proposed FAQ on measuring color
Dave Whitman
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 dwhi...@rohmhaas.com.
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 + 0.45
Unfortunately 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 (dwhi...@rohmhaas.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 76
Depending 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
ddav...@earth.execpc.com 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 Bud
I 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
17 100.0
After 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.
-----------------------------------------------------------------
* "The opinions expressed are those of the
Dave Whitman * writer and not Rohm and Haas Company."
dwhi...@rohmhaas.com * They made me say that. Honest.
Alan Marshall
<dwhi...@rohmhaas.com> writes:
<FAQ snipped for the sake of bandwidth.>
Excellent start. This will be of interest to David Draper and Pat
Steppic as well. The later is studying photographic imaging at RIT
and has thought of beer colour measurement as a major paper topic.
Regarding Dr. Fix's dilution solution (isn't this alt.poetry?): Dave
notes that the Michelob Dark base is limited because it stops at SRM
17. Why not have someone competent (i.e., not me) do a colour
gradient(s) based on an extremely dark beer. Both Guinness Pub Draft
in cans (only moderately "black") and Sam Smith's Oatmeal Stout are
widely available. Colour gradients based on these beers would be more
useful than the current MD based gradient.
BTW in the Beer Records FAQ that I maintain and post monthly to alt.
beer and r.f.d.b, the darkest beer entry reads:
BR> Darkest Beer:
BR>
BR> The darkest beer I have been able to find is Farson's Lacto Milk
BR> Stout (Malta) at 450 EBC (57+ SRM). (MJBC p 188) By comparison,
BR> Guinness Draught is 130 EBC, and Mackeson's ranges from 225 EBC,
BR> for the U.K. version, to 300 EBC for the export version.
It would seem that the "ultimate" gradient would be based on FLMS.
BTW, if anyone knows of a darker beer, or a commercial beer in excess
of 100 IBU (Alimony Ale and Thomas Hardy's are both about 100 IBU),
please let me know so I can update the FAQ.
--
-- Alan Marshall "That's, as they say, a chunk of
AK20...@SOL.YORKU.CA change," Binger in the WSJ
York University
Toronto, Canada