The Six Numbers in Every Recipe

A recipe is six numbers. Working them out in the right order, before brew day, is most of what separates a batch that lands where you intended from one that merely turns out.

One: volume

Everything else is a concentration, so the batch volume is the denominator of the whole recipe. Decide the post-boil volume you are actually going to collect — not the nominal size of your kettle — and use it consistently.

Missing this by two litres in twenty changes gravity, bitterness and colour by 10% each, all in the same direction, which is why an otherwise careful brewer's batches drift.

Two: gravity

The grain bill sets the original gravity, and the OG together with your yeast's expected attenuation sets the finishing gravity and the strength. Run the pair through the ABV calculator to see where you will land: 1.050 to 1.010 is 5.25% at 80% attenuation.

Deciding the FG in advance rather than discovering it is what lets you judge, weeks later, whether the fermentation actually did what it should have.

Three: colour

Build the grist for flavour, then check it with the SRM calculator. Because dark malts are extraordinarily concentrated — 300 g of roast in a 5 kg grist takes a beer from gold to nearly black — colour is adjusted in tens of grams at the end rather than designed from the start.

Four: bitterness

The IBU calculator needs the boil gravity, not just the original gravity, and it is sensitive to it: the same hops give 30% fewer IBUs at 1.080 than at 1.040.

Judge the result against the gravity rather than in isolation. The same 30 IBUs reads as bracing in a dry lager and as balanced in a malty amber, which is why style guidelines always quote the two together.

Five: mash temperature

This sets fermentability, and therefore the finishing gravity you assumed in step two. Lower mashes give a drier beer, higher ones a fuller body — roughly 63, 66 and 70 °C for dry, balanced and full.

The strike water calculator turns that into a temperature to heat the water to, given your grain weight, its temperature and your water-to-grain ratio. Do it the night before; it is the one number you need at a moment when the kettle is already hot.

Six: carbonation

Chosen at design time even though it is applied at the end, because it belongs to the style: 1.5–2.0 volumes for British ales, 2.2–2.6 for most American ales and lagers, 3.0 and up for wheat beers and Belgians.

The priming calculator needs the beer's warmest post-fermentation temperature, and anything above about 3 volumes needs bottles rated for it.

Write down what actually happened

The planned figures and the achieved ones, side by side: volume collected, OG, FG, mash temperature hit, strike temperature used. Three batches of that and you know your own system's efficiency and its heat losses, which no calculator can tell you.

That record is worth more than any recipe. It is the difference between brewing a beer again and brewing something like it.