The Briess/Fix Homebrew SRM Color Test method revisited

Silver_Is_Money · Oct 15, 2017

Back in the days when Michelob Classic Dark was still available Dr. George Fix developed a method for reliably determining your beers SRM color via matching it against a 17 SRM 'standard' beer (wherein he used Michelob Classic Dark as his reliable 17 SRM standard) diluted volume for volume with distilled water to various concentrations. The relationship can be seen below. All that is required is a beer with a repeatable and confidently known 17 SRM color to revive this relatively simple comparison method. Dilute the 17 SRM beer and pour some into a clear glass or test tube, then poor your homebrew into an identical glass or test tube to the same level, and compare their colors. Or better yet, pour your homebrew into the test vessel and then dilute the 17 SRM beer 'standard' until when poured into a matching test vessel and to the same level they make a color match. The comparison is best done when both beers are degassed, or flat. Does anyone know of a highly confident to be consistently brewed or blended commercial beer at the same 17 SRM color that can replace Michelob Classic Dark as the 17 SRM color standard?

SRM Color of various dilutions of Michelob Classic Dark (17 SRM)
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2 SRM @ 6.9% by volume
3 SRM @ 11.1% by volume
4 SRM @ 14.5% by volume
5 SRM @ 17.5% by volume
6 SRM @ 20.2% by volume
7 SRM @ 22.9% by volume
8 SRM @ 25.9% by volume
9 SRM @ 29.2% by volume
10 SRM @ 33.3% by volume
11 SRM @ 38.3% by volume
12 SRM @ 44.3% by volume
13 SRM @ 51.8% by volume
14 SRM @ 60.8% by volume
15 SRM @ 71.6% by volume
16 SRM @ 84.5% by volume
17 SRM @ 100.0% by volume

Reference source: http://brewery.org/library/Color.html

PS: In researching this I read somewhere wherein the mega-breweries are capable of consistently holding their products SRM colors to within 0.1 of their target. I doubt that a micro-brewery could hold color to such a tight tolerance. It's perhaps +/- 0.5 to 1.0 SRM for most of them.

ajdelange · Oct 15, 2017

No. I did look into this a couple of years ago. Visual comparison has some limitations as while the SRM number contains an amazingly large proportion of the total information about the color of the beer it does not contain 100% of it an Michelob Classic Dark's secondary color parameters are (were) not the same as those of all beers comparisons to other beers would be at best approximate (which is, of course, good enough for most home brewing application). I used to think that Guiness might serve as a standard but later found they aren't as consistent as I thought.

Rather than using a beer as the reference for comparison I would suggest using photographic neutral density filters as their attenuation at 430 nm is known (as it is for any other wavelength. One cm of a 12.7 SRM beer attenuates 430 nm light by 1.0. So does a 1.0 neutral density filter. Were one to place a 1 cm cuvet of such a beer in front of a uniform light source (a good light table tipped vertical) and compare its color, AS VIEWED THROUGH A BLUE FILTER, to a series of neutral density filters one might get a fair estimate of the SRM of the beer. If it were closest to an 0.3 ND (1 stop) filter we would estimate SRM as 0.3*12.7 = 3.81. If closest to a 0.6 ND (2 stops) density filter, 0.6*12.7 = 7.62 and so on. One used to be able to buy 'step tablets' which were strips of film with patches of different densities printed on them but I expect those would be pretty hard to find these days. ND filters are still readily available.

The blue filter mentioned above is necessary to remove the effects of the beer's color at other than 430 nm to the extent possible. A bandpass filter centered at 430 nm would be ideal and these are available from Edmund but be aware that a really narrow filter looks like a mirror. It does not pass much light so a blue color separation filter (which one used to be able to readily obtain from Kodak, for example) will probably have to serve.

Of course one would apply Beer-Lambert to different path lengths and dilutions in order to accommodate a range of beers with the filters at hand.

This is an off the top of my head idea (though I have used ND strips to calibrate a simple electronic SRM meter I made from an Arduino board) so it might prove not to work at all as well as one might hope but it's probably worth experimenting with.

Silver_Is_Money · Oct 15, 2017

I wonder what the current SRM is for Newcastle Brown Ale? I'm aware that in 2015 they were forced to remove the caramel colorant they added to it when (as I recall) it went onto the suspected carcinogen list. That change required re-formulation, and may have impacted the color (as well as the flavor), but whatever its color is today it should be pretty well controlled and consistent. My initial guess is 15 SRM.

ajdelange · Oct 15, 2017

Yes, but how would you know that they haven't had another regulatory issue or determined from a focus group that their consumers prefer it a little lighter (or darker).

How a about Sinamar? That's now available from many LHBSs and at least comes specified to have a certain SRM. Dark as it is you would be able to cover a wide range of beer color values. It's spectral properties are very similar to beer's and if you use the blue filter trick you can probably even cover things like Krieks with it.

Only potential problem I see is the necessity to have some pretty accurate means for measuring out small quantities of it in order to make the dilutions required for comparison. Good mixing cylinders, volumetric flasks, pipets etc.

Silver_Is_Money · Oct 15, 2017

ajdelange said:
How a about Sinamar? That's now available from many LHBSs and at least comes specified to have a certain SRM. Dark as it is you would be able to cover a wide range of beer color values. It's spectral properties are very similar to beer's and if you use the blue filter trick you can probably even cover things like Krieks with it.

Only potential problem I see is the necessity to have some pretty accurate means for measuring out small quantities of it in order to make the dilutions required for comparison. Good mixing cylinders, volumetric flasks, pipets etc.

That would be the ticket. All that would be required would be to initially determine how much of it to add to a quart (or gallon, liter, etc...) of water to bring it to 17 SRM, then this would become the new 17 SRM standard.

Or better yet, how much to add to come up with SRM standards ranging from 2 through 25 (and beyond).

ajdelange · Oct 15, 2017

Sinamar is specified at 8100 - 8600 EBC 4115 - 4369 SRM. Thus to attain 17 SRM you would have dilute it by 241:1 to 256:1 with DI water. Assuming most bottles fall around the halfway point between the extremes that would be 8350 EBC or 4242 SRM requiring 248.5:1 dilution for 17 SRM. But why 17? You can dilute it to any value you want: 4214/SRM -1: 1. For eample, if you know your beer is between 10 and 20 SRM it seems a 4214/20 -1: 1 i.e. 211:1 dilution for a 20 SRM solution would make sense. You would put 50 mL of that in one container and the beer in another identical container and add DI water to the beer until you got a match. SRM = 20*50/(50 + volume_dilution_water).