ferment temp: ambient vs carboy

I just recently stuck a surface thermometer on a bucket after I had an Ale had almost a negative lag time. I have been keeping the carboys/buckets fermenting in the upstairs bathroom because basement is too cold right now. I have been making sure the room is about 68-70 and not worrying about it.

After this massive fermentation I had recently the bucket was really warm, and a surface thermometer was reading 78. Fermenting is an exothermic reaction, but what I am wondering is if the yeast temperature recommendations are based on keeping the temperature under control even during a very active primary fermentation? or is that the recommendation for ambient temperature of the room/closet/garage?

So, ultimately should I slow a active fermentation down to the recommended temperature by placing it in a cooler room until the fermentation slows down and yeasties quick creating extra heat.

-Jeremy

Temperature recommendations are for the temperature of the fermenting wort. This is the temperature that you're concerned about.

Yes, the fermentation temperature range is for the wort.

Ok, so my crazy active fermentation was fueled partially by an extra 8 to 10 degrees. I suppose I am going to have some off-flavors. I have been contemplating the fish tank heater in a bucket, to move the fermentation operation back to the basement. A good reason to actually do that.

How cold is your basement? A lot of ale yeasts will do great and ferment nice and clean in the low 60s, some down into the high 50's.

If it's in the low 50s, maybe consider doing some lagers.

where I live, currently the outside temperature is -6 C (approx.) 20 F....

since I don't have a heating at home while I'm at work temperature at home falls to 6 C (approx 42 F) while I'm away...


I have a beer fermenting in my living room with US-05 yeast.... this morning I only covered loosely the carboy with an ordinary blanket...


when I got home, I put the thermometer inside the blanket, on the surface of the carboy, and guess what - temperature inside this blanket was 20 C (66 F) while the temperature in the room was 6 C (42 F)!?

so the conclusion is that fermentation produces huge amounts of heat.... what's going inside the carboy should worry you

Yes, fermentation produces a significant amount of heat. A temperature rise of 8 degF on an uncooled carboy is believable - and it is also not good. Need to keep most ales around 70 or below to avoid esters and fusels. No need to dump the beer but it will likely taste like "homebrew". I now control fermentation temperatures by submerging my 6.5 gallon carboy in a temperature controlled water bath. I found that the heat transfer rate from my glass carboy into cool air was not high enough to maintain my fermentation temperature setpoint. The transfer rate is 10x higher when using water. Hope this is useful.