I've done a lot of snooping around about how to measure beer color in the last couple months, and want to share what I've learned with the community. Although how to measure color probably doesn't qualify as a "frequently asked question", I think this info is worth preserving in the archives to save others research time.
Below is a draft of a FAQ on measuring beer color; I've never written a FAQ before and welcome comments on this draft. Is it worth putting this in the archive? Should it be a FAQ or just a treatise? Any suggestions for improvements?
Proposed FAQ: Measuring Beer Color v0.1 Last modified 9/28/94
Beers range from almost colorless (American light lagers) to almost black (stouts and porters). I wanted to begin quantifying the colors of my beer to aid in fine tuning my recipes. This FAQ summarizes what I've learned so far. Please send suggestions or corrections to firstname.lastname@example.org.
Dr. George Fix has written an excellent article on beer color, posted to Home Brew Digest #1328 which is archived at sierra.stanford.edu. Much of this FAQ is derived from this article.
Q: What units are used to quantify beer color?
A: There are currently two color scales in common use: SRM in the US, and EBC in Europe. The SRM scale is based on an older scale called degrees Lovibond, and for all practical purposes SRM and degL are identical. SRM and EBC are not linearly related. However, the following equations are reasonably good below SRM 4:
EBC = 2.65 x SRM - 1.2 SRM = 0.377 x EBC + 0.45Unfortunately most beers other than light lagers have color darker than SRM 4.
Q: How is color measured?
In professional brewerys, color is measured photometrically. The equipment to carry out the measurement is expensive and this isn't a practical solution for homebrewers.
Probably the best way is to compare against commercial beers of known color. The following list was combined from a number of sources. Please send corrections or additions to the FAQ author (email@example.com).
Beer SRM ------------------------------ Budweiser 2 Miller 3 Molson Export Ale 4 Pilsner Urquel 4.2 Spaten Club Weiss 4.6 EKU 5 Ottobeurer Fest 7 Anchor Steam 9 Bass Pale Ale 10 Whitbread Pale Ale 11 Noche Bueno 13 Michelob Classic Dark 17 Salvator (Paulaner) 21 Triumphater (Lowenbrau) 29 Beliken Stout 76Depending on where you live, collecting a range of commercial beer samples can be difficult and expensive. Fortunately, it's possible for a single individual to use commercial beers to derive cheaper/easier to find secondary standards.
1. Dennis Davison compared colored photographic filters against commercial beers to make a calibrated set of color swatches. He sells a film card with the color swatches for a modest fee. Send email to firstname.lastname@example.org for info.
2. Briess/Fix Color Test. In HBD#1328, Dr. Fix describes a test based on diluting a dark beer of known color until it matches the beer being tested. He suggests the use of Michelob Classic Dark (color = SRM 17) as a standard since it is cheap and readily available in the US. In the article he provides a crude ASCII calibration chart; in response to an email query he kindly provided the original data used to generate the chart. This data is given below; I recommend you replot for better accuracy than ASCII graphics allow. Each data line shows the amount of water added to a 20 ml sample of Michelob Classic Dark to match a beer of known color.
SRM Dilution (ml) Sample 17 0 Michelob Dark 13 20 Noche Bueno 10 35 Bass 9 50 Anchor Steam 7 70 Ottobeurer Fest 5 100 EKU 4 115 Molson Export 3 160 Miller 2.5 200 Coors 2 260 BudI recommend you read the original article for details on carrying out the test, but basically you dilute a 20 ml sample of Michelob Classic Dark until the color matches that of your beer. Based on the amount of dilution needed, you then read the SRM color of your beer off the calibration curve.
Dr. Fix has heard a rumor that Michelob Classic Dark is being discontinued. If this happens, a new calibration curve will be needed. Another problem is that this scale stops at 17 SRM; all of my stouts are off-scale.
3. Prepared standards. I didn't want to have to keep a stock of schlock beer on hand for testing, so I made up a set of reusable samples based on Dr. Fix's data. I was able to get a good empirical fit of the data to a cubic equation:
% classic dark = -4.33 + 6.86(SRM) - 0.689(SRM)^2 + 0.0380(SRM)^3
Using this equation, you can calculate a composition to generate a sample of any SRM color below 17:
SRM % classic dark 2 6.9 3 11.1 4 14.5 5 17.5 6 20.2 7 22.9 8 25.9 9 29.2 10 33.3 11 38.3 12 44.3 13 51.8 14 60.8 15 71.6 16 84.5 17 100.0After dilution, I sealed my samples in ampules and heated them 10 minutes in a boiling water bath to pasteurize. No obvious color change was noted upon heating, but in retrospect it would have been better to use cooled, pre-boiled water for dilution and seal in sanitized ampules.
Q: Any advice on performing comparisons?
A: Many factors influence perceived beer color, and you must control them to get good test results.
1. turbidity and bubbles make beer appear lighter. Measure the beer after the yeast has sedimented, do it at room temperature to avoid chill haze, and let it go flat to avoid bubbles. You can degas beer nicely by spinning it in a blender, then allowing the foam to decay.
2. The color looks deeper if you look through more beer. (Through an ironic coincidence, chemists quantify this effect with an equation called "Beer's Law"). Your standard and the beer being tested must be in identical containers filled to identical depths. In the case of printed or film standards, you must use the same container and depth as the person who generated the standard.
3. The backdrop matters. I set my samples on a piece of white paper to give a consistant, neutral background.
4. Ambient light matters. You want uniform, fairly bright white light. If the light is too dim, everything looks the same.