I Tried It: Calculating My Malt Bill By Hand

Determining to which generation I belong seems to be a nebulous exercise because, being born in 1980 (for those of you actively trying to calculate my age now, I'll save you the time and tell you I'm 37) makes me a Gen X-er, a Gen Y-er, a millennial, or the amalgamated Xennial. 

Which is all to say that I didn't have to wear a bike helmet as a kid (because head injuries from bikes weren't invented yet?), I didn't own CDs until late high school, and I had to take a test on sending "electronic mail" in my freshmen year of college. A TI-86 was a fascinating piece of technology and I know how to properly write a check. 

However, like most people, I rarely rely on my own knowledge to recall anything and I almost exclusively rely on various software, apps, and algorithms to determine how I move through my daily life. 

This reliance naturally extends to my homebrewing. I use BeerSmith and Bru'n Water software to develop my homebrew recipes and serve as a check on brew days to make sure something hasn't gone awry in my process. For those of you unfamiliar with BeerSmith, it's homebrewing software that allows you, among other things, to accurately design homebrew recipes consistently without having to calculate all the variables that go into a homebrew recipe, like hop additions, yeast pitching rates, malt bills, and conversions. (SN: There are other homebrewing software programs out there, but I started homebrewing using BeerSmith and haven't felt the need to try other programs.)

I recently began reading Designing Great Beers by Ray Daniels, which was originally published in 1996 and updated in 2000. It predates homebrewing software and beer recipe websites. Because there exists a plethora of information on homebrewing online now, this book is a fantastic exercise in learning the why behind the how of many aspects of homebrewing.

I'm probably not going to use dilution to determine beer color anytime soon beyond possibly as an academic exercise, but having learned my hobby solely by doing data entry into a software program has left somewhat of a hole in my brewing knowledge, namely when it comes to how to determine what proportions of what kinds of malt to include in a recipe. It is not difficult to read books or other sources of information on what malts to include in classic beer styles, but determining what amounts are a different story.

Thus, one day when I was feeling particularly inspired to write out some equations by hand on a piece of paper, I decided to eschew technology in favor of calculating the malt bill by hand for a double IPA I had been thinking about brewing.

The result: it's actually pretty easy and fun to do.

To calculate your malt bill by hand, you need four pieces of information:

1. Target gravity of the style or beer

2. Finished volume of batch

3. Fermentable ingredients & approximate proportions

4. Extract efficiency

In my instance, the target gravity for a double IPA is 1.065-1.085, which I got from the BJCP Guidelines (I decided on using 1.075 as my target gravity); my batch size was 5 gallons; my extract efficiency is approximately 71%; and my fermentables and proportions were as follows:

• 2 row = 86%

• Crystal 40 = 4%

• CaraPils = 4%

• Dextrose = 6%

The next step is determining the total number of extract needed, which is the final volume of beer multiplied by the gravity, expressed in gravity units:

5 gallons x 75 GU = 375 GU of total gravity

Now that I knew the total gravity I needed to get from all the fermentables, my next step was figuring out the proportion of total gravity I needed to get from each of my fermentables, which I calculated by multiplying each ingredient's percentage of the total grist by the total gravity:

• 2 row = .86 x 375 = 322.5 GU

• Crystal 40 = .04 x 375 = 15 GU

• CaraPils = .04 x 375 = 15 GU

• Dextrose = .06 x 375 = 22.5 GU

Once I had the ingredient gravity, I could calculate the amount in pounds of each one of my fermentables. To do that, I divided the ingredient gravity by the amount of extract possible from each pound of malt, where gravity per pound of malt is equal to mash efficiency multiplied by maximum extract:

Ingredient gravity/(mash efficiency x maximum extract)

There are several places where you can find a table of typical malt yields, including in Designing Great Beers and the online version of How to Brew by John Palmer, so you can check those to see where I got the below extract potentials of each fermentable:

• 2 row = 38

• Crystal 40 = 34

• CaraPils = 32

• Dextrose = 37

Thus, I calculated the pounds needed of each ingredient:

• 2 row = 322.5/(.71 x 38) = 11.95 lbs

• Crystal 40 = 15/(.71 x 34) = .62 lbs

• CaraPils = 15/(.71 x 32) = .66 lbs

• Dextrose = 22.5/(.71 x 37) = .86 lbs

And voila! I knew how much of each fermentable I needed for the malt bill of my double IPA. After I calculated everything, I plugged my grain amounts into BeerSmith to double check my math and ended up with a target gravity of 1.075. 

Knowing how to calculate the grain bill also came in handy when I was weighing out my malts at the homebrew store because I had originally started with a target gravity of 1.069 and then decided to increase the gravity after I had written my shopping list. Armed with my formulas, I quickly calculated the additional amounts I needed for the increased gravity. 

Quick calculations at the homebrew store

Going forward, I anticipate that I'll calculate the malt bill by hand more often, but probably not all the time. However, it was incredibly educational and much less intimidating than I thought, so I highly recommend that homebrewers try it at least once.