Playing the Percentages

BYOB by | Oct 2015 | Issue #105
Illustration by Ellen Crenshaw

My next book involves recipes by a number of solid homebrewers and it made me realize just how personal written recipes are. Anybody can glean the relevant data from most formats. But one of them is decidedly different—the percentage format used by professionals.

Basically, it’s an attempt to divorce recipe amounts from purely physical measures. Instead of pounds and kilos, grain is expressed as a percentage of the total grain bill. Combined with the target gravity you can use a little razzle-dazzle math to re-create a recipe that’s theoretically independent of system efficiency and volume. What follows is a simplified methodology for homebrewers. To demonstrate, I’ve listed this month’s recipe, Calculator Cream Ale, in percentages.

Start with your system’s efficiency—say 75 percent. Multiply it into an average malt gravity contribution of 36 points per pound to get 27 points per pound, the gravity your system yields from a pound of grain (36 x 0.75 = 27).

Next, take the target gravity points (50) and multiply them by the desired volume (5 gallons) for 250 points (5 x 50 = 250). Then divide your points by your yield (250 / 27) to get the total malt weight needed: 9.26 pounds.

From there, it’s easy. Multiply the total malt weight by each percentage value to determine the amount needed for each grain. In this case, 90 percent Pilsner and 10 percent flaked maize means 8.3 pounds and 15 ounces respectively. For hops, I depend on calculator software to figure out I need 0.25 ounces of Magnum and 0.50 ounces of Mt. Hood for my batch.

CALCULATOR CREAM ALE
For 5.0 gallons at 1.050,  3 SRM, 17.5 IBU, 5.2% ABV

Grain
90% domestic Pilsner malt
10% flaked maize

Mash
Strike at 152°F for 60 minutes.

Hops
15 IBU Magnum | 60 minutes
2.5 IBU Mt. Hood | 10 minutes

Yeast
WLP001 California Ale Yeast, Safale US-05, Wyeast 1056 American Ale or WLP080 Cream Ale Blend

Notes
Ferment for two weeks at 58–64°F. Crash and lager at 32°F for two additional weeks.