HOMEBREW Digest #5052 Wed 06 September 2006

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  re: Beer and Beer's Law (was: Color Extraction) ("steve.alexander")
  lactose in sweet stout (Robin Griller)
  Beers Law & color ("A.J deLange")
  Re: Beer and Beer's Law (was: Color Extraction) (J A Stephen Viggiano)
  Re: Beer's law and linearity (J A Stephen Viggiano)
  Beer-Lambert (mabrooks)

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---------------------------------------------------------------------- Date: Wed, 06 Sep 2006 01:05:25 -0400 From: "steve.alexander" <-s at adelphia.net> Subject: re: Beer and Beer's Law (was: Color Extraction) J A Stephen Viggiano agrees with AJ's recent note that beer may indeed follow beers law *BUT* let me note this may be a result based on too small a sample space. AJ used Guinness as I recall and JohnV notes that he uses ... "Beamish Stout at five different concentrations", but dark stouts owe their color to roast barley or malt roast to a black char color probably with large amount of color from carbon, and this is not typical of other beer styles. Based on what I read of Debye-Huckel (and I only learned Deybe- Sommerfeld at school - rats) and several other effects mentioned by AJ, it seems likely to me that the color of the phenolic compounds in beer and possibly of some Maillard products would be most likely to demonstrate the non-linearity of the "beer does not follow beers law" aphorism. It's easy enough to find test beers reasonably dark from caramel and maillard products, but it's a bit more difficult to think of beers with significant phenolic color. I suppose that wider cuvettes of a pils might do but that's a guess. May I challenge you to fire up your spectrometers on samples of a beers with more typical coloring agents than stouts ? tnx, -S Return to table of contents
Date: Wed, 6 Sep 2006 08:13:58 -0400 From: Robin Griller <rgriller at chass.utoronto.ca> Subject: lactose in sweet stout I've brewed sweet stouts on several occasions and have always used a little over 1 lb./5.25 gallon recipe. I wouldn't say that lactose makes the beer that sweet in any case -- it more gives it a fullness and keeps it from being dry. Robin Return to table of contents
Date: Wed, 06 Sep 2006 13:00:32 +0000 From: "A.J deLange" <ajdel at cox.net> Subject: Beers Law & color When this thread originally kicked off I did an initial check with the beer that was most handy which was an Oktoberfest of 17.6 SRM. The linearity was good which caused me to do the Guiness based on the thought that perhaps the coloring material in the O'fest was too dilute to show deviation from "ideally dilute" behavior. I also thought about the spectrophotometer I use. It is programmed with hundreds of "methods" the very great majority of which are based on Beer's law i.e. the instrument stores an absorbtion coefficient which is multiplied by the measured absorbtion to give a reading directly in concentration. Those methods that tabulate polynomials or piecewize linear functions of for concentration vs. absorbtion are typically those where it is not depth of color that is being measured but rather the scattering of light in a precipitate (for example, to measure sulfate, barium chloride is added to the sample and the amount of light which passes through the resulting cloud of barium sulfate is precipitate measured). Thus it appears that Beers law is generally followed with rare exception. Why would we suppose beer to be an exception? Up to this point it's because of the lore. Looking at the collection of articles in the link Peter Ensminger posted a week or so back I realized that not everyone accepted that beer was an exception even then. It appears at this point that I was taken in by a ****** [an apparently offensive word, as my post was rejected because of it, removed - wondered why I hadn't seen it recently]. OTOH no less an authority than Jean DeClerk wrote "This law, however, is not universally applicable. It is only true with low concentrations (less than 0.6M)..." (Vol II p 253). And John didn't prove that beer follows it. He proved that Beamish stout follows it. Nor did I prove it with Guiness or the O'Fest. These are, at this point, anecdotal results.The jury is still out. The broader question, posed by Nathaniel, is what this has to do with beer color. Determination of beer color has an interesting history. The motivation behind specifying beer color was to have something which could be measured in the laboratory. Before the days of spectrophotometers that was a tall order. The original attempts involved comparison with iodine solutions of various strengths and I think the Lovibond series arose from that general concept. With the advent of decent photometers after WWII the ASBC moved to an instrumental method which would not depend on subjective judgement of match using north light in the early afternoon. The SRM method was the result and conceptually it is seriously flawed (it is the SRM measurement we are talking about here). It was based on the average spectral characteristics of a couple of dozzen pale American beers and the words in the MOA say it applies only to beers of "average spectral characteristics". Thus, technically, Guiness does not have an SRM rating. Further the SRM is a single number and as we all know it takes at least 3 numbers to specify a color. For me to tell you what color a beer will appear to you as you hold the glass up to the light you must tell me 3 absorbtions, the thickness of the light path through the beer and the color quality of the light. It's best if you tell me the spectral absorbtion of the beer every 5 nm over the visible range. From that, given the path and the illuminant, I can calculate a tristimulus - i.e. the color you see. Now beer is very interesting. It's absorbtion spectra are all very similar. Most (99%) of the variation in spectral properties over beers as diverse as Bud light to Watney's stout and including Lindeman's Kriek can be modeled by a single number (principal component) and 99.9% by four. Interestingly enough the first principal component correlates with the SRM value for the beer very, very well (Pearsons r = 0.99934). Thus if you tell me the SRM number I can calculate the first principal component and thus the spectal absorbtion curve for the beer. I can adjust this for any path and any illuminant and tell you what color you will see in the glass. If you give me the other 3 components I can tell you the color to an accuracy of 3 units in L*ab space. Thus the SRM number actually turns out to be more valuable than it might first appear. Return to table of contents
Date: Wed, 06 Sep 2006 10:57:46 -0400 From: J A Stephen Viggiano <jasv at acolyte-color.com> Subject: Re: Beer and Beer's Law (was: Color Extraction) "steve.alexander" wrote: > Based on what I read of Debye-Huckel (and I only learned Deybe- > Sommerfeld at school - rats) and several other effects mentioned by > AJ, it seems likely to me that the color of the phenolic compounds in > beer and possibly of some Maillard products would be most likely to > demonstrate the non-linearity of the "beer does not follow beers law" > aphorism. Beer does not obey the Bouguer-Lambert-Beer law if it is visibly turbid. Kubelka-Munk would probably deal with that. ASBC Method of Analysis Beer-10 (Color) stresses the importance of degassing the sample prior to measurement. Don't forget about the bubbles. > May I challenge you to fire up your spectrometers on samples of a > beers with more typical coloring agents than stouts ? I also have a nice plot of Beck's Oktoberfest at a number of concentrations. As with my Beamish plot, it's not just at 430 nanometers, but at 400, 410, ..., 700 nm. It was produced using a different spectrophotometer, a Macbeth Color Eye 7000, which is a single-beam instrument that is limited to about 2 Absorbance. ==John Return to table of contents
Date: Wed, 06 Sep 2006 11:25:26 -0400 From: J A Stephen Viggiano <jasv at acolyte-color.com> Subject: Re: Beer's law and linearity Nathaniel Lansing wrote: > Does a beer that measures 10 SRM appear twice > as dark as the beer that measures 5 SRM? Just about, but a 30 SRM does not appear twice as dark as a 15. As you point out, SRM is logarithmic. The Lovibond Tintometer scale is logarithmic, as well. This was so that one could add, for example, use a combination of 2.0 units of Yellow and 3.0 units of Yellow and obtain the same result as 5.0 units of Yellow. The Series 52 scale is a bit different, as a decreasing proportion of "Red" is used as the amount of Yellow increases -- corresponding to a negative correlation between SRM and Linner Hue Index, but my impression is that the Yellow scale was linear in Absorbance. Also, as you point out, the response of the human visual system is not logarithmic. The 0.4 power relationship you mention is quite close to the 0.43 used by Ebner and Fairchild (Proceedings 6th Color Imaging Conference, 1998). The relationship which is most widely accepted today is Pauli's extension of the Reilly cube root function, upon which the correlate of Lightness in the CIELUV and CIELAB uniform color spaces are based: L* = 116 * (Y/Yn) ** (1/3) - 16, Y/Yn > (6/29) ** 3 L* = (29/3) ** 3 * (Y/Yn), Y/Yn <= (6/29) ** 3 where Y/Yn is the luminous reflectance or transmittance, and L* is the Lightness. This implies SRMs are visually closer for darker beers than for lighter, which is how they actually appear. I had produced a series of color standards for training beer judges. They were at 5 SRM, 10 SRM, 15 SRM, and 20 SRM. I verified the SRM rating of each using a spectrophotometer, and each measured within 1/10 SRM unit (1/20 unit for the 5 SRM standard). We poured small samples of each into identical sample jars, lined them up, and viewed them. The difference between the 5 and 10 SRM samples was perceptually large; between the 15 and 20 samples, much smaller. SRM was intended to be only roughly visually uniform; cross-functionality with the Lovibond Series 52 scale was also an issue. ==John Return to table of contents
Date: Wed, 6 Sep 2006 10:09:30 -0700 (PDT) From: mabrooks <mabrooks12 at yahoo.com> Subject: Beer-Lambert In a recent posting: >Date: Mon, 4 Sep 2006 15:27:09 -0400 (EDT) From: J A Stephen Viggiano <jav9729 at cis.rit.edu> Subject: Beer and Beer's Law (was: Color Extraction) In archive 5046, on 19 August, A.J deLange asserted that "beer doesn't follow Beer's law". Or, more precisely, I suppose he repeated this assertion. So it's not my intention to single out A J; many people have repeated what experimental evidence has shown to be an urban legend. I had recently looked into this very question, and have determined that if the beer is free of visible turbidity, it does indeed obey the Bouguer-Lambert-Beer law (to give it its full name). - ------------------------------------------------------- I did not take the time to research AJ's post, however, I am in agreement in the statement that beer color does not follow the Beer -Lambert and cannot due to the following: The Beer-Lambert Law states that: A =abc where: A= Absorbance a= species apparent absorption capabilities b= pathlength c= species concentration Can anyone tell me what the concentration of a "color" is in a beer? No, not hardly(unless they used a precisely measured amount of pigment dye to color it?)...why, because there does not exist any standards by which to measure a color concentration. Color absorption yes, color concentration, NO! The Beer -Lambert law is specifically for determining concentration of a species in solution, by combining two laws. Separate the two laws and what you find is: Lambert's law explains that, in solutions, each layer of equal thickness absorbs an equal fraction of light which transverses it, thus, when a ray of light passes through an absorptive medium (beer), its intensity decreases exponentially as the length of the medium decreases. Hence when dealing with dilute "color" concentrations in solution, one must be careful to select a "path length" that will allow proper determination of the solutes "color". High concentrations = smaller path lengths whereas very low concentrations will require longer path lengths. Beers law states that: the intensity of a ray of monochromatic light decreases as the "concentration" of the absorbing medium increases. It is important to note that not all colored solutions obey Beers law (Test question: can anyone tell me when/why it wouldn't) so new colorimetric methods may need to be developed to measure these. So what you have with the Beer-Lambert is the combining of two laws for the determination of concentrations of solute in solution. Beer color does not follow the Beer-Lambert law, as you are only measuring color, not concentration! Color determination will follow the Lambert law to some extent, as that is what is is mostly used for. There is much, much, more detail to present to here, but prob not needed/wanted by the masses. It is imoportant to note that a Spectrophotometer must be set up properly so it is measuring the proper absorptive wavelength. To do this and one must know what this wavelength is before beginning the analysis, hence the original solution (beer) needs to be diluted down, and a full spectrum analysis performed to determine the wavelength of maximum absorbance etc..... unfortunately one can, at best, only come up with a comparison chart to use against other beers whose colors "wavelength of maximum absorbance" falls within the exact same wavelength as the benchmark beer(chances are slim to none this will occur), so I dont see any real benefit from going through all the trouble? Matt B. Northern VA. Return to table of contents
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