A couple of months ago I double dropped a batch of beer. I really was just moving a fermenting beer because I had brewed a couple of days before my fermenter was available and started fermentation in my kettle.
I was surprised that fermentation really sped up after the transfer and was very vigorous. That time I just poured between buckets like it was a bucket of water.
Since then, every batch I have waited 24-36 hours after pitching yeast and then opened the fermenter lid and stirred up the trub on the bottom of the fermenter and agitated the surface to aerate a bit.
Every batch I have done this with has sped up shortly after. I am regularly getting very vigorous fermentation and regularly getting to FG in about 4 days from pitch.
I have kegged many of these batches at the 7 day mark.
I’ve done this at least 7 batches; lagers and ales. I have done it with Diamond, 34/70, Bry-97, and Verdant IPA yeast. All of the beers have been great.
My beers usually clear after about a week in the keg (with my usual yeasts; S04, Bry-97, Diamond, S23, 33/70, Verdant). I don’t think clearing happens any sooner or later with this method.
I’ve done this a couple of times with fermentations that stalled — I don’t have enough samples to be statically significant, but it seems to help things get moving again.
Edit: I don’t know if it’s the agitation of the yeast or the degassing CO2 that helps … :shrug:
My hypothesis is that rousing the yeast that is alive but flocculated is what invigorates the fermentation. I also think there may be yeast cells that grow in the trub pile to eat sugar there, but then can’t get into suspension on its own. That yeast may get roused as well.
Rousing yeast by rocking a carboy gets the yeast back into the beery rather than settled out. If you have a conical you can apply CO2 pressure to the dump valve and blow the yeast out of the cone back into the beer. Vinnie Ciluzo talked about doing that sometimes. For the homebrew scale it only takes a couple PSI.
The CC classic Double Drop aerates the beer and be give the yeast O2 if they need it. Some English strains have a high O2 requirement. Mark van D used to talk about that. Pumping through a fishtail rouses and aerates.
Brewing big beers I will give the beer a shot of O2 as bout 16-18 hours in to help the yeast.
sacch (and others i beleive) always advocated a bernoulli tube to aerate on the homebrew scale. i need to get around to that still. but yes, i am still very much in favour, even of internet-opinion estimates of O2 requirements being attached to certain yeasts. it definitely varies greatly between yeasts.
