Should I pitch a second round of yeast?

Question

I brewed a Dogfish Punkn clone that was rather heavy on the sediment. I pitched a pretty healthy yeast starter that was working for 30 hours before being pitched probably around 80 degrees, perhaps slightly more than the room temp. The yeast didn't take off, airlock activity was brief and underwhelming. It began at the 48 hour mark and lasted until the 60 hour mark. The krausen rimming the carboy is short, perhaps less than an inch. Should I pitch a new batch of yeast? It has been fermenting for one full week. I wasn't able to take a gravity reading because I busted my hydrometer. Any thoughts would be greatly appreciated.

Answer 1

You're going to have to take a gravity reading in order to determine whether or not fermentation has completed. It clearly did ferment given your description of events, but now it becomes a question of how much, and whether or not it has completed.

I suspect you may have under-pitched despite using a yeast starter, which would cause an extended fermentation past what normal ale fermentations take. Under the right circumstances, most ale fermentations develop a krausen well before 24 hours and should complete in about a week, assuming normal fermentation temperatures, average gravity, proper yeast pitch rates, and average yeast attenuation. Altering any of the above variables can dramatically alter the time needed to ferment to completion with varied consequences, either good or bad. For example, I recently brewed a Belgian Tripel using a new Belgian yeast strain boasting an unbelievably high 85% - 100% apparent attenuation. In the second week of fermenting, it dropped a further 5 gravity points. A lesser attenuating ale strain would have completed fermentation in a substantially shorter period.

Unfortunately, pitching more yeast may have likely been the solution back in the beginning a week ago, but will not benefit you at this point in the fermentation, unless you have a stuck fermentation, in which case you'll want to follow steps to correct the stuck fermentation. Any consequences of under-pitching yeast will have already developed by now. Best to wait it out, take gravity readings to see if it has completed, correct if stuck, and eventually go to bottle/keg.

For future reference, use Mr. Malty's yeast pitching rate calculator to determine the correct size for your yeast starters, it should hopefully prevent this in your upcoming batches.