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Co2 and ester's

Having done some experiments with different Belgian yeast. I have noticed that the less head space in carboy seems to produce more ester’s in my Belgian beers. I figure this is due to less CO2 building up and allowing the esters to produce more pronounced ester’s. The same beer the same yeast split into to different carboys . One 5 gallon and one 5.5 gallon… The 5 gallon had more ester’s than the 5.5 gallon. So I kept experimenting and used another Belgian yeast. Split batches and again the one with less head space in the carboy had more pronounced ester’s. Has anyone else noticed a difference less head space , less CO2 build up the better the ester’s are produced.

I have never experienced this, nor have I ever heard of anyone else noting the correlation. That doesn’t necessarily mean it doesn’t exist, though. There have been studies done relating to fermenter geometry and esters, though, so this may fall into that realm.

How yeast are you pitching in each, I’m wondering if it has to do with pitch rate?

I pitched same amount of yeast in both beers. Everything is the same Og and pitch rate. Only difference is size of carboys and head space in the carboy’s. Even had the same results with the second beer I brewed. Using a different yeast than the first beer I brewed i pitched same amount yeast in different size carboy’s and the one with less head space had more pronounced ester’s. After doing some research I did find as Denny mentioned fermenter geometry. In the book brew like a monk. On page 188. Greg Casey at Coors says in simple terms when Co2 levels increase around the yeast in the fermenter, the level of ester production decrease…

Or you could be seeing the effects of a change in carboy geometry since you’ve changed the size.

Keep in mind, though, that all of those studies were done on the commercial scale, with huge fermenters. The results may not necessarily apply to homebrewing scale.

Keep in mind, though, that all of those studies were done on the commercial scale, with huge fermenters. The results may not necessarily apply to homebrewing scale.[/quote]. Wouldn’t geometry still apply even on a smaller scale? There is a noticeable difference in ester’s from one carboy and the other and only difference is the head space in the carboy.

I’ve heard of fermenting in a keg under pressure reducing esters and open fermentation increasing esters but because the air lock releases all pressure above a certain point I don’t think there would be a difference in CO2 levels. They would be slightly more CO2 in the one with more head space at one time but not at a higher pressure as long as the air lock were filled the same. But I maybe I’m thinking of it wrong. You have experienced it twice, but I just don’t see the logic of how its happening due to CO2. Are you controlling the fermentation temps in the same exact way?

I wouldn’t assume the results are applicable. While they might be, the study wasn’t done on carboys.

I wouldn’t assume the results are applicable. While they might be, the study wasn’t done on carboys.[/quote]
As scale changes, the average pressure on a working yeast cell changes. That seems to be one of the significant factors that all those studies on fermenter geometry have isolated. So beer will ferment differently in a 6 gallon carboy than it will in a 6000 gallon tank of the exact same proportions.

Not many studies have been done by professionals on small scale batches - no money in that. That’s why homebrewers can discover new dynamics that just plain don’t show up in commercial operations.

[quote=“rebuiltcellars”]As scale changes, the average pressure on a working yeast cell changes. That seems to be one of the significant factors that all those studies on fermenter geometry have isolated. So beer will ferment differently in a 6 gallon carboy than it will in a 6000 gallon tank of the exact same proportions.

Not many studies have been done by professionals on small scale batches - no money in that. That’s why homebrewers can discover new dynamics that just plain don’t show up in commercial operations.[/quote]

Scale is one reason that autolysis might be an issue for commercial brewers but isn’t for homebrewers, too. The lack of studies at the homebrew level is what lead Drew and me to write our book.

I’m writing ever thing down and going to continue to experiment. There is definitely something to this and is a noticeable difference in esters between carboys. I have assumed that it is the difference in head space and CO2 and still could be… I have checked my pitch rate per carboy and I’m not under pitching according to yeast calculator. So I think I can rule under pitch out and over pitch out.

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