Subscribe to the OSS Weekly Newsletter!

Register for the OSS 25th Anniversary Event

How is IBU measured?

There are a number of qualities we look for when choosing a beer. IBU reports the bitterness, but where does this value come from?

I tried over 50 new beers in 2022. From Les Grands Bois here in Quebec all the way to Ucluelet Brewing across the country, my friends and I embarked on our own sort of brewery tour. The most memorable brews included Farmery’s Manitoba Maple Lager, Rebellion Brewing’s Lentil Beer, and Tofino Brewing’s Kelp Stout. As these names suggest, we selected our flights based off of funky ingredients and good advertising. But along the way, we learnt to read past the names and inspected the vital stats reported for each drink, including ABV, SRM, and IBU.

IBU or “International Bitterness Units” is a scale from 0 – 120+ that gauges a beer’s bitterness level. As a new beer drinker, I found that I tended to lower IBU beverages like light lagers or blonde ales. But every now and then I’d pick (and enjoy) an IPA, which ranges on the higher end of reported IBU levels. Why was it that sometimes I’d agree with the reported bitterness and sometimes be surprised?

IBU is a chemical measurement of bittering compounds called iso-alpha-acids. It’s common that other ingredients in the beers will mask or alter the flavour profile, especially if you’re one to grab a can with something like kelp on the label. However, the measurement of IBU is very scientific and reliable!

In the most basic terms, beer is made of water, malt, and hops. The latter ingredient is the star of the show, providing flavour, aroma, and typical bitterness. When beer is brewed, alpha acids present in hops will isomerize (take new shapes), forming different iso-alpha acids. Imagine the marshmallows in a bowl of Lucky Charms cereal — slightly different shapes but all strikingly sweet. In order to measure IBU, a sample of beer is combined with an acid and a solvent. The acid will draw out the iso-alpha acids and allow them to be captured by the solvent. A sample of this solvent is then analyzed using spectrophotometry, where a beam of light passes through the liquid, identifying compounds with a target light absorbance of 275 nm. The spectrophotometer gives an absorbance reading, which is multiplied by 50 to give IBU!

Just like how a marshmallow per cereal reading would tell us how sweet our breakfast will be, the iso-alpha-acid concentration in a beer will tell us how bitter it should taste. And that’s IBU. Many flights and a bit of science later, I know how to choose the best beer to ring in the new year!


Back to top