Beer Math

On this page, we will be placing all of our practical "beer math" knowledge. Of course, one can make endless calculations using a whole host of beer variables. However, here you will find the most practical that we use in our homebrew calculations.

Calculating Percent Alcohol and Calorie Content

These calculations will eventually find there way into a separate page in the form of a little online calculator (i.e., you enter the values, and we'll spit back the answer): These calculations were taken from Michael L. Hall's article Brew by the Numbers: Add Up What's in Your Beer (Zymurgy, Summer 1995, vol. 18, no. 2).

Calculating Mass of Priming Sugar

The amount of priming sugar to add is generally stated at 3/4 cup per 5 gallons of brew. Since we want to arrive at a certain mass of CO2, we would need to know the density of the priming sugar to determine its mass. Since density estimates of priming sugar varies, we are better off measuring by mass. So, use this equation which will yield the mass of needed priming sugar in grams:

PS (grams) = 15.195 Vb ( CD - 3.0378 + .050062 * T - .00026555 * T * T );

where Vb is volume of beer in gallons, CD is carbon dioxide concentration in the final brew in volumes, and T is temperature at bottling.

Desired value of CD is 2.2 to 2.6 for most beers, 1.8 to 2.2 for British ales, 2.5 for lagers and German ales, 2.6 to 2.8 for American beers, and 3.0 for wheat beers and fruit ales.

To plug and play, go to this Online Carbonation Calculator.

This calculation was also taken from Michael L. Hall's article Brew by the Numbers: Add Up What's in Your Beer (Zymurgy, Summer 1995, vol. 18, no. 2).

Predicting Original Gravity Using Extract and Specialty Grains

To help build recipes that target specific gravities, you can use this formula:

OG in points = (Points) * (lbs of malt used) / (gallons of beer brewed)

for each ingredient that adds to the density of the wort. For malt extracts, "Points" = 35 for syrup (in practice it's about 30) and 42 for dried extract. For speciality grain contributions, Pale Malts = 29 points, vienna/munich/amber = 25, wheat = 26, cara pils = 20, crystal = 8, black = 2.

To get a result in the traditional 1.xxx form, divide your OG "points" result by 1000 and add 1. So, 40 would become 1.040.

For example, let's say I use 7lbs of liquid extract and 1lb of cara pils, my estimated OG for 5 gallons will be:

OG = ( 35*7 + 20*1 ) / 5 = 53 (or 1.053).

As another example, if I want to target an OG of, say, 1.062 I could determine the needed amount of liquid extract:

62 = (35*x + 20*1) / 5, then x = 8.28 lbs of liquid extract.