From the HBD Archive
Subject: Fermenting under Pressure
Date: 1992-05-01 16:18:31 GMT

> From: David William Bell <>
> I'm not an experienced enough brewer to do more than
> speculate, but:
> The idea of having all of the pressure build up in the
> fermentor because the CO2 may be a good thing leads me
> to ask:
> Wouldn't this break the yeast cell walls? I mean the
> argument for using a hydration step in water rather
> than in wort is because of cell damage. So, wouldn't
> the pressure be as bad for the yeasties as tossing
> them straight into wort for hydration purposes?

Here's an example of one other thing not to worry about.
Water (and presumably beer) is essentially an incompressible
fluid. That means that if you push on the top of it harder
basically nothing happens. If you don't believe me try
squeezing a completely full plastic soda bottle (no air in
the top now - that's cheating) and a completely empty
(except for air) soda bottle. The full one will deform but
not compress.

It's true that more CO_2 goes into solution under pressure
but that's because of the surface interaction. The gas
diffuses both ways across the surface but the bubbles
coming out of the beer say "Woha, too much pressure
out there. I'm going back into the beer to relax!"

The bottom line is that you shouldn't have to worry about
yeast cell walls. The purpose of hydrating is to reduce
osmotic pressure which is a completely different story.

If you really want to put your beer under CO_2 pressure
while fermenting (and I'm still unclear why) then you need
to use some sort of relief valve. A cheap one is to blow off
into a column of water. Unfortunately to get an extra 1.5 atm
of pressure you need a 50 foot column of water :-)

See Ya
Geoff Reeves
Atomic City Ales

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