FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
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Contents:
Wort chiller design... (Aaron Gallaway)
Re: CO2 (steve alexander)
Re: CO2 (Joe Walts)
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Date: Sun, 8 Mar 2009 22:36:13 -0700
From: Aaron Gallaway <baseball_junkie at hotmail.com>
Subject: Wort chiller design...
To one, to All...
I am at the tail end of rebuilding my brewery(finally got the
engineer on my Tug weld my stand for me) and am planning a new
chiller...would like some input from those with a PVC CF design.
Planning 50' of 3/8" ID copper coiled to 5" coils fitted into a 2'
section of 6" PVC with end caps and 5/8" hose barbs for cold water in
and outs with a capped 4" length of PVC fixed in the middle of the
coils to force the water to flow across the coils rather than pass
through the center decreasing the heat exchange values. Any thoughts,
ideas, suggestions and pictures would be greatly appreciated.
Thanks,
Aaron the Tugboater
PS, my tug engineer turned fledgling home brewer seeks a quality honey
brown recipe...anybody have one??
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Date: Mon, 09 Mar 2009 07:05:14 -0400
From: steve alexander <steve-alexander at roadrunner.com>
Subject: Re: CO2
AJ, as usual, produces a clear concise descriptive example; this time
of CO2 at brewery scale.
One aspect of carbonation and decarbonation that receives little
attention is the rate at which equilibrium is approached. We all know
that in addition to CO2 pressure we must apply agitation and/or, or in
introduce CO2 via a stone to approach equilibrium rapidly ... but
that's not quantitative. Then the opposite problem occurs when you
open a bottle the rate at which it decarbonates varies wildly from a
minor fizz to a gusher that will almost match a "mentos gusher". So
what exactly is going on here ?
I'm sure there is a diffusion eqn for the CO2 in solution/gas phase
and the rate is probably related to surface areas and
concentrations(pressures). That one I'm sure I can lookup and
recognize. The decarbonation seems to often be more closely related
to nucleation sites. It's easy to imagine that any beer, even the
filtered stuff has enough particulate that shaking can cause an
"upset". OTOH when we take pure seltzer water and shake it .... what
happens ? Apparently the (at equilibrium) CO2 bubbles mixed into the
water are sufficient to cause nucleation. That last one is a bit
strange, but I'm not a physical chemist. I think there should be an
entropy increase and a temperature decrease as beer decarbonates, so
with enough carbonation perhaps we could dispense with fridges and
chillers (joke).
I think there are some pieces that perhaps AJ can explain wrt beer
carbonation/decarbonation process. The usual sources ignore the
transition and just suggest you add a certain amount of CO2 and dismiss
the details of how this addition takes place with a handwaving mention
of stones and pumps. Then there is an implicit assumption that CO2 is
released at the appropriate rate when the bottle cap is popped or the
beer is pushed past a tap. Obviously this is not always the case.
> The obvious message here is that 6 kg of CO2 which do not end up in
> the beer, are nevertheless paid for ($12) and (for those who worship
> at the church of Al Gore) released to the atmosphere.
In AJs example we are discussing 1000gal(3785L) of beer and quibbling
about 17 kg of CO2 retained and perhaps another 6kg lost for
carbonation. If this is a conventional strength and attenuation beer
then it starts with ~476kg of extract, perhaps ~300kg is fermentables
and fermentation release a bit under 150kg of CO2! IOW we only need
about 15% of the CO2 for carbonation. Even in a brewery where
fermentation CO2 is retained for use in carbonation there is a very
large CO2 release. Twice as much CO2 is released as the beer drinker
exhales, so this 1000gal of beer results in ~450kg of CO2
release. This might anger the AlGorites, except we can associate this
CO2 release with the magical words (for those who with magical
thinking processes) "renewable", or "recyclable" or "green" or some
other claptrap. The carbon ultimately came from the atmosphere as the
barley grew in fields and this makes it acceptable to some sects of
AlGorism. Somehow the fact that petrol and coal carbon also originated
in the atmosphere, tho' less recently, doesn't create any acceptance
by that cult. BTW I'd like to introduce anyone who uses the phrase
"renewable energy" to the first & second laws of thermodynamics -
muddled thinking reflected in muddled terminology.
Anyone interested in the energy problem should examine this free book,
downloadable book from U.Cambridge Press.
http://www.inference.phy.cam.ac.uk/sustainable/book/tex/sewtha.pdf
The author, a Cambridge Physicist examines the energy issues in a
highly readable and informative way. He dispels a lot of popular and
political lunacy wrt grain ethanol, photovoltaics and the realistic role
of wind, tidal and nuclear in any realistic future. His primary example
is the highly populous UK, with a rather different resource mix, tho'
he examines other places and the general issue in detail.
His graphs of the EU carbon trade value shows a disastrous trend
that we US'ers should examine closely given the new carbon
cap&trade plans that Geithner estimates will cost over
$800Bn.
-S
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Date: Mon, 9 Mar 2009 10:25:46 -0500
From: Joe Walts <jwalts at gmail.com>
Subject: Re: CO2
A.J. - I checked my calculations against yours and they all agree. I
wasn't talking about atmospheric CO2 breakout. What I was trying to
say is if you have a half-full keg of beer in equilibrium, the mass of
CO2 in the beer is greater than the mass of CO2 in the headspace. At
least, that's what the calculations claim. Are you saying that's true
based on the reduction of gas pressure in solution? If so, it's
pretty counter-intuitive (to me) and I'm glad that you can explain it.
I changed the formulas in my spreadsheet to compute the headspace CO2
mass with the Redlich-Kwong equation instead of the Ideal Gas Law.
Both methods gave similar answers and suggest that, at serving
temperatures, the beer in a half-full keg holds a larger mass of CO2
than the headspace.
Back to the original question. Joe K - are you referring to the
common commercial brewing practice of adding CO2 through a carbonation
stone (at around 30 psig) while slowly bleeding CO2 from the headspace
to avoid overpressurizing the tank? It's wasteful of CO2, but it uses
less energy than a pump and it's fast. I don't think there's any way
to calculate the volume ahead of time unless you know the mass
flowrate out of your bleed/relief valve. The basic procedure is to
add CO2 for a set amount of time, check the beer's carbonation level
with a Zahm & Nagel CO2 tester and repeat. With practice, you'll
develop a sense of how much time it'll take to reach a desired
carbonation level on your system.
Joe
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End of HOMEBREW Digest #5522, 03/09/09
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