[pehlman]

What's the highest original gravity in which you can get likely get yeast to thrive and attenuate well? I have heard of people making very strong beers and having to start with a lower-gravity wort, and then adding small amounts of yeast and sugar as it ferments. Is there an upper limit as far as a how big of a beer one can make just using the usual method of pitching all the yeast at the beginning? Given proper yeast-count and aeration, of course.

[denny]

The ROT is about 12% ABV, but obviously there are a lot of variables.

[Joe Sr.]

I'm not sure the OG is the limiting factor, if that's what you're asking.

The highest OG wort I've made came in around 1.12 and was pitched on a yeast cake from a smaller beer, so all the yeast went in at the beginning.  This fermented down to around 1.045 or so, IIRC.

A different yeast may have taken it down further, but at some point the ABV becomes too much for the yeast.

I suppose you could start with whatever OG you want, but the higher you go on the OG the higher will be your final gravity.  How sweet a beverage are you looking for?

[tschmidlin]

What Denny said - there are a lot of variables.

Gravity is a big one, since this will cause osmotic stress.
Wort composition also affects osmotic stress.  Among other things, different sugars cause different pressures at the same concentration.
Yeast strain is another big one.
Temperature
Yeast health

Start with Denny's rule of thumb and go from there.

[pehlman]

I'm not sure the OG is the limiting factor, if that's what you're asking.

The highest OG wort I've made came in around 1.12 and was pitched on a yeast cake from a smaller beer, so all the yeast went in at the beginning.  This fermented down to around 1.045 or so, IIRC.

A different yeast may have taken it down further, but at some point the ABV becomes too much for the yeast.

I suppose you could start with whatever OG you want, but the higher you go on the OG the higher will be your final gravity.  How sweet a beverage are you looking for?

Thats what I meant...  I just didn't phrase the question very well... haha

I totally know that the gravity itself isnt the issue... I was concered with how far down you could get a given wort to ferment before needing to add more yeast and/or sugars.

Denny - Thanks! 12% is what I assumed it would be around. Ive never tried making anything above 11%

[nateo]

IIRC from "the literature" 1.120 is the threshold above which osmotic pressure becomes a real concern.

I think the term you're looking for is "vitality." Viability is a go/no-go thing, either the yeast is alive or dead. Vitality is more a measure of the health of the yeast. For example, you could have 100b "viable" cells that are sickly, and you could have 50b cells that are healthy. The 50b healthy cells will have better fermentation performance than the 100b sickly cells.

It's like sending one million grandmas into battle vs ten thousand young, healthy soldiers. Who do you think will win the day?

I've gotten S-04 up to 13% ABV, so the alcohol tolerance really depends on the vitality of the yeast, how you handle it, pitching rates, etc. But under the right conditions, you can get up into the 15-16% range like Avery does.

[morticaixavier]

It's like sending one million grandmas into battle vs ten thousand young, healthy soldiers. Who do you think will win the day?

Oh the grannies for sure. They know how to fight dirty. and what healthy young man would attack a granny?

[pehlman]

Nateo - yeah that answers my question thanks! Makes perfect sense. Love the analogy! Hahaha

[nateo]

If you have time to listen to the Shea Comfort interview on the brewing network, you should. A lot of brewers treat fermentation as a "set and forget" thing, where you pitch x amount of yeast, then you wait. To get the best fermentation in difficult environments, there are some techniques you can use to help your yeast out.

One thing that homebrewers don't do much of but pro brewers do a lot is rousing. Some rouse (with CO2) continuously until fermentation is done. Shea Comfort is a big wine-industry guy, but homebrews as well. He is a big advocate of constant rousing until you hit your target FG. It will ferment faster, and hotter, so temperature control becomes more important when going that route. But he's convinced it gives you better performance.

Shea rouses every batch he makes, but you'll really see the benefits on really big beers. With rousing and gradual feeding of sugar, you should be able to get away with just one initial yeast pitch on a really big beer.