If you’ve enjoyed craft beer for a while you’ve probably seen the term IBU pop up on the side of a bottle, on the name of a beer, or in reviews on this blog. We’re going to take a look at what an IBU is, how it’s measured, and what it really means to you when enjoying a tasty barley beverage.
IBU stands for International Bittering Units and is the standard measurement of bitterness in a beer. The bitterness measured by IBUs is from the amount of hops added to the boil and how long you boil those hops. Hops excrete isohumulone oil, a compound known as an iso-alpha acid, which is responsible for the bitterness in beer. 1 IBU is roughly equal to 1 part-per-million of isohumulone oil.
The longer the boil the more isohumulone oil gets isomerized (changed from 1 arrangement of molecules to another arrangement of the same molecules) creating more bitterness. Most brewers boil beer for 60 minutes while some go for 90, or 120 minutes (hence the name of Dogfish Head’s 60 Minute IPA, 90 Minute IPA, and 120 Minute IPA). On the flip side of the increased bitterness longer boils equal less flavor and aroma you get out of that hop. This has resulted in breeding of specialized hops, some meant for bittering (Centennial, Galena, Nugget) with others for aroma or flavor (Cascade, Fuggle, or my favorites Galaxy, and Topaz). A few hop varieties work well for either bittering or flavor/aroma, most notably from this group for American beers are Citra hops.
Finding the IBUs of a Homebrew
Any homebrewers out there can calculate their IBUs using a few different formulas. Personally I use BeerSmith which does these calculations automatically so I’m not familiar with the formulas. Due to the complexity of these formulas I’m going to pass over covering them here. I suggest consulting your favorite homebrew book or checking out RoofTopBrew.net for the formulas and web-based calculators to figure out the IBUs for your recipe.
3 Things to Remember About IBUs
- Perception: We don’t perceive all IBUs equally. The maltier a beer is the less the IBUs matter. A malty 120 IBU Imperial IPA will not taste as bitter as a 50 IBU E.S.B. since the Imperial IPA pacts so much more malt. How can you know how malty a beer is? A good guess is to start with the ABV. The alcohol in beer comes from the yeast eating the sugar leached from the malt during mashing, so more alcohol = more malt. Your perception of bitterness will also change over time the more often you have bitter beers and the bitterer those beers are. They’ll make everything else seem less bitter by comparison.
- Perception Threshold: Most people cannot taste a difference over 120 IBUs. Some people will get more than that, some less, but no one will ever pick up on 500 IBUs vs. 1,000 IBUs. This is due to the number of receptors in our mouths and all of them getting occupied around the 110 IBU area. This doesn’t mean a beer can’t have more than 120 IBUs it just means you’re wasting hops, which are often the most expensive part of the beer.
- Other Sources of Bitterness: IBUs don’t account for all bitterness in a beer. Some types of malt, especially black malts, bring bitter flavors to a beer. However, most styles of beer don’t use enough of these malts/adjuncts to make a huge difference in flavor. Before the widespread use of hops brewers used various herbs and spices, known as gruit, to bitter their beer. A homebrewing colleague of mine is a fan of using rosemary to bitter his beers. Beyond different malts and spices there are a wide range of adjuncts that can add bitterness if used properly, and others if used improperly like when boiling the pith (that white stuff) of citrus fruits. No IBU formula takes any of these into account.
3 Beers to Demonstrate Different IBUs
Chimay Grande Réserve (Blue) – 30 IBUs – Barely bitter with just a hint under the malty sweetness.
Fuller’s E.S.B. – 35 IBUs – Medium bitterness for such a low-level of IBUs while toffee and caramel maltiness dominate the flavor. For only being 5 more IBUs than the Grande Réserve it is profoundly more bitter.
Stone Ruination IPA – 100+ IBUs – High end of medium bitterness that is far lower than what one would expect for “100+ IBUs.” More bitterness than Fuller’s E.S.B. but not much more and nowhere near 3 times more as the IBUs would imply.
4 thoughts on “Learning About Beer: IBU”
Nice post Tom, especially the comparison of beers with similar ibus yet different perceived bitterness. I wonder if you can suggest a barleywine or imperial stout that has comparable IBUs to ruination?
This post also got me thinking about some of the scientific aspects behind IBUs. If it leads to something worth a post I will let you know.
Look for anything American. Sierra Nevada Bigfoot and Stone Old Guardian both clock in around 95. Stone IRS is I think 90 or 95 as well.