What is an HBU?
HBU stands for Home Bittering Unit and is also known as an Alpha Acid Unit. HBU’s were developed as a method of standardizing the total bittering potential of hops in order to mitigate the variation in Alpha Acids (AA%) from season to season and hop to hop so that the bitterness of beer recipes will be 100% consistent from brew to brew. One of the first questions someone asks about using HBU units is why do I need to use HBU if I’m using the same hop I did for my last brew? Even though it may be the same hop, hop plants grow in AA% from year to year until the plant is split and AA% returns to desired levels, only to repeat the cycle. Identifying the bittering level that is desired and calculating a specific HBU to bitter the recipe in a standardized manner guarantees consistency in bittering from brew to brew without affecting any other aspect of the recipe.
How is HBU Calculated?
The second most common question after convincing a guest about the benefits of consistency in brewing is: How do I calculate HBU? An HBU value is calculated by multiplying the amount of hops (oz) by the Alpha Acids.
OZ * AA% = HBU
Example: 1 oz of Northern Northern brewer at 9.6% Alpha acids is 9.6HBU’s.
1 oz * 9.6 AA% = 9.6 HBU
When the AA% changes between batches of hops and the next batch AA% has suddenly risen from 9.6% AA to 19.2% AA, but the original 9.6 HBU’s are what’s needed to reproduce last year’s recipe, just use algebra.
Xoz * 19.2 AA% = 9.6 HBU // Divide (9.6/19.2) to solve for X, X = ½ oz
½ oz is how much would be needed at the new AA% to reproduce the same bitterness as the last brew that had 9.6HBU.
What Hops Can be used for HBU?
A common third question we get about home bittering units is: Can I use any hop I want to get the correct bittering levels? The answer to this is not as simple as the first two. Mathematically speaking one can calculate HBU bittering using any hop their heart desires. However, in reality one would want to use a neutral hop like Northern Brewer, Magnum, Cluster or Challenger that will not impart any flavor profile into the beer. Examples of hops to avoid when calculating bittering units are Chinook, Citra, Centennial, Polaris, etc. These hops are known for their potent citrus and/or piney profiles. And while they can be adjusted mathematically to deliver the correct bitterness, their strong flavor profiles could potentially carry into your brew, even though their flavor oils should have been driven off by the boil.