kombat
Well-Known Member
There are many topics that come up repeatedly in these forums. "Is this infected?" "Should I rack to secondary?" "It's been 2 hours and still no krausen - should I be worried?" But one in particular has me curious.
Whenever someone posts a thread about a beer that didn't attenuate as far as they think it should have, inevitably someone suggests swirling the yeast back up a little bit, or even pitching more yeast, as a way to prod the fermentation on a little bit further. But does this ever actually work? I don't recall anyone ever posting a thread along the lines of, "My gravity plateaued at 1.020, so I pitched another packet of rehydrated US-05 and got it down to 1.012." Intuitively, it doesn't seem like either agitation or repitching would do anything.
We all know there is more than enough yeast still in suspension to successfully bottle carb the beer (even after cold crashing), so why would those same, hungry yeast give up and drop out of primary fermentation if there were still fermentable sugars floating around? And similarly, if the yeast that have been in the beer all along and are acclimated to the environment have given up, why would a fresh pitch of yeast into such a hostile environment (oxygen and nutrient depleted, alcohol present, low pH) be able to find fermentable sugars that the hundreds of billions of yeast cells already there have passed over?
I guess I'm just skeptical that the advice actually accomplishes anything. I understand that raising the temperature can have an effect (as yeast will slow down and drop out if they get too cold), but I'm just not convinced that swirling the yeast will prod them to get back to work, or that pitching new ones will ferment anything the ones already there did not.
Is this outdated advice? Can we put it to bed? Or have people actually seen clear evidence that these practices have made a difference? That is, you had a beer that had definitely stalled out, as measured with a hydrometer over several days, and then after swirling or pitching more yeast, you saw the gravity resume dropping.
Whenever someone posts a thread about a beer that didn't attenuate as far as they think it should have, inevitably someone suggests swirling the yeast back up a little bit, or even pitching more yeast, as a way to prod the fermentation on a little bit further. But does this ever actually work? I don't recall anyone ever posting a thread along the lines of, "My gravity plateaued at 1.020, so I pitched another packet of rehydrated US-05 and got it down to 1.012." Intuitively, it doesn't seem like either agitation or repitching would do anything.
We all know there is more than enough yeast still in suspension to successfully bottle carb the beer (even after cold crashing), so why would those same, hungry yeast give up and drop out of primary fermentation if there were still fermentable sugars floating around? And similarly, if the yeast that have been in the beer all along and are acclimated to the environment have given up, why would a fresh pitch of yeast into such a hostile environment (oxygen and nutrient depleted, alcohol present, low pH) be able to find fermentable sugars that the hundreds of billions of yeast cells already there have passed over?
I guess I'm just skeptical that the advice actually accomplishes anything. I understand that raising the temperature can have an effect (as yeast will slow down and drop out if they get too cold), but I'm just not convinced that swirling the yeast will prod them to get back to work, or that pitching new ones will ferment anything the ones already there did not.
Is this outdated advice? Can we put it to bed? Or have people actually seen clear evidence that these practices have made a difference? That is, you had a beer that had definitely stalled out, as measured with a hydrometer over several days, and then after swirling or pitching more yeast, you saw the gravity resume dropping.
!!!!
