Can a Beer Ferment Too Quickly?

Question

My beer seems to be fermenting more quickly than predicted by the kit. The last beer I made was ready (with the correct final gravity) in just under a week rather than the 2 weeks predicted by the kit. The beer I have fermenting right now seems like it will be finished fermenting in the next few days (the bubbles are coming very slowly) and it's only been in the carboy for about 5 days. The kit predicted 2-3 weeks.

The last beer was an amber ale and this one is a chocolate stout. The carboy is being kept in a closet at about 68 degrees.

If I reach my final gravity does it matter how quickly the beer ferments? Should I be worried about this?

Answer 1

There's finished, and then there's finished. Even after the yeast has stopped producing alcohol and carbon dioxide in quantity, it's still working. Most importantly, it's busy removing acetaldehyde and other nasties from your beer. From a taste perspective, beer that's drunk too early tastes "green" because the yeast has not had a chance to do its cleanup.

For a normal (i.e. not far from 1.050) gravity beer, three weeks is probably enough time. Leave it for another couple of weeks, and then take gravity readings on two consecutive days to be sure it's finished fermenting. Then bottle. As Denny said in a comment on a similar, post, let the beer dictate the schedule.

To answer your question, yes a beer can ferment too quickly. High temperatures during make for quick fermentation, but the yeast will produce more off flavours and hangover compounds. 68 F. is on the high side of acceptable, to my mind. Considering that the fermenting wort will be 3 or 4 degrees above ambient, you might try to keep ambient temperature in the low 60's to produce cleaner beer.