Your batch and process
These set the original gravity and bitterness everything scales from.
Grain, extract and sugar
Set each row's type — efficiency applies to mashed grain, while extract and sugar count at 100%. The gravity toggle marks what moves when you scale by gravity: leave it on for base malt, extract and sugars; turn it off for specialty malts you want held at the same weight. Color is in degrees Lovibond and drives the recipe's estimated SRM. Type a known ingredient name to autofill yield, type and color from the built-in database.
Base and kilned malts swap to (or from) malt extract at the same gravity, solved against your mash efficiency. Pale malts route to pale extract, wheat to wheat, and Munich-type malts (Munich, dunkel, melanoidin, or any kilned base malt around Munich colour and up) to Munich extract — so the colour holds far better. Specialty steeping grains and sugars are left untouched.
The bittering and aroma schedule
Set each addition's use — boil additions take a time in minutes from the end of the boil; whirlpool and hop-stand additions take a temperature and a stand time and are modeled with continued cooldown isomerization. Type a hop name to autofill a typical alpha-acid figure — always overwrite it with the number from your actual package, since alpha swings hard by crop year. IBUs are computed at the boil gravity the scaled recipe actually reaches.
Tinseth — the modern default; gentler utilization, gravity baked into every addition. Match whatever your other software uses so the IBU numbers mean the same thing to you.
Immersion — a moderate cool; whirlpool and flameout hops keep isomerizing as the wort falls past ~80, 70, 60°C. Only affects whirlpool, hop-stand and flameout additions.
Finings, salts, nutrients, yeast
These scale straight with batch volume. They're held unchanged when you scale by gravity, efficiency or boil — the batch size isn't changing in those modes.
Pick a lever
One lever at a time. The others stay at what you brewed, so you always see a clean before-and-after.
Everything multiplies by the same ratio. Gravity and bitterness ride along untouched.
Re-weight hops so the bitterness-to-gravity ratio stays where you brewed it — a session version stays balanced, an imperial gets the bitterness it needs.
The scaled recipe
Fermentables
Hops
Other additions
How the scaling works
Gravity is summed in points: points = weight(lb) × yield(PPG) × factor ÷ volume(gal), where the factor is your mash efficiency for grain and 100% for extract and sugar. Sum across fermentables and you have OG.
Volume multiplies every ingredient by one ratio — gravity holds, so utilization holds, so IBUs come along for free. Gravity holds the specialty (gravity-toggle off) fermentables at weight, subtracts their points from your target, and solves the remainder from the base malt. Efficiency is the same solve, triggered by a change in the efficiency factor. Boil-off treats time and rate as one lever (their product is the wort lost) and lets you choose what gives: hold the grain bill and pre-boil volume and let the batch shrink and concentrate; or hold the finished beer and solve the pre-boil volume to collect; or give pre-boil and target volumes and solve the boil time needed.
Bitterness uses your chosen formula — Tinseth or Rager. When gravity moves, utilization shifts, so hops are re-weighted to hold your BU:GU ratio by default — or absolute IBU, or left alone — your call above. Boil gravity is taken as the average of pre- and post-boil, shown in the process strip so you can check it against your own numbers. Boil and first-wort additions use the timed-boil math; whirlpool, hop-stand and flameout additions use an mIBU-style model built on measured kinetics: once the flame is out, isomerization keeps running but at a temperature-scaled rate taken from Malowicki & Shellhammer (2005), Urel(T) = e^(−11858·(1/T − 1/373.15)) with T in kelvin — about 1.0 at boiling, 0.50 at 92°C, 0.17 at 80°C, 0.06 at 70°C. Each minute of the hold and of the kettle's cool-down is weighted by that factor and folded back into the Tinseth curve, so the cooling speed you choose (counterflow, immersion, or no-chill) sets how much late bitterness lands. Post-boil additions are modeled on the Tinseth temperature curve even in Rager mode, since Rager has no late-hop model.
Colour is the Morey estimate: MCU = Σ(°L × lb) ÷ gal, then SRM = 1.4922 × MCU^0.6859 (EBC ≈ SRM × 1.97). Because volume scaling moves every grain together, colour holds — but in gravity mode the base grows while specialty stays put, and in boil-off the batch concentrates, so the swatch shifts to show it. The autofill database is the same verified malt-and-extract dataset that powers the substitution finder — base, specialty and brand-named malts plus LME/DME extracts — alongside generic category fallbacks and sugars; alpha acids are typical figures to override from your package.
Format conversion holds gravity rather than weight. Going to extract, each base or kilned grain's effective points — weight × PPG × efficiency — are delivered by an extract at 100%, so the extract weight is grain points ÷ extract PPG (LME ≈ 36, DME ≈ 44). Going back to grain reverses it: extract points ÷ (grain PPG × efficiency). Each grain is routed to a like extract — pale to pale, wheat to wheat, and Munich-type malts (by name, or any kilned base malt from ~Munich colour upward) to Munich extract — so colour is largely held rather than washed pale. Specialty steeping grains and sugars count the same either way and are left untouched.
Pitching rate and water salts scale with both volume and gravity, but they're their own craft — take the scaled OG and batch size here over to the Pitch Rate and Water Adjustment tools rather than trusting a single multiplier.
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