Beer colour (SRM) — Morey formula
Estimate the colour (SRM) of finished beer from the grain bill and batch volume.
Formula
MCU per grain = (Lovibond × weight_lb) ÷ batch_gal Total MCU = sum of all MCUs SRM = 1.4922 × (Total MCU ^ 0.6859)
Inputs
| Name | Unit | Description |
|---|---|---|
| L | lovibond | Lovibond colour rating of each grain (1 Lovibond ≈ 1.97 EBC) |
| W | lb | Weight of each grain (US pounds; 1 kg = 2.205 lb) |
| V | US gal | Post-boil batch volume |
Outputs
| Name | Unit | Description |
|---|---|---|
| SRM | - | Standard Reference Method colour. EBC = SRM × 1.97. |
Worked example
Inputs:
- maris_otter_lb = 11.9
- maris_otter_L = 3
- crystal_60_lb = 0.9
- crystal_60_L = 60
- batch_gal = 5
Calculation:
MCU(Maris Otter) = 3 × 11.9 ÷ 5 = 7.14 MCU(Crystal 60) = 60 × 0.9 ÷ 5 = 10.8 Total MCU = 17.94 SRM = 1.4922 × 17.94^0.6859 = 1.4922 × 6.93 = 10.3
Result:
~10 SRM (a deep gold to amber colour)
Sample values
| Beer style | Typical SRM | EBC equivalent |
|---|---|---|
| Pilsner | 3 | 6 |
| Hefeweizen | 4 | 8 |
| Pale ale | 7 | 14 |
| Amber ale | 12 | 24 |
| Porter | 30 | 59 |
| Stout | 40 | 79 |
Why Morey
Morey’s empirical formula is the most widely-used SRM predictor in homebrew software. It outperforms the simpler MCU-only equation across the full colour range. For very dark beers (SRM > 40) all predictors converge into “essentially black”, so the formula’s accuracy doesn’t matter visually.
Limits and caveats
- Grain colour is rated post-malting, not as-mashed. Long boils darken the wort further by Maillard reactions; a 90-minute boil adds ~1-2 SRM beyond the formula’s prediction.
- Decoction mashing drives more Maillard browning than infusion. A decoction-mashed Bohemian Pilsner sits at the deeper end of the style’s colour range.
- Roast malts dominate. Anything above 300 °L (chocolate, black, roast barley) contributes disproportionately to colour; small weight changes in roast malts visibly shift the finished beer.
When you’ll be wrong
If you brew the same recipe twice and your colour predictions are off by 2-3 SRM, that’s within expected error. If you’re 10 SRM off, check whether your grain bill was milled and weighed correctly.