Raising fermentation temperature

Question

I recently upgraded my system to include temperature control, and I had fermenting a brown ale at 67 degrees for about 6 days. Took a gravity reading last night, and it was at 1.014 (down from 1.065/~78%AA). I'm not sure where I acquired this concept in my head, but thought I would raise the setpoint on my fermenter temp control to 70 degrees for 48-72 hours before racking. I'm not sure if the gravity will drop any further (or if I want it to, it tastes pretty solid right now), but thought it might help to let the yeast clean up diacetyl, acetaldehyde, or other nasties.

Does raising fermentation temperature have any positive or negative effects after flocculation?

Answer 1

You've basically got it right, you usually want to raise the temperature towards the end of fermentation so that the yeast stay active long enough to clean up diacetyl and acetaldehyde.

Typically you'll start raising the temperature after 48-72 hours of fermentation. You don't want to do it sooner, because the yeast will throw off more fusel alcohol due to the higher temps.

I raise the temperature by a degree or two per day, until I'm at about 72. Then I let it sit for 2-3 more days before racking off the yeast.

You don't always have to do this, some yeast will finish the job even without the temperature boost; but with highly flocculent or low-attenuating yeast, the technique is very helpful.