Question: "Beer Fox, I have been reading about beer styles and would like to know what SRM numbers are. Can you help?" J.C., Arvada, Colorado, USA
Answer: SRM is the abbreviation for Standard Reference Method, a scale used to classify the color of beer in the USA. It is based on degrees Lovibond (degL). Calibrations between the SRM scale and degL scale are similar.
Commercial breweries measure this color using a spectrophotometer, a sophisticated device that provides an accurate machine measurement of the quantity of monochromatic light, either absorbed, or passing through, the liquid. This instrument produces data that describes the color of the sample product, ranging from the almost colorless (2-3) American light lagers to the almost black (30-40+) stouts and porters.
Homebrewers do not have the advantage of such expensive equipment. However, as an aide to fellow brewers, the State of Franklin Homebrewers has provided a color chart for your convenience.
A few things to keep in mind when evaluating a beer for color:
View beer in a white room – White walls, white tablecloth, through a clear, colorless glass.
Use uniform, bright light when viewing.
Color appears denser if you look through more beer. When comparing beer color, always look through a glass that is the same for each beer.
Turbidity and bubbles cause a beer to appear lighter than it is.
Measure at room temperature to avoid chill haze.
Numbers on the SRM scale are not linear. A beer that has an SRM of 20 is not two times darker than a beer with a measurement of 10.