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Standard Reference Method or SRM is a system modern brewers use to measure color intensity, roughly darkness, of a beer or malted grain. This method involves the use of spectrophotometry to assign a number of degrees SRM to light intensity.

The SRM number is defined as 10 times the absorbance of a sample at 430 nanometers measured through a .5-inch cell. The 430-nanometer wavelength corresponds to a deep blue light, and is the wavelength at which beers appear most different from each other.

The standard was adopted in 1950 by the American Society of Brewing Chemists as an objective measurement of color unburdened by the difficulties of the Lovibond system; the measurement of the color of a beer in degrees SRM and degrees Lovibond are approximately equal and in practice can be used interchangeably to evaluate the color of intensity of beer.

Degrees SRM are related to the current EBC standard by:

$\mbox{EBC} = \mbox{SRM} \times 1.97$
$\mbox{SRM} = \mbox{EBC} \times .508$;

as a rule of thumb, EBC is approximately twice SRM.

Note that an earlier version of EBC color was based on absorbance at 530 nanometers, which permitted no direct conversion between the two systems. However, if one assumes a linear log absorbance spectrum (the Linner hypothesis from the realm of caramel color), and knows the Linner Hue Index, $H_L$, the absorbances are related by:

$A_{430} = A_{530} \times 10^{H_{L}/10}$

A formula for converting between the old EBC color value and SRM sometimes continues to appear in literature. It should not be used, as it is flawed and based on measurements which are no longer taken.

## Color based on Standard Reference Method (SRM)Edit

SRM/Lovibond Example Beer color EBC
2 Pale lager 4
3 German Pilsener 6
4 Pilsner Urquell 8
6 12
8 Weissbier 16
10 Bass pale ale 20
13 26
17 Dark lager 33
20 39
24 47
29 Porter 57
35 Stout 69
40 79
70 Imperial stout 138

## ReferencesEdit

 This page uses content from Wikipedia. The original article was at Standard Reference Method. The list of authors can be seen in the page history. As with Beer Wiki, the text of Wikipedia is available under the Creative Commons Attribution-Share Alike License 3.0.