This is not really something you need to know (unless you’re a beer nerd), but I wanted to clarify and expand my initial definition. A beer’s IBU is measured by the amount of hops used and their acid content. So yes, the higher the IBU, the more bitter the beer. This can be misleading, though and I’ll give you an example. If you look through the tasting notes on my previous posting, you’ll notice that the Cherry Imperial Stout has the highest IBU number and I didn’t mention anything about it being bitter. The malt sweetness in this beer is playing against the bitter hops.
Also, hops aren’t the only culprit – roasted malts (think espresso), lower serving temperature, higher carbonation and a low residual sugar content can all make a beer seem more bitter. Bitterness makes a beer refreshing and is necessary to balance out the sweetness of the malt. It is also the backbone of the beer’s structure – think tannin or acidity in wine. So, please don’t think of bitter as a dirty word.