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Fermentation control for lager yeast

I’m planning to do some lager beers this winter using fermwrap (and Johnson temp controller) in my garage that is now about 55F, but will drop to about freezing as it gets colder here in Minnesota. My question is, has anyone used fermwrap in cold conditions to ferment at lager temperatures? I don’t know if it will keep the temperature at lager fermentation temps when the ambient temp is 32 or so. I plan to use a bubble wrap product I found to use as insulation over the fermwrap on my carboy.

Also, do you have to be concerned about the temperature going too high when you insulate the carboy well? That is, if you have a well insulated carboy in cold ambient temps, will the heat generated by fermentation of the lager yeast create fermentation temps above what is proper for lager yeast?

I realize that most people use refrigerators or freezers to create fermentation chambers, but I thought that I could create an inexpensive approach by just using my cold garage and a fermwrap.


I use a Cool Brewing Insulated Fermentation Bag

1 - 2L soda bottle full of ice lowers the temperature 5F. So if it’s 72F, you would use 4 bottles and swap out every 12 hours.

Probably cheaper than a temperature controller and fermwrap, though it’s not automatic and you do need to swap the bottles, but on the plus side again, you can simply ferment indoors year-round.

I don’t think a Fermwrap @ 40W IIRC would heat a carboy from 32 to 52 in a garage in the upper Midwest winters. If the carboy were in a freezer then it might have a fighting chance, but the winter environment of the garage is just too much for the fermwrap. It would be like trying to heat the garage with a 40W light bulb. (Fermwrap might be 25W, can’t remember for sure.)

Thanks for the lead on the fermentation bag, Manfred. I think that will be very helpful for brewing in the summer when my basement temps go above 70 and I need to reduce the fermentation temp.

After posting my question I found the manufacturer for ferm-wrap and a rep said it is rated @ 40W. He also said that it will handle anything for a 20 degree difference. Right now my garage is 48F and I’ve got bubble wrap insulation around the carboy and the temp is now at 76 (finishing off a Belgian ale), so it appears that the ferm-wrap may handle temp differences beyond 20F if the carboy is insulated well. This may be improved by putting the carboy in the fermentation bag, so it looks to me like I will likely be able to ferment at lager temps this winter, something I didn’t think I’d be able to do without a freezer or refrigerator. I’ll probably try a low temp lager yeast first, just in case I can’t get enough heat.


I haven’t used the fermwrap, but I do my lagers au-naturel in the Maine winter, which should be similar to Minnesota.
I have a basement that tends to stay in the low 60’s, but I can crack the door to my garage and let in a little colder air when needed. I can also move the bucket closer to the furnace and gain a couple degrees there for D-rest. Plus I constructed a Styrofoam lined box that I use with a heating pad if needed to get upper 60’s to 70’s. The garage tends to stay in the 40’s, getting down to low 30’s when it’s subfreezing out. I lager out there with carboys in swamp cooler buckets. Last winter I had some ice in the bucket, but the beer did not freeze.
The key is checking your temps a couple times daily and move the bucket to the appropriate site when needed.
I did 2 lagers two years ago, three last year and will do three in late November-December this year. Plus the Altbier currently in primary and a Doublealt to start next week which will go out to the garage for some lagering. Works for me! :cheers:

If you can build a simple box you can simply use a light along with your fermwrap to get the desired temps. Check this out: ... Can-Heater
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