Brewing & Fermentation formulas — 13 solvers

Alcohol by Volume from Gravity

ABV = (OG - FG) \times 131.25

Brewing & FermentationThe standard homebrew estimate of alcohol by volume from the original and final gravity readings — the single most-used calculation in brewing, and one of the least exact.

Apparent Attenuation

AA = \frac{OG - FG}{OG - 1}

Brewing & FermentationThe share of the wort's original extract that the yeast has fermented away, read off the hydrometer. The number that says whether a fermentation has finished or has stalled.

Beer Colour (Morey's Equation)

SRM = 1.4922 \times MCU^{0.6859}

Brewing & FermentationTurns malt colour units into a predicted beer colour on the SRM scale. Morey's power law is the correlation most recipe software uses, and it exists because colour does not add up linearly.

Brewhouse Efficiency

E = \frac{m_a}{m_p}

Brewing & FermentationThe share of the extract locked in the grain that actually reached the kettle. The definitional form — extract recovered over extract available — from which every working efficiency figure descends.

Dilution to a Target Gravity

V_2 = \frac{V_1 P_1}{P_2}

Brewing & FermentationThe volume a wort reaches once it is diluted to a lower gravity, worked in gravity points. The fix for a batch that came out stronger than the recipe asked for.

Gravity Points from a Grain Bill

P = \frac{PPG \times W \times E}{V}

Brewing & FermentationThe gravity a grain bill should produce, from each malt's potential, the weight used, the brewhouse efficiency and the batch volume. The forecast every recipe is built on.

Hop Utilisation (Tinseth)

U = \frac{1.65 \times 0.000125^{\,G_b - 1}\left(1 - e^{-0.04\,t}\right)}{4.15}

Brewing & FermentationThe fraction of a hop addition's alpha acids that actually isomerise into the beer, as a function of boil gravity and boil time. Glenn Tinseth's 1997 correlation, still the industry default.

IBU from Utilisation

IBU = \frac{U \times m_\alpha}{V}

Brewing & FermentationThe bitterness a hop addition delivers: the mass of alpha acids that isomerised, divided by the volume it ended up in. One IBU is one milligram of iso-alpha acid per litre.

Infusion Volume for a Mash Step

W = \frac{(T_2 - T_1)\,(0.2\,G + W_m)}{T_w - T_2}

Brewing & FermentationHow much hot water to add to a mash already sitting at one temperature to bring it to the next rest. The heat balance behind every step-mash schedule.

Malt Colour Units

MCU = \frac{L \times W}{V}

Brewing & FermentationThe colour a grain bill contributes, weighted by how much of it there is and how far it is diluted — the raw input to every beer-colour correlation.

Mash Strike Water Temperature

T_w = \frac{0.2}{R}\,(T_2 - T_1) + T_2

Brewing & FermentationHow hot the water must be so that grain at room temperature and water together settle at the mash temperature you want. Palmer's form, from a heat balance between grain and water.

Priming Sugar for a Carbonation Level

m = \frac{1.9635 \, V \,(C_t - C_r)}{y}

Brewing & FermentationHow much sugar to add at packaging so the yeast produces exactly the carbonation you want, allowing for the CO₂ the beer already holds and for what the sugar actually yields.

Specific Gravity to Degrees Plato

P = 259 - \frac{259}{SG}

Brewing & FermentationConverts a hydrometer's specific gravity to degrees Plato, the percent of dissolved extract by weight that a refractometer and every commercial brewery report.