Even if we don’t have a stuck fermentation, would rousing the yeast be a good thing? Other than keeping the yeast in suspension, would there be a benefit from driving off CO2 or sulfur components?
Also, even if there’s still an active fermentation – meaning there are frequent bubbles in the air-lock – do we even need to worry about oxidation?
Rousing yeast is a great technique for keeping active yeast suspended in the wort as you are nearing the end of the fermentation of really big beers. And No, as long as you are producing CO2 you shouldn’t have to worry about oxidation.
But why bother rousing yeast if the fermentation is chugging along, unless you’ve selected
a strain that’s unattentuative and a great flocculater?
Usually there’s enough yeast in suspension to keep things going to finish.
That was part of one of my questions. Is rousing yeast beneficial in other ways, i.e. does it help release CO2 and H2S from solution? One would seem beneficial for yeast health, the other for your beer’s final flavor profile.
[quote]Airing Out the Difficulties
One by-product of yeast is hydrogen sulfide (H2S). Hydrogen sulfide produces a strong rotten-egg smell and is sometimes noticed at the beginning of fermentation. It can be carried over into the finished beer if not allowed to vent from the fermenter. The CO2 produced during fermentation will scrub hydrogen sulfide from the wort, and open fermentation or the use of an airlocked carboy will allow its escape.
[/quote]
I heard that this was something utilized often in wine-making, and it seems to carry over into brewing. It really depends, I guess, just how much remains in solution even with the airlock, but rousing should definitely help remove some of those volatile compounds.
I usually rouse the yeast on bigger beers near the end of the fermentation to keep it moving until the very last fermentable sugar baby is swallowed up and converted into goodness… 8)
I rouse the yeast at least once a day throughout the primary ferment…the biggest benefit of doing so is probably not realized until near the end of the primary period, but doing do from the start certainly doesn’t hurt.
I do similar to the professor . . maybe not everyday, but often enough throughout the primary. I liken it to what happens when you make a starter with a stir plate . . . A better population of healthy yeast is the result. How could that be a detriment? ???
I wish someone would explain how a stir plate adds oxygen. I’ve heard this for years, but never could figure out how it’s possible. If you mean making the already dissolved oxygen easier for the yeast to get at hence greater reproduction, yeah . . OK. But adding O2 as if pulling it into the flask from the outside world?? ??? Not convinced!
It’s because the yeast scavenge O2 that’s dissolved in the wort. Leaving the flask open to the air keeps O2 going into solution to replace what they’re using. So they effectively have an unlimited supply of oxygen.
