How does the optimizer balance OG and colour?

It sweeps the specialty malt's share of the bill from 0 to 100 percent. For each ratio it computes the total grain weight needed to hit OG, then the resulting SRM colour. It keeps the ratio whose combined squared error against both targets is lowest.

How is beer colour calculated?

It uses Malt Colour Units (MCU), which is the sum over all grains of (grain colour in Lovibond × pounds) divided by batch volume in gallons. MCU is then converted to SRM with the Morey equation: SRM = 1.4922 × MCU raised to the power 0.6859.

What extract potential should I enter?

Extract potential is the gravity points per pound per gallon (PPG) a malt yields at 100 percent efficiency. Typical values are about 37 for two-row base malt, 34 to 35 for crystal malts, and 33 for roasted malts. Your brewhouse efficiency scales this down.

Why might no combination hit both targets exactly?

Two malts give only one degree of freedom for two goals. If your base malt is pale and your specialty malt is very dark, some OG and SRM pairs are simply unreachable with that pair. The tool shows the closest possible result and the residual error.

Does this account for boil-off or late additions?

It works at the level of finished-volume original gravity, so enter the batch volume into the fermenter. Boil-off concentration is already captured by using post-boil volume and your measured brewhouse efficiency.

What is the Grain Bill Color & OG Optimizer?

Balances base malt and specialty malt proportions to reach an original gravity target and an SRM colour target at the same time. Iterates over grain ratios using MCU and the Morey equation to display the closest achievable two-malt combination. It runs free in your browser on Gera Tools, with nothing uploaded.

Grain Bill Color & OG Optimizer

Name: Grain Bill Color & OG Optimizer
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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This optimizer solves a common homebrew problem: you want a beer at a specific original gravity and a specific colour, using just a base malt and one specialty malt. It sweeps every grain ratio and reports the two-malt bill that gets closest to both targets at once.

How it works

There are two equations in play.

Gravity. A malt’s contribution in gravity points is:

points = PPG × weight(lb) × efficiency / volume(gal)

Summed over the bill, the points give OG as 1 + points/1000. The tool inverts this to find the total grain weight needed for your OG at each ratio.

Colour. Beer colour starts as Malt Colour Units:

MCU = Σ (grain Lovibond × grain lb) / volume(gal)

MCU is then converted to SRM with the widely used Morey equation:

SRM = 1.4922 × MCU^0.6859

Because two malts give only one free ratio but you have two targets, the tool minimises the combined error: it scans the specialty malt’s share from 0 to 100 percent, computes OG and SRM at each step, and keeps the ratio with the smallest squared distance from both targets.

Worked example

Target OG 1.050, target SRM 12, in a 20L batch at 72 percent efficiency, using a 3°L base malt (37 PPG) and a 60°L crystal malt (34 PPG). The optimizer finds a bill that is mostly base malt with a modest crystal addition, lands OG very near 1.050, and pushes SRM toward 12 from the crystal’s colour. If the crystal is too light to reach SRM 12 at a reasonable share, the tool reports the closest SRM it can achieve and flags the residual.

Tips and notes

For darker targets, choose a darker specialty malt (e.g. chocolate or roasted barley at 300 to 500°L) so a small percentage moves the colour a long way.
SRM rises faster than linearly at low MCU and slower at high MCU — that is the Morey curve, and it is why pale beers are sensitive to tiny crystal additions.
The optimizer assumes both malts share the same efficiency; in practice highly kilned grains convert slightly less, so treat the bill as a starting recipe and adjust after your first brew.