I asked the boys this and here is what they said: "Kraven, beer is typically measured for bitterness in International Bittering Units (IBU). This number can be theoretically calculated in the brewery but is only truly accurate via laboratory analysis. Technically 1 IBU is 1 milligram of isomerized alpha acid per liter of liquid. The higher the IBU number, the more potential bitterness. As usual in brewing though, it depends. The stronger (higher gravity) the beer, the less perceived bitterness. For example, 60 IBU in a 5% ABV pale ale would be perceived much more bitter than 60 IBU in a 10% ABV pale barleywine. Beer drinkers should keep in mind, numbers don't really drink well so don't get too hung up on them".