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HOMEBREW Digest #5330
HOMEBREW Digest #5330 Wed 07 May 2008
FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
Digest Janitor: pbabcock at hbd.org
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Contents:
RE: Braggots ("David Houseman")
Re: Peer review of Aeration Methods (Fred L Johnson)
Video from Big Brew Day ("Lemcke Keith")
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Date: Wed, 07 May 2008 07:37:05 -0400
From: "David Houseman" <david.houseman at verizon.net>
Subject: RE: Braggots
Dick,
Not to be pedantic but there are a number of reasons to boil wort for longer
than 30 minutes other than to extract bitterness from hops. Especially in
the production of Scotch ales where the extended boils (2 hours) create the
caramel and smokiness characteristic of Scotch ales. You might get away
using extract rather than all-grain and boiling a gallon of wort down to a
pint to create the caramelization. Suggest reading the style book on
Scotch Ale before you head off on this venture.
Dave Houseman
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Date: Wed, 7 May 2008 07:55:26 -0400
From: Fred L Johnson <FLJohnson52 at nc.rr.com>
Subject: Re: Peer review of Aeration Methods
Chan Lay posted a number of useful comments and questions to the
Aeration Methods paper, which I would like to address below. (Thanks,
Chan.)
>
>
> I'd be interested to know what your O2 level was (in ppm) for the
> rocking shaking method after 15min, as the general concensus is that
> 8ppm of dissolved oxygen is usually all one can expect to acheive from
> either shaking/rocking or from using an aquarium pump with an air
> stone.
Oxygen saturation levels on the days and at the temperatures and at
the location on which these experiments were performed ranged from
8.04 mg/L to 8.36 mg/L. You can simply multiply the % saturation
value by these numbers to get an idea of the absolute levels of
dissolved oxygen in the experiments. You will achieve different
absolute levels depending upon the atmospheric pressure and
temperature at which you perform the aeration.
>
> Just some critical review that may/may not help with future studies
> when expenses allow:
>
> 1. You've highlighted water was used instead of wort due to expense.
> Using wort instead of water would be the first thing i'd change. (As
> you already know, there are different O2 saturation levels between
> wort and water)
I agree that the better experiment would have been performed in wort,
but I seriously doubt any significantly different conclusions would
have been made. In fact the graph may not have changed at all except
for the % saturation value at the start. The absolute solubility of
oxygen in wort is, as stated, somewhat lower than in water and will
undoubtedly depend upon the solute content (gravity) of the wort, but
I doubt that the rate of dissolution is very different than for water.
>
> 2. Repeat the experiment at least 3 times (incorporate error bars
> to fig1)
I agree. The absence of a measure of repeatability is the greatest
weakness of the reported results. I was actually too lazy to repeat
these because I seriously doubt the conclusions would change and the
exact values are not important anyway (in my opinion).
>
> 3. Continue measuring the dissolved O2 level once you've ceased
> aeration to monitor if O2 levels continue to increase/decrease.
The dissolved oxygen content would undoubtedly continue to increase
until saturation is achieved, but the rate at which the oxygen
dissolves would be lower than the rate achieved by actively aerating.
>
> 4. As a -Ve control, measure the dissolved O2 level of a carboy
> fermenter filled with water/wort (filled from the bottom with out
> splashing). This can be your baseline. Be interesting to see if there
> is a increase in O2 level from just the surface contact with air.
The experiment using the bucket was performed with minimal splashing,
just as you suggested. DO was measured immediately after the 5
gallons had been transferred to the bucket, so there was not a
significant amount of additional time for oxygen to dissolve into the
water after the transfer was completed until it was measured. I doubt
using a carboy would make a significant difference. The bucket
experiment does illustrate that a significant amount of oxygen is
dissolved in the water by even a gentle transfer. As I said, there
may be sources of oxygen entering the water other than when it leaves
the tubing and enters the fermentor.
>
> 5. As a +Ve control, measure the dissolved O2 level of a full carboy
> that has been excessively oxygenated with pure O2 via airstone. This
> can be your saturation point.
The purpose of the experiment was not to re-determine the solubility
of oxygen in water/wort, and the values in the experiment were
expressed with regard to the well known published values of oxygen
solubility in water. Using pure oxygen would undoubtedly dissolve
more oxygen in the water or wort, as I acknowledged in the paper, and
future experiments to determine the absolute levels of oxygen in
water/wort versus time would be useful, as they could provide
guidance to the homebrewer of how long he should pump oxygen into his
wort to achieve the level desired. I think the bigger and more
difficult question to answer is, "What is the desired level?"
>
> 6. Do a yeast count and pitch homebrew levels of yeast (eg 1 mil
> cells/ML/plato) and then measure the opitcal density (600nm), to
> determine the affect each aeration method has on yeast division.
Such experiments are actually pretty well published. Providing a
continuous supply of air to the yeast allows for essentially maximum
growth, but it has undesirable affects on flavor. Hence, methods of
aeration for maximum yeast growth are not good methods for making
tasty beer. As you probably know, some brewers would like to avoid
aerating the wort entirely, as undesirable oxidation products can be
produced by wort aeration prior to fermentation.
You may be hinting at the bigger question I mentioned above, i.e., to
determine how much oxygen is best for making beer if only a single
aeration/oxygenation is performed. That is no small undertaking.
(Incidentally, one should always remember that air/oxygen is in the
headspace of the fermentor after the aeration is finished, and this
headspace continues to be a source of oxygen for the yeast until they
finally consume it or blow it off.
Fred L Johnson
Apex, North Carolina, USA
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Date: Wed, 7 May 2008 10:54:32 -0400
From: "Lemcke Keith" <klemcke at siebelinstitute.com>
Subject: Video from Big Brew Day
For those HBD members looking to plan for next year's AHA Big Brew Day,
the event held here in Chicago at the home of Randy Mosher & Nancy Klein
shows how to "do it up right"! Despite cool weather, the amazing food &
beer propelled brewers & beer lovers through a terrific day. You can see
the video highlights on YouTube at
http://www.youtube.com/watch?v=-uscDiuthHA , and check out the other Big
Brew Day videos while you are there.
Thanks, Nancy & Randy!!!
Keith Lemcke
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End of HOMEBREW Digest #5330, 05/07/08
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