Most people can tell you what ABV stands for when it comes to beer (alcohol by volume), but a little less known term is IBU’s.  International Bittering Units are used to describe how much bitter content is in a beer derived from hops in the brewing process.

Depending on where you look, IBU’s are either determined by how much isohumulone or isomerized alpha acid is in a beer (one part per million = one unit) or it is determined by an empirical formula [Wh × AA% × Uaa ⁄ ( Vw × 1.34 )].

In general if the the beer has a higher IBU, it will taste more bitter.  But this is not the rule.  We know that the bitter flavor is added to beer to help offset or complement the malty flavor of the beer.  Therefore those beer’s with a higher content of malts will also have a higher content of hops.  This then gives you a higher IBU for the beer but not more bitter flavor in the beer.

Here’s an example.  Guinness Stout has a high malt content and therefore starts out with about 50 IBU’s.  Most people would not say that Guinness is a really bitter beer.  On the other hand, take the same amount of IBU’s and put it in a beer with less malt, and you have an Indian Pale Ale (IPA) which is desired for it’s strong bitter flavor.

But in general you can say the more IBU’s a beer has, the more bitter a flavor it will have.  For those of you who are wondering, here is a general guide that I found on the web for how many IBU’s different styles of beer have.

A General IBU Guide:
Ales
Pale Ale / Amber Ale – 20-50 IBU
India Pale Ale – 40-60 IBU
ESB, aka Extra Special Bitters – 28-40 IBU
English Brown Ale – 20 IBU
Porter – 20-40 IBU
Irish Stout – 30-60 IBU
Barleywine – 50-100 IBU

Lagers
American Pale Lager – 10-15 IBU
Pilsner – 25-45 IBU
Bock – 20-30 IBU

--------------------