Ask Mr. Wizard

Developing a Brewing Calculator


Gary Fisk — Americus, Georgia asks,

An important part of my homebrewing hobby is the development of web-based brewing calculators. The biggest challenge is finding good technical information. Web searches often yield vague results, formulas with errors, or formulas based on non-metric units. Where do professional brewers find high-quality technical information? Which books would you recommend for technical reference purposes?


I also consider developing my own calculation tools a key part of my hobby and, previously, part of my job as a commercial brewer. I have a pretty handy collection of calculations and will touch on what has been valuable to me along my tool-making journey, starting with your question about sources used by professional brewers. The short answer is brewing school. Whether brewers take brewing classes in universities like Weihenstephan, UC-Davis, KU Leuven, Oregon State, Heriot-Watt, Auburn, and Virginia Tech, or through private brewing schools like Siebel and the American Brewers Guild, the same basic beer math is taught. And these days, it’s all taught using the metric system.

Perhaps the most fundamental group of brewing calculations are those related to wort and brewhouse yield. All schools teach students that kg extract is equal to liters of wort multiplied by the product of wort specific gravity (kg per liter) and wort Plato (kg of extract per kg of wort). This basic relationship opens up a whole set of calculations related to mash calculations and efficiency. Textbooks like Kunze’s Technology Brewing and Malting and The Comprehensive Guide to Brewing (Gabriela Basarová, Jan Savel, Petr Basar, Pavlína Basarová, Tomás Lejsek) include examples of these equations and how they are used. Another really helpful book is Steve Holle’s A Handbook of Basic Brewing Calculations published by the MBAA (Master Brewers Association of the Americas) in 2003.

When it comes to hop math, there is really only one equation universally used and that is how to calculate hop charges based on some level of bitterness in terms of international bitterness units (IBUs). Unfortunately, the golden key that makes hop calculations tick is the elusive utilization term; most brewers refer to tables relating utilization to boil time, wort gravity, and hop preparation type. Some brewers calculate oil contribution based on hop analytics, but this is not commonly used.

There are also a range of brewing calculations related to mashing-in, mash heating and boiling, wort heating, boiling and cooling, and beer blending and dilution. These calculations are all based on fundamental math used in food engineering/processing. Much of this is left out of brewing texts and is the sort of topic often left to classroom lectures. The good news is that Q = MCp∆t is the key to all of the heating and cooling equations (Q is heat energy, M is mass, Cp is specific heat, and ∆t is temperature change). The only obscure constant that can be hard to find is the specific heat of malt. The specific heat of malt and other brewing grains is about 1.8 kJ/kg*Kelvin (0.43 BTU/lb.*F).

Another great source of information about brewing calculations is found on brewing ingredient and process aid specification sheets. My brewing calculation workbook includes separate tabs for usage rates of beer finings, enzymes, and nutrients. These are the sorts of tidbits of information that can easily be added to your library of nuggets as you try new things.

And finally, there is water. I am a picky user of tools and really don’t like any water calculator that I have trialed and wrote my own water tool based on the water basics first laid out by Paul Kolbach in the early 1950s. 

Response by Ashton Lewis.