Recipe

This is the guide for a recipe builder, a brew-day sheet, or anything else that holds a whole recipe and wants all its numbers at once. It also covers the gravity readings you take along the way.

The functions to start with

• calculateRecipe answers "what will this recipe make?" It returns the vitals, the volume waterfall, each fermentable's and each hop's share, the strike temperature and, when the recipe has them, the water chemistry and the decoction plan.
• recipeChecks answers "is there anything I should know before brew day?" It reads what calculateRecipe returned and reports problems in the order you'd hit them on the day: kettle, mash, fermenter, pH, pitch, fermentation temperature, style.
• correctHydrometerReading, refractometerFinalGravityRaw and abv answer the questions you have once it's brewing: what a warm sample really reads, what a refractometer reading means once there's alcohol in it, and how strong the beer came out.

A recipe on a small kettle

Start here ran the README's pale ale on the default equipment. Here it is on a 25 L kettle with a 23 L fermenter:

const equipment: EquipmentProfileInput = {
  name: '25 L kettle',
  kettleVolumeL: 25,
  fermenterVolumeL: 23,
};

const calculation = calculateRecipe(paleAle, equipment);
const { findings, supersedes } = recipeChecks({ recipe: paleAle, equipment, calculation });

const summary = findings.map((finding) => `${finding.severity}: ${finding.id}`);
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The pale ale needs 25.2 L in the kettle when the boil starts, so findings has two entries:

• a warning with id boil-over-kettle, saying the boil overflows the kettle by 0.19 L;
• a note with id fermenter-headspace. 20 L in a 23 L fermenter leaves 3 L of headspace, and the check would like a quarter of the fermenter, 5.75 L.

Each finding is a typed object with its numbers on it, discriminated on id, so you write the sentence yourself in whatever words and units your app uses. calculateRecipe also put "Pre-boil volume 25.2 L exceeds the kettle's 25 L." in its own warnings. supersedes returns that exact string, so if you show both lists you can drop the duplicate.

Two of the checks need something extra. The pitch check needs now, the date to judge the yeast's age against, because a function that read the clock would give different answers on different days. The style check needs styleBands, the OG, FG, IBU and SRM ranges of the style you're aiming at. Leave either out and that check is skipped.

The working, and choosing formulas

result.explain has an Explanation for each headline number. For the pale ale, explain.og says the formula is extract-bookkeeping, shows the expression, and lists its inputs: 21.3 L post-boil, 75 % mash efficiency, 1,081.9 point-liters of extract out of a theoretical 1,442.5. Its source is Palmer's How to Brew.

CalculationOptions picks the formula where there's a choice. The same recipe under Rager instead of Tinseth:

const tinseth = calculation.vitals.ibu;
const rager = calculateRecipe(paleAle, equipment, { ibuFormula: 'rager' }).vitals.ibu;
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Tinseth gives 33.0 IBU and Rager 37.7. The two are fits to different data and a gap that size is normal between them, which is why the explanation always says which one ran.

Readings on brew day

A hydrometer sample at 32 °C that reads 1.048, and refractometer readings of 12.4 °Bx before pitching and 6.6 °Bx at the end:

// The hydrometer read 1.048 in a sample still at 32 °C.
const og = correctHydrometerReading(1.048, 32);

// The refractometer read 12.4 °Bx before pitching and 6.6 °Bx at the end.
const fg = refractometerFinalGravityRaw(12.4, 6.6);

const strength = abv(og, fg);
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The warm sample is really 1.052. The refractometer's final reading works out to 1.011, and the beer is 5.5 % ABV.

Traps

• The batch size is into the fermenter. batchVolumeL means chilled wort going into the fermenter unless you set batchVolumeBasis: 'packaged'. Everything upstream (strike, sparge, pre-boil) is worked back from it.
• Hops are in kilograms. A 28 g addition is amountKg: 0.028. It's the most common mistake, and the IBU comes out a thousand times too high.
• Give a malt's yield one way. A fermentable takes either extractFineGrindDryBasisPercent (the maltster's figure) or ppg. If you pass both, ppg wins, on the reasoning that it's the number someone typed in to override the catalog.
• A refractometer reading needs both readings once fermentation starts. refractometerToGravity is for unfermented wort only. Once there's alcohol, use refractometerFinalGravityRaw with the original and the current reading. It applies the wort correction factor (1.04 by default) to both, so pass what the instrument shows.
• ABV comes from the OG-equivalent. If the recipe adds sugar in the fermenter, vitals.og is what a hydrometer reads on the wort and vitals.ogEquivalent includes the sugar. ABV uses the second.

Going further

• Gravity, IBU and color has the formulas behind the vitals.
• Volume corrections explains the volume waterfall.
• Refractometer and hydrometer covers the reading corrections.
• In the reference, the Recipe and Gravity and ABV categories list the rest: planVolumes for the waterfall alone, predictGravities for gravity without the rest of the recipe, and the inputs such as RecipeInput and EquipmentProfileInput.