sticking through the top. I could have also gotten away without using the spade terminals, but felt they were a nice touch. Those details may be determined by how picky and knowledgeable you are regarding DIYs, but even if you go with the basic design, I have to say it works great.

With summer upon us, now is the perfect time to build this project so it’s ready to keep your fermentations warm when the weather gets cool.


Parts List

Ceramic keyless lamp holder
6-foot (1.8 m) power cord (rated to 221 °F/105 °C or higher with ground recommended)
Strain relief/grommet
Metal round pancake box
Spade terminals (optional)
Aluminum paint bucket
Light bulb (incandescent or indoor flood, 40W max, 25W preferred)