Why doesn’t beer freeze in an outdoor fermenting tank like in a can?

When I talked to Bell’s Brewery Founder Larry Bell a couple of weeks ago about pulling distribution from the Commonwealth of Virginia, I asked him how business was going.

“Well, it’s a tougher playing field out there these days,” said Bell. “We were able to achieve growth last year, and so far [2019] has started out good. January would have looked better if we didn’t have all the bad weather we had up here. We couldn’t get trucks out.”

It’s been cold here in the Midwest the past couple of months (we’re in Cleveland), and while that has messed with beer shipments, it has given Bell’s Director of Operations John Mallett the opportunity to drop a little science. People keep asking Mallett and friends: Why doesn’t beer freeze in those big fermenting tanks that sit outside? Because of the yeast party, explains Mallett. In Bell’s fermenters, there is generally a collection of some 5.6 quadrillion yeast eating sugar and producing alcohol, and that process generates heat — about a million BTUs of energy in Bell’s tanks. That yeast party and a nice thick jacket keep fermenting beer in its liquid form.