The Morey Model for Malt Chromaticity
Standard Reference Method (SRM) is the analytical scale used to define beer color. While the scale is linear (SRM 40 is twice as dark as SRM 20), the way light travels through a sugary liquid is not. To accurately predict the color of a beer based on its grain bill, brewers use the Morey Equation, which applies a power-law correction to the simpler Malt Color Unit (MCU) calculation.
Malt Color Units (MCU) vs. SRM
MCU is the basic starting point: (Weight of Grain * Lovibond) / Volume.
- For very light beers (under 10 SRM), MCU and SRM are nearly identical.
- For dark beers, the MCU drastically overestimates the color because the liquid becomes so dense that light absorption becomes logarithmic. The Morey Equation corrects for this 'darkness bias.'
The Formula
First, calculate the MCU for every grain in the bill, then apply the Morey exponential constant.
Where:
SRM=
The final predicted color valueMCU=
Total Malt Color Units [(Weight * Lovibond) / Volume]1.4922 / 0.6859=
Constants derived from Dan Morey's statistical analysis of beer samplesLovibond (°L) and EBC
- Lovibond: The historical scale used for the color of raw malt.
- EBC (European Brewing Convention): The color scale used in Europe. EBC is approximately SRM * 1.97. The color of your final beer is also influenced by the 'boil-off' rate (caramelization of sugars) and the clarity of the beer (turbid beers look lighter than bright beers).