Yeast count is a neccessary and sufficient condition to prevent stuck fermentation.

I have done a bit of reading on this site and off and wonder about the oxygen needs of high gravity beers. In the small quantities I typically deal with (5 gallons) I wonder if dissolved oxygen beyond atmospheric conditions is necessary for fermentation. From what I can tell, initial oxygen is mainly necessary for yeast cell mitosis. Once the population is built up, oxygen is detrimental to the beer.

I have had a few stuck fermentations, and I think my problem is insufficient yeast count. With temperature control (mash and ferment), and sufficient initial aeration (though vigorous shaking) the only variable to cause a stuck ferment is yeast count.

Does anyone have anecdotal or scientific evidence to dispute this scenario:
Boil a high gravity wort, shake the crap out of it, pitch the proper amount of yeast from the calculator, maintain temperature control during the ferment = no stuck fermentation?

P.S. Don't get me wrong. I see the convenience of an O2 system. I just am not sure its necessary even in a high gravity beer.

I think there are more variables at play that can create a stuck/slow/incomplete fermentation. O2 certainly helps. Is a "system" necessary? Probably not. While I don't think it, in itself, is the solution to all fermentation issues, stuck or otherwise, it does eliminate the question, "Does the yeast have proper oxygenation to reproduce and metabolize sugars?"

If you pitch enough yeast, especially if it was well oxygenated in the starter, you can ferment a high gravity beer fully with no worry of a stuck fermentation.

However, if you over-pitch to compensate for under-oxygenation, that may lead to other problems. For example, many beer styles have a characteristic flavour derived from the yeast, such as Belgian beers. Much of that yeast character originates during the growth phase of the yeast life cycle. If you are short on oxygen, you won't get sufficient growth, and that character won't be produced.

That is probably the biggest concern, but I have also heard people suggest that over-pitching to compensate for under-oxygenation can also increase the risk of off-flavours from yeast autolysis, as well as increase your risk of production of unwanted compounds in your beer, particularly higher alcohols likel fusels (especially if you ferment on the warm side).

A final thing to consider is that fermentations from over-pitching are somewhat less predictable/less consistent than those at optimal pitching rates. So if you are trying to brew very consistently from batch to batch (e.g., experimenting with a recipe, or trying to perfect a recipe, or competition brewing), you may have a tough time.

Once the population is built up, oxygen is detrimental to the beer.

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Is this even an issue? I thought the yeast used up most if not all of the O2 and the CO2 scrubs the rest out. One of the reasons I really try hard to get quick starts is to get the CO2 going so it scrubs out any remaining, unused O2 and doesn't give any gremlins much of a chance.

I've also read that O2 is important for the cell wall...which probably is related to FlyGuy's comment about autolysis. I wash my yeast so I'm thinking I'd like a good, strong cell wall (just intuitively). I used to use a SS stone and an aquarium pump but now I just use a wire whisk because I think it works better. But I'm told a small bottle of O2 is like $10 from Home Depot and I still have the SS stone so I'm gonna give it a try, hopefully tomorrow. I don't have any experience with really high gravity brews.

SpanishCastleAle said:

Is this even an issue? I thought the yeast used up most if not all of the O2 and the CO2 scrubs the rest out. One of the reasons I really try hard to get quick starts is to get the CO2 going so it scrubs out any remaining, unused O2 and doesn't give any gremlins much of a chance.

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Its not really an issue. As you say, the yeast uses it up. It is possible to have too much dissolved oxygen in the wort but I don't recall why. I mainly brought it up because mead and some wine can be stirred during the fermentation to release the C02 and infuse oxygen.

SpanishCastleAle said:

I've also read that O2 is important for the cell wall...which probably is related to FlyGuy's comment about autolysis. I wash my yeast so I'm thinking I'd like a good, strong cell wall (just intuitively). I used to use a SS stone and an aquarium pump but now I just use a wire whisk because I think it works better. But I'm told a small bottle of O2 is like $10 from Home Depot and I still have the SS stone so I'm gonna give it a try, hopefully tomorrow. I don't have any experience with really high gravity brews.

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What are you using for a regulator?

noisy123 said:

Its not really an issue. As you say, the yeast uses it up. It is possible to have too much dissolved oxygen in the wort but I don't recall why.

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Oxygen is toxic to yeast at high enough levels. But unless you're oversaturating with pure O2 for a long time, this won't be an issue. I regularly dose O2 for 60 seconds or so and haven't had any problems.