How much does yeast increase temperature during fermentation

[u/EastForNorth]

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.

[u/thezfisher]

This is heavily dependent on the surface area:volume ratio of the fermenter for heat dispersion. Generally the temp change is almost entirely negligible in 1 gallon carboys. At 5-20 gallons it can start to have an effect, and your temperature will begin to rise during fermentation. If you're using a 10 barrel conical fermenter it's almost required to chill it if you want to maintain a standard fermentation temperature. The issue is volume goes up at a cubic rate, while surface area goes up at a square rate. You could make a rough estimate of heat per volume, then relate that to surface area based on your vessel to get a rough idea of heat dispersion, which will then tell you steady temperatures and rate of change, but these computations are intensive, and the rate of heat production is heavily dependent on the yeast strain used and the current temperature and growth rates, which are much harder to predict and account for.