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Lambic Digest #0406
From postmaster at longs.lance.colostate.edu Tue Jul 26 03:32:29 1994
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Subject: Lambic Digest #406 (July 26, 1994)
Date: Tue, 26 Jul 1994 00:30:08 -0600
Lambic Digest #406 Tue 26 July 1994
Forum on Lambic Beers (and other Belgian beer styles)
Mike Sharp, Digest Coordinator
Contents:
re: diffusion and gases (Jim Liddil)
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Date: Mon, 25 Jul 1994 9:18:16 -0700 (MST)
From: Jim Liddil <JLIDDIL at AZCC.Arizona.EDU>
Subject: re: diffusion and gases
Al worte:
%
% That's what you'd expect the Nalgene people to say. Ask the Corning people
% too. ;^).
Been there, did it. Glass is essentially zero. And Corning is not in the
bottle cap business. The reason media bottles (i.e wheaton) are shaped as such
is to minimize the head space when it is filled to to the 500 ml line. Corning
is in to glass making.
%
% Regarding your assertion that "no pH change = no diffusion," I'd like to
% investigate that. Mind you, my chem and physics are very rusty, so bear
% with me. What's the % CO2 in the atmosphere? A couple of percent?
a few percent? I hope not. CO2 is around 0.1 to 0.2%
%That is
% the % CO2 that the media in the container will try to reach to achieve
% equilibrium. I don't think that this concentration will cause much change
% in the pH.
Ding Dong you're wrong. The phenol read will show a pH cahnge with the lose of
CO2 from the media. Our media has excess bicarb to act as a buffer.
% O2 in the air is, what, about 18%... that's quite a
% bit more than CO2. Also, if I recall correctly, the rate of diffusion is
% proportional to the difference in concentration across the permiable membrane,
% so we would have a much faster rate of diffusion of O2 into our wort through
% a plastic fermenter than CO2 diffusion into your media, no?
oxygen and co2 are independent of each other. We worry about loss of co2 from
the media and oxygen getting in and oxidizing the components. Yes it is true
that everything in hte world wants to be a euqilibrium and fights to get there.
%
% Incidentally, PC is twice as permiable to O2 as HDPE and just a little less
% than twice as permiable to CO2.
But these numbers are still relatively small to the amount of diffusion that
occurs at the seal between a container and it's closure.
%
% I don't think the stopper itself allows much diffusion (even if it was very
% permiable, it's almost an inch thick!), but rather, as you said earlier, the
% space between the stopper and the glass or stopper and plastic is probably
% the questionable barrier.
The thickness is not that important. Most of matter is space. But yes the
seal is the problem.
Still, it's hard to imagine that 8 to 15 square
% feet of plastic are not going to allow significant O2 to permiate. As a
% datapoint, I brewed 15 gallons Ordinary Bitter in a 20 gallon HDPE container.
% I added my own gasket to the lid so I think that wasn't as bad a source of
% diffusion as it might have been.
I think the seal WAS the problem. Every HDPE container I have seen with a snap
on lid is far from perfect. Any gas is going to take the path of least
resistance. Bad is relative.
% Well, when the time came to bottle, I was
% busy and an extra three weeks went by with the batch sitting at 65F. It
% had the most intense acetaldehyde aroma and flavor (even more than Bud) and
% what with the rather mild flavor of an Ordinary, there was little to cover
% it up. I don't suspect it was the yeast's fault, it was Wyeast 1028 or
% 1056. In any event, I'm convinced of the high O2-permiability of these
% HDPE containers.
But is this this high permeability from the actual container or the seal? Try
the same experiment in a Nalgene HDPE carboy with a proper lid and see if you
get the same results. I think you are coming to conclusions which really have
no hard data to support them.
Jim
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