Calculating SRM
The original scale to measure beer color is called degrees Lovibond (°L) and was created by Joseph Williams Lovibond (1885). With the invention of the spectrophotometer a new system was created, the Standard Reference Method (SRM) and European Brewing Convention (EBC). Lighter values have a lower SRM number and darker values have a higher SRM number. SRM values over 50 are considered black.
Based on the Lovibond number of your malt you are able to estimate the color of your finished beer. Remember Lovibond is used to measure the malt color and SRM is used for the final color for the beer. First we determine the Malt Color Units (MCU). Malt Color Units (MCU) is the color of each grain times the grain weight in pounds divided by the batch volume in gallons. When more than one fermentable is used, the MCU color is calculated for each fermentable and then added together.
MCU = (Grain Weight lbs. * Grain Color deg L) / Volume gal
Calculating MCU, alone, provides a fair color estimate for beers that are very pale in color but, because light absorbance is logarithmic and not linear, we need to use the Morey equation for a better estimate of color for most beers:
SRM Color = 1.4922 * (MCU ^ 0.6859)
Calculating SRM from a Mash Grain Bill - 5 gal Batch Example
Step 1: Calculate Malt Color Units (MCU)
9.0 lb. Maris Otter (4° Lovibond)
1.0 lb. Crystal 77L (77° Lovibond)
(9.0 lb. x 4°L) / 5 gal = 7.2 MCU
(1.0 lb. x 77°L) / 5 gal = 15.4 MCU
Total = 22.6 MCU
Step 2: Apply the Morey Equation
SRM Color = 1.4922 * (22.6 MCU ^ 0.6859) = 12.7 SRM
For the estimated color of the finished beer, find 12 or 13 on the SRM Color Chart below.
SRM Color Chart
