Anybody know how SRM is calculated?

How is the Standard Reference Method of a beer calculated? I have seen beers with SRM's that I would swear are not correct, but what do I know. How is color measured?

In the 1950s it was discovered that for pale beers absorbance so measured was essentially proportional to visual units like the Lovibond scale. In 1958, the American Society of Brewing Chemists proposed that the absorbance of beer in a 1/2" ID jar using a monochromatic light with a wavelength of 430 nm be used; the procedure was called the Standard Reference Method (SRM). They proposed a correction factor of 10 so the numbers reported would match up with the Lovibond scale. Commercial beer brewed at this time was almost always below 4 Lov., and hence SRM became viewed as an equivalent of Lov.

Click to expand...

http://ourworld.compuserve.com/homepages/wrucksterpage/color.htm

hialtitude said:

How is the Standard Reference Method of a beer calculated? I have seen beers with SRM's that I would swear are not correct, but what do I know. How is color measured?

Click to expand...

Are you talking about homebrews? You can estimate SRM through formulas using the ingredients in the recipe (formulas I do not know), but color will also be impacted by procedure. Smaller boil size, for example, leads to more caramelization, i.e. darker color. Same with doing a 90-minute boil. The color you get from liquid extract will be a function in part of how old it is.

Sorry, it looks like I need to clarify.

My question is regarding both homebrew and micro/craft/macro, etc.

Do breweries send samples to a lab to calculate SRM? Or can they calculate that in house? What does that process involve?

If a homebrewer wanted to calculate SRM, would they have to approximate it, or is there a definitive way to measure?

I don't have any hidden agenda here, I have just always been mystified about how color is measured. Some beers boast a SRM that I would not expect when compared to others. I saw some technical writing regarding the method, but would like to know what peoples experiences have been getting a beer measured.

You need to know the SRM (or lovibond) values for your individual malts, but it's easy to calculate the value for your beer.

For each grain calculate:
(grainWeightInLbs * grainSRM) / batchSizeInGallons

Then just add up all the results.

Eg).
batch: 5 gallons
pale malt: 8lbs @ 2SRM
crystal malt: 1.5lbs @ 20SRM

[(8 * 2) / 5] + [(1.5 * 20) / 5] = 9.2 SRM

There are actually a few formulas for calculating (IBU's has a similar 'problem') but this is the simplest. The key is to pick a formula and stick with it. For example in the software I'm writing I'm defaulting to the Morey formula at the moment.