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Old 12-14-2012, 09:43 PM   #11
ajdelange
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Originally Posted by lockwom View Post
I'm especially interested where the formulae fail in underestimation. I recently brewed a Lil Sumpin Sumpin (Lagunitas) clone where Rager estimated 40s, and Tinseth 30s, but Lagunitas claims 65, and Jamil translated hop additions straight from their brewers.
I don't think it's the formulae. I think it's that you don't have good data to put into the formulae.

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Beer color can be decently collapsed to one dimension like SRM.
I'd be interested in hearing how you came to that conclusion. The statement is perfectly true but not many people are aware of this (AFAIK).

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Limiting IBUs to hops and not other factors like minerals really 'dilutes' the value of the metric.
I offer without comment the first paragraph of the relevant MOA:

"Reports of the Subcommittee on Determination of
Isohumulones in Beer for 1967 and 1968 (Ref. 1) indicate
that bitterness units (BU), as determined in Method
A below, express the bitter flavor of beer satisfactorily,
regardless of whether the beer was made with fresh or
old hops. The European Brewery Convention has
adopted the “E.B.C. Bitterness Units,” determined in a
similar way, as a uniform method that best expresses the
true bitter flavor value of beer."
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Old 12-14-2012, 10:33 PM   #12
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I'd be interested in hearing how you came to that conclusion. The statement is perfectly true but not many people are aware of this (AFAIK).
Most of what I've read about SRM/Lovibond was in Daniels's book. I didn't feel like I knew enough on the subject to unilaterally claim the measure's perfection, but I am happy to learn.

As for IBU's intent vs my criticism: I respect the measure's repeatability, but ultimately bitterness is perceived. So my claim relates more to the fact that a heavily hopped recipe made with Burton style water would taste different with purer water like Pilsen's.

Kai, I really respect your work, especially your awareness of German homebrew techniques. Do they use different approaches?
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Old 12-15-2012, 12:45 PM   #13
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There are some parallels and some differences in color and bitterness. Both are, of course, perceptions and both are expressed with a single number and the single number, while it does give some indication as to what one will experience is far from the whole story. To convert SRM (which represents the optical absorption of the beer at one wavelength i.e. a repeatable physical measurement) to a perceived color one must convert the SRM to the absorbtion spectrum of the beer. Noting that a kriek and a lambic may have the same SRM it is clear that the SRM alone doesn't tell the whole story. A couple of 'spectral deviation coefficients' complete the spectrum picture at which point we have to consider the color of the illuminating light, the width of the glass....

With bitterness the IBU number, also based on a physical mesurement - the concentration of isolhumulone - gives a picture of bitterness but not a complete one. There is the fine bitterness of Saaz and the coarse bitterness of the high alpha cultivars. And then the differences in perception that come, again along the fine/coarse 'axis' with respect to the presence of sulfate.

The big difference between the two is that there is lots of science available to describe the spectral difference between kriek and brown ale of the same SRM and how to convert SRM plus SDCs (spectral deviation coefficients) to visible color taking viewing light quality and path into account. Similar science does not, AFAIK, exist for bitterness but there are people working on it.

I guess I feel that beer color, IBU readings and pH should be used in the same way as OG, FG, TE, ABV and attenuation numbers and that is as checks that you made the beer you were trying to make. If all those numbers come out close to what you have obtained other times you brewed the same beer then there is a pretty good chance that this beer will meet your expectations. If one or more of them is way off there is a pretty good chance that it won't.

As most home brewers and small craft brewers do not measure any of those parameters except OG and FG the value of calculating IBU and color based on formulae seems to have limited value as the formulae for neither are particularly good predictors and as I have noted before I think that is not so much because the formulae are wrong as it is that you don't have good data available to plug into them. FWIW over an ensemble of 23 beers with IBU's ranging from 12 to 36 I found rms error of 5.1 IBU (including a bias of 2.2 IBU) from the Tinseth formula with the time dependence parameter adjusted for minumum IBU (not time and OG parameters as I indicated in an earlier post). Those of you familiar with error analysis will be saying to yourselves 'Why didn't he back the bias out?' I could, of course, do that but it would add another parameter to the formula, I don't, based on 23 beers, have much confidence that 2.2 is the right bias number and if I do back it out of these beers it only drops the rmse to 4.6 IBU.

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