HOMEBREW Digest #5201 Sun 01 July 2007

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  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. Return to table of contents
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 Return to table of contents
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