Beer Forum

I made an interesting observation on my latest brew.
I use a 6 gallon better bottle carboy that stayed in the same spot in my crawlspace during fermentation.
This was a PacMan recipe and easily, the most vigorous ferment I've had (I had a blow of tube that was blasting water around).

Anyway..I have one of those cheapo stick on temperature stickers on the carboy. At the height of fermentation, it read 69 degrees.
Fermentation is now done and it has sat quiet for a day or so. Temp sticker now reads 64 (ambient air temp is 62 in there, has been the whole time).

Could those little yeasties really add 5 degrees to 5.5 gallons of mass?

My last brew was a Tripel with WLP 530 Abbey Ale yeast. My 10 gallon batch in a B3 Conical rose from 65 f to 72 in less than 2 days. It was in a freezer with the door open and ambient temp was 62. It was a vig-or-ous fermentation with crazy blow off action.

yes they can!
best to choose a few strains to work with and memorize how they work with various worts

According to HBSY heat evolution during fermentation is about 3.6 kJ/l/hr (lots of assumptions here about strength of wort, speed of fermentation etc so consider this a nominal value.). As the specific heat of water is about 4.2 kJ/kg this implies that the temperature of a ferment from which no heat can escape there would rise 1 °C each hour and 10 minutes or so. In a large fermentation vessel, where the ratio of surface area to volume is small, this heat can build up and attemperation in some form is usually required. For a smaller volume, such as a carboy, the surface area to volume ratio is much larger and heat may escape nearly as fast as it is formed and you won't have as much of a rise but it depends on many factors (air currents around the fermenter, wort currents within the fermmenter, ambient air temperature, rate of fermentation...).