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Old 04-25-2013, 02:24 PM   #11
Aug 2010
McLean/Ogden, Virginia/Quebec
Posts: 9,298
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Originally Posted by boomernintysix View Post
I have seen it once with bud/miller/coors vs Guinness. As you would expect the big three are pale yellow and Guinness is this beautiful pale-ish red color (all at 430).
I'm not sure what it is that you are describing but Bud and Guiness are actually pretty similar in color if you adjust the paths so that the absorption at 430 nm is about the same. As I said in an earlier post a couple of feet of Bud and a mm or so if Guiness would look pretty similar. I've put a graph of the normalized absorption spectra of Guiness, Bud, Tsing Tao and Lindeman's Kriek below. The blue curve is the average normalized spectrum of an ensemble of 99 beers. As you can see the three 'normal' beers have spectra quite close to the average spectrum. The Kriek does not.

The amount of deviation from the average spectrum can be quantified. This is the basis for the Augmented SRM method. Instead of just saying that Bud has an SRM of 2.40 you also add the Spectrum Deviation Coefficients (SDC): -0.911, + 0.19 and -0.04. That's a complete (if not 100% accurate) spec for the color of Bud. Guiness has an SRM of 51.88 but its SDCs are 0.551 -0.153 and 0.054. Lindemans Kriek has SRM 15.27 with SDCs +1.784, 0.788 and -0.074. Thus the color characteristics, expressed in terms of the difference from the color characteristics of an average beer, are small except in the case of fruit beers. A typical all malt beer has a first SDC of about -0.6. Thus Bud and Tsing Tao are typical but Guiness, with it's first SDC of + 0.55 is more Kriek like than Tsing Tao and Bud.

If you had a normal malt beer at 15.27 SRM (same as Lindeman's Kriek) but with first SDC of around - 0.6 it's obviously going to look quite different from Kriek with a first SDC of +1.78. OTOH any other beer with an SRM of 15.27 with first SDC near -0.7 (all malt beers) is going to look pretty similar with the actual distance in color space depending on the path, the full set of SDC's, the chosen color space, the illuminant and the 'observer' (one of 2 promulgated by the CIE).

Originally Posted by boomernintysix View Post
I need to read up on Tristimulus more but most the texts I have found are either "who really cares" or its just way over my head. I feel like accurate color assessment is one of those "arts" in brewing where science leaves us lacking.
Commercial brewers care about it a great deal because, especially in the case of beers like Bud, the very light color is hard to get and is very much a part of the brand. Were the color perceptibly different from batch to batch consumers would notice. Craft brewers don't seem to care so much. Most home brewers don't but some, i.e. those with a geeky bent, find it a fascinating subject.

It is true that to understand what Tristimulus tells you you need to know more about color than what your kindergarten teacher taught you about color wheels and it is also true that the math can get pretty hairy.

The science is thus there but it is not fully appreciated. I proposed the Augmented SRM method to ASBC as it gives full color information about a beer under any viewing conditions and requires math very similar to the math required by the tristimulus method. A guy who was present when the committe considered it told me that no there understood what was involved. These things take time.
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