[guvna]

If anyone's unfamiliar with the concept, here's a nice piece on it: http://www.brews-bros.com/index.php/topic/921-rousing-yeast-aka-swirling/

My questions:

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?

[bonjour]

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.

Fred

[tony]

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.

[bonjour]

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.

When you are brewing really big beers, they all are

Fred

[guvna]

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.

[guvna]

I just found this little ditty: http://www.byo.com/stories/techniques/article/indices/8-aging/116-aging-gracefully

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.

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.

[bonjour]

CO₂ is a detriment to fermentation and it is toxic to yeast, so yes, getting excess CO₂ out the fermenting wort is a good thing.

[bluesman]

CO₂ is a detriment to fermentation and it is toxic to yeast, so yes, getting excess CO₂ out the fermenting wort is a good thing.

+1

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....

[homebrewdad]

Wouldn't it be easier to rouse yeast just by screaming, "Hello, Yeast!"?

[The Professor]

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. 

[denny]

Wouldn't it be easier to rouse yeast just by screaming, "Hello, Yeast!"?

That would be my preferred method!

[bonjour]

Wouldn't it be easier to rouse yeast just by screaming, "Hello, Yeast!"?

That method rarely worked with my kids

[dhacker]

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? 

Plus, it's good exercise!   

[ndcube]

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? 

Plus, it's good exercise!   

Isn't the purpose of the stire plate to make more oxygen available to the yeast?  Just curious because I don't use one at the moment.

[babalu87]

Wouldn't it be easier to rouse yeast just by screaming, "Hello, Yeast!"?

That method rarely worked with my kids

My kids listen better when I whisper 

[whispermode] hey, yeast you gots more sugars to eat according to the fast-ferment test data..[/whispermode]