Standard Reference Method

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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 EBC standard by:

;

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

[edit] Color based on Standard Reference Method (SRM)

SRM	Typical beer	Typical color
2.0	Budweiser
3.0	German Pils	Yellow/straw/gold
4.2	Pilsner Urquell
10	Bass Pale Ale	Amber
17	Michelob Dark	Brown
35	Stout	Black
70	Imperial Stout	Opaque black