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I'm confused by the whole idea of IBUs. I see a lot of IPAs that are rated in the 40s or 50s for IBU, but in practice they are much more bitter than stouts in the 80+ range. Shouldn't the IPAs have a higher bitterness rating? What's the point of the rating?

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IBU is a measurement of the chemical concentration of iso-alpha acids, not the perceived bitterness. Malty tastes do suppres the perception of hop bitterness. See wikipedia on beer bitterness 1 and its literature list.

A heavily malty beer, which a stout is, requires way more chemical hop bitternes to achieve the same perceived bitterness as a light pilsner.

Excuse me going anecdotal, but at one time, friends and me brewed an ale with an unholy amount of hops (150g @ 11% for 22l). When it came to hop additions, we decided to just dump in all the hop bags from the freezer. This ended up to be around 100 IBU after correction for ageing.

Now, quite clearly, the resulting light ale was on the very edge of being consumable, but with some aging and getting used to it, it became a very very good ale, which all the hoppy people loved.

The same amount of hops in an irish stout would probably be "meh".

  • What's the point of the IBU metric, then? – SPavel May 18 '16 at 19:09
  • Not much. It can be useful to compare the perceived bitterness of similar beers. Say, lets have a look of continental europilsners. They are mostly not malty, and a brand like Jever stands out with its ~30 IBU. On the other hand, an ale I brewed with around 100 IBUs is on the verge, but not too bitter. – Posipiet May 18 '16 at 19:22
  • Stouts get some of their bitterness from the roasted barley: Think of black coffee, which is bitter. Perhaps you are thinking of an imperial stout where a very high gravity from malt must be balanced by a high hop IBU. An Irish Dry stout is a low gravity beer that may be as low as 35-40 IBUs. – jalynn2 May 20 '16 at 20:44
  • Was your 100 IBU measured? If not, do commonly used formulas for IBUs hold for such high values? I'd expect they break down at some point (I'm not suggesting your brew was not really 100 IBU, I'm genuinely curious!) – fqq Jun 6 '16 at 9:48

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