Standard Reference Method
Beer colourexact by definition
The Standard Reference Method measures beer colour as absorbance of 430 nm light through a 1 cm path, multiplied by 12.7. It is the North American brewing scale: a pale lager sits near 2–4 SRM, an amber ale near 10–14, a porter near 30, and anything past about 40 is opaque black.
Watch out: SRM measures absorbance at a single wavelength, so it records how DARK a beer is and not what hue it is. Two beers at the same SRM can be visibly different colours, which is why the scale is paired with a description rather than used alone.
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SRM was adopted by the American Society of Brewing Chemists in 1950 to replace degrees Lovibond, which depended on a brewer comparing a sample against coloured glass discs by eye and therefore on the brewer's eyes.
About the standard reference method
Beer colour is measured, not judged, and the measurement is a straightforward spectrophotometry: shine 430 nm light through a 1 cm sample and record how much is absorbed. SRM is that absorbance times 12.7.
The conversion to the European scale is exact and worth carrying: EBC = 1.97 × SRM, so a 10 SRM amber is 19.7 EBC. The factor exists because EBC uses the same absorbance with a different multiplier, nothing more.
Degrees Lovibond is the odd one out and cannot be converted with a factor. It is a visual scale, and its relationship to SRM is an empirical fit — the usual approximation is . Malt is still sold in degrees Lovibond while finished beer is measured in SRM, so a recipe calculation crosses between them exactly once, at the point where grain colour becomes wort colour.
The practical limit of all of this is that colour prediction is much worse than colour measurement. Morey's equation and its rivals fit observed data reasonably below about 20 SRM and diverge badly above it, because absorbance stops being linear in malt loading once the wort is dark. A predicted 45 SRM stout means "black", and no more than that.
One standard reference method in every beer colour unit
| 1 | Standard Reference Method (SRM)this unit | |
| 1.97 | European Brewery Convention (EBC) |