Fermentation Head Space

[maltseeker]

Was listening to an archive of Beer Strong and mention was made that the pressure differences caused by different amounts of headspace in the primary fermenter could effect the flavor profile. Does anyone have any further details around this? How much would it take to cause a difference? I'm thinking about doing a split batch with different yeasts and would end up with only 3 gal of wort in a fermentation bucket. That's a 40% reduction in wort so a significant increase in headspace. The wort should be protected as there will be plenty of CO2 during primary fermentation but what about the pressure difference? Is it really going to make an impact?

[brewinhard]

My guess is you would probably see more of a difference in a filled carboy vs. an open bucket style fermentation. Ester production and fusel alcohol levels can vary from fermentation vessel to vessel (carboy, bucket, conical,etc) based on their geometry and headspace availability. Not really sure how much of a role headspace plays in our small homebrew scale, but would be worth doing a little experiment with.

[spiderwrangler]

but what about the pressure difference? Is it really going to make an impact?

Keep in mind that in this case it isn't the headspace that may cause a slight difference in pressure, but the depth (weight) of your liquid. This is why commercial guys are so adamant about getting beer off the yeast quickly, but it is rarely the same issue for homebrewers. IF you are brewing in a 30bbl cylindroconical, the pressure on the yeast at the bottom of the cone gets pretty high. Think about swimming 3 feet under the water of your pool (carboy) vs. diving all the way to the bottom (commercial conical).

[Kbar]

So, my question is; what are the pressure limitations of yeast cells? (1psi=2.31ftH2O)?

[spiderwrangler]

IIRC, there was an article by Whitey that gave numbers between 30-35 psi as the lethal pressures for yeast. If you were talking water density, you'd be looking at ~35 feet deep to generate lethal pressures. Beer is going to be somewhat denser, and though it will be much denser early in fermentation, the yeast will be carried up into suspension by the rising CO2, mitigating the pressure any one yeast cell is exposed to for extended periods. After fermentation stops, the yeast will settle, and be subjected to bottom of the tank pressures for extended periods. I'd expect most commercial tanks therefore would be less than 30 ft tall, but haven't been in any breweries big enough to know how large they get....