What is the Standard Reference Method (SRM)?

The Standard Reference Method (SRM) is a method for color assessment of wort recommended by the American Society of Brewing Chemists (ASBC). The SRM of a sample is measured in a cell path length of 1cm with 430nm wavelength light. The absorbance level measured is then multiplied by a factor of 12.7 to yield the color value assigned to the sample of wort. Typical SRM values are between 1 and 40, with 1 being described as ‘pale straw’ and 40 being ‘dark black.’ SRM values can exceed 40 but the assessment becomes less accurate with darker samples. A dilution technique can be applied for these darker wort samples, in which the sample is diluted, and the taken measurement is scaled up to match an undiluted value.