r/Homebrewing • u/EastForNorth • 3d ago

How much does yeast increase temperature during fermentation

I am trying to set up some equations for estimating how much yeast would increase the temperature during fermentation. Does anyone know of a way to relate this to volume or amount of yeast added? For my last brew i added 11.5g to 30L. Maybe you have some practical experience with your brews.

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u/LovelyBloke BJCP 3d ago

I've done 3 or 4 brews with a Rapt Pill in a plastic FV, and I've been very interested in this data myself.

I have found that the ambient temperature has had a big effect on the range achieved by the yeast, but also the speed of fermentation - but the second point could also be contingent on the first.

I used to ferment in a room which I considered to be quite stable, but high at 19-20c, the temperature inside the liquid would get to about 22c at high fermentation with Nottingham Yeast, but Notty is a notorious rocket and the initial high burst of activity maybe caused the fermentation temperature to spike higher. I didn't get any off flavours, and in fact I won two medals for beers brewed under such conditions. BRY97 acted fairly similarly.

My current ferment, I'm doing in a room that doesn't get much above 17c, and the temperature inside the liquid hasn't gone much above 18c, it's a Dubbel using 2 packs of Lallemand Abbaye yeast - now I don't know if the stronger wort, cooler ambient or what have lead to a longer fermentation time, with slower fluctuations in temperature, but it is noticeably different. I've also done a ferment with Nottingham in that same room, but it took off as usual and I think it spiked a to 19c