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HOMEBREW Digest #5201
HOMEBREW Digest #5201 Sun 01 July 2007
FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
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Contents:
ASBC Presentation ("A.J deLange")
Bottling with a slight Brett infection? (Bill Velek)
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Date: Sat, 30 Jun 2007 16:36:00 +0000
From: "A.J deLange" <ajdel at cox.net>
Subject: ASBC Presentation
Many thanks to Scott for the kind words (enjoyed the chat and beer with
you). As what I presented to ASBC started right here with HBD
discussions it seems appropriate that I tell you, gentle readers,
something about it. Consider the following three assumptions: (1) Beer
obeys the Bougert-Beer-Lambert law. (2) Beer is an "ideally dilute
solution" of coloring and other substances (3) The coloring substances
are in fixed concentrations relative to one another irrespective of the
amount of color in the beer.
Number (1) says that the absorption (log of the ratio of the amount of
light entering the sample to the amount leaving it) of light at
wavelength lambda caused by substance i is Ai(lambda) =
d*ci*ei(lambda) where d is the length of the path of the light beam
through the sample, ci is the concentration of substance i in moles per
liter and ei(lambda) is the absorption coefficient for substance i at
wavelength lambda. Number (2) says the color forming (and other)
dissolved substances act independently of one another so that the
absorption at wavelength lambda is A(lambda) =
d*sum_over_i(ci*ei(lambda)). Number (3) says that ci = ri*c0 where ri
is the ratio of the concentration of substance i to the concentration,
c0, of substance 0 which implies that A(lambda) =
d*c0*sum_over_i(ri*ei(lambda)).
If these assumptions are valid and we divide the absorption at each
wavelength by the absorption at 430 nm (other wavelengths could be used)
we get A(lambda)/A(430) =
d*c0*sum_over_i(ri*ei(lambda))/d*c0*sum_over_i(ri*ei(430)) =
sum_over_i(ri*ei(lambda))/sum_over_i(ri*ei(430)) which is a constant for
each wavelength dependent only on the relative concentrations of the
colorants and their absorption coefficients but not on the overall
concentration which is completely specified by c0. Thus, all beer
absorption spectra, when normalized by their absorption at a particular
wave length are the same. The implication of this is that the absorption
spectrum of any beer can be completely specified by the absorption at
430 nm if one knows A(lambda)/A(430) for any other (i.e. a reference)
beer. Given the entire spectrum one can calculate actual visible colors
by the method of ASTM E-308 which John Viggiano summarized tidily in HBD
#5183. Bottom line: Given that (1), (2) and (3) hold, the SRM number
(which is simply 12.7*A(430)) is sufficient to completely specify the
color of a beer.
So are (1), (2) and (3) all true? Doubtless no and we don't really care
whether they are or not. What we care about is whether the normalized
spectra behave as if they are (i.e. whether these assumptions serve as
a good model for actual behavior). In fact the deviations of normalized
beer spectra from an average normalized spectrum (obtained from an
ensemble of beers) are quite small, so small in fact that they can
easily be encoded by 2 or 3 numbers I call Spectral Deviation
Coefficients but which are, in fact Principal Components, obtained by
projecting the beer's actual deviation from the average spectrum onto
Eigenvectors obtained from analysis of the same ensemble from which the
average spectrum came. The capitalized words are big ones that will be
unfamiliar to most but that should not be an issue. Spectral Deviation
Coefficients are easily calculated from tabulated values of eigenvectors
and it would be the responsibility of the ASBC, should they decide to
accept my proposal, to supply brewers with these tabulated values (and
with tabulated values for the average spectrum). Let me note that there
is no more complexity here than in their current Method of Analysis, MOA
Beer-10C, which calculates visible (tristimulus) color for one set of
viewing conditions (with the complete spectrum available one can
calculate visible color for any viewing conditions). The actual
calculations for Beer -10C are done with a simple spreadsheet and the
SDCs can be calculated with a similar spreadsheet.
You are doubtless all asking yourselves "How did he ever think of this?"
Well, I didn't. Miller and Stone in their 1949 paper proposing the SRM
(now known as MOA Beer-10A and very similar to the EBC method)
normalized the absorption spectrum by the 430 nm value and indicated
that if the normalized spectrum deviated more than a certain amount from
the average normalized spectrum that the beer was not eligible for color
characterization by the SRM. Thus, though they may not have fully
appreciated what they were doing, they came up with a measure which is
capable of completely specifying the color of eligible beers with a
single number. What's new here is encoding the spectral deviations so
that beers which don't pass Miller and Stone's test can also be
completely characterized with respect to their colors.
In summary I am proposing that the ASBC promulgate a new MOA (Beer-10x
?) which would include tabulated values of an average normalized
spectrum and 2 or 3 eigenvectors. The numbers that go into these table
would be determined by analysis of an ensemble of beers selected by the
Society. Brewers would measure the spectrum of a beer in 1cm and
multiply the 430 nm reading by 12.7 to compute the SRM as has been done
for almost 60 years. They would then normalize the 1 cm spectrum by the
430 nm reading and subtract the average spectrum. This is the deviation.
It is multiplied pointwize by each of the eigenvectors and the products
for each eigenvector accumulated. The resulting 2 or 3 numbers are the
SDCs. Thus instead of characterizing the color of Moretti by SRM 3.3 we
would characterize it as SRM: 3.3, SDC1: 0.164, SDC2: -0.0004.
Pilsner Urquell would be SRM: 5.9, SDC1: 0.308, SDC2: -0.012 and
Newcastle Brown Ale as SRM: 28.7, SDC1: -0.032, SDC2: -0.036. The
familiar SRM is retained and visible color in any path under any
illumination can be calculated from the full spectrum reconstructed from
SDCs and SRM by the reverse of the process just descibed.
That's the story. I'm happy to answer questions and forward a set of the
slides used in the presentation to anyone who wants them. I can also
send along a copy of the Excel spreadsheet which calculates SDCs from
input spectra (useful only to people who have access to a
spectrophotometer or beer spectrum data) and which calculates beer
colors (in CIELAB space) from SRM, SDCs and path for several common
illuminants. If you don't have SDCs this will calculate an approximation
to the color which will be good if the beer is close to being
"average" (like Newcastle with it's small SDC's) and not so good if it
isn't.
A.J.
------------------------------
Date: Sat, 30 Jun 2007 13:57:00 -0500
From: Bill Velek <billvelek at alltel.net>
Subject: Bottling with a slight Brett infection?
In Homebrew Digest #5199, Doug Moyer wrote:
> Subject: Fighting infection with Campden tablets
>
> My latest batch (a low alcohol hoppy brown ale)
> developed a white pelicle during fermentation.
snip
> There are a couple of dots on
> the surface, so there is obviously still some
> infection.
>
> I want to keg the beer tomorrow. Can I use Campden
> tablets to prevent further infection? (I understand
> that any infection byproducts are not going to
> magically disappear with the addition of the Campden
> tablets...)
>
> If that will work, how much should I use for five
> gallons? I assume I would crush the tablets and add
> them to the keg before filling. Correct?
As a matter of fact, I'd like to hear about this, too. I just bottled
two carboys a couple of days ago; both of them had also developed a
white pellicle, which didn't really concern me because I've often had a
film floating on my wort. As usual, I used a wine thief to taste each
one before preparing a starter and sanitizing my bottles; years ago I
had prep'ed everything to bottle a batch, only to discover that it was
so infected and phenolic that it needed to be tossed. That will never
happen to me again; word to the wise -- test your beer before preparing
to bottle.
Anyway, when I drew my samples this time, I noticed a somewhat vinegary
smell, so I don't know if I have an acetobacterial infection, or a Brett
infection, or if there is any difference. I do know that the pellicle
was not anything like mother of vinegar, and there was only a _very_
slight sourness so the beer tasted pretty good. I decided to take my
chances and bottle because I've had homebrewers tell me that the few
batches that I've tossed over the years might have turned out okay if I
had just given them a chance to age a bit.
Now, I do have a question that is slightly different from Doug, who is
kegging and can force carbonate; I still bottle, so I need to know if
hitting the batch with some PotMet or whatever is going to hurt the
yeast. And is there a time period to wait between applying the PotMet
and bottling, in order to allow the sulfur to vent? Or can it just be
bottled?
Thanks for any info.
Bill Velek - Grow hops? See http://tinyurl.com/3au2uv w/250+ members. To
discuss 'equipment only' w/640+ homebrewers see http://tinyurl.com/axuol
and to join 'Homebrewers' to help mankind see http://tinyurl.com/yjlnyv
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End of HOMEBREW Digest #5201, 07/01/07
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