The Skinny on Hops - Bitterness or Aroma?

Hops seem to be a big subject these days, and practically every ‘beer geek’ I come across wants to know “how many IBUs” (International Bittering Units) are in a given beer.  As mentioned in an earlier blog, IBUs are a direct measure of the amount of alpha acid from the hops (which is where the bitterness comes from) that are contained in a given beer, expressed as a ratio of mg of alpha acid per litre of beer.  A beer with 38 mg of alpha acid in a litre of the beer would then be said to have 38 IBUs.

While hop bitterness in beer is an important and necessary component of a beer’s flavor profile, hops also contribute aroma.  And since a major portion of flavor perception comes from one’s sense of smell, aroma is pretty damn important!  Paradoxically, the hop aroma profile of a beer has little to do with the level of IBUs – a beer with high bitterness can have little hop aroma, and vice versa.

This is because the bitterness compounds in hops (alpha acid) are fairly insoluble, and require long and vigorous boiling to become dissolved in the beer.  Unfortunately, the aromatic compounds, while readily soluble, are extremely volatile, and will “blow off” under the same conditions necessary to get the correct level of bitterness.  So if a brewer wants to add hop aroma to his beer, he must add hops at or near the end of the boil, after the boil, or in some cases, actually to the finished beer (dry hopping).  By adding hops while there is little or no boiling, the aromatic compounds can go into solution while the bittering compounds do not.

I raise these issues because some of the most pleasantly (and intensely) hoppy beers I have enjoyed over the last few years, have huge hop aromas but fairly low bitterness.  In my humble opinion, the lower bitterness adds significantly to the pleasant drinkability of the beer, and allows the focus to stay on the aromatic side of its flavor profile.  However, many consumers I talk to immediately correlate a highly hopped beer only with its IBUs, and are puzzled (and sometimes disappointed!) when they learn that the IBUs are lower than they would have assumed.  I can almost see them saying to themselves, “I thought I liked that beer, but it is not as hoppy as I thought.”  They completely miss the point that the “milder” beer may contain significantly more hops that the more bitter beer that they did not enjoy as much.

When a brewer formulates a beer, he tries to balance all of the flavor elements – malt, bitterness, aroma, yeast flavor – into a harmonious whole.  Choosing to make a highly hopped beer does not necessarily mean making an extremely bitter beer.  Trying to understand a beer’s hop character simply in terms of its level of IBUs is definitely missing the bigger picture of the complexity and harmony of its component parts.  A better understanding of the nuances a brewer can achieve with hops will certainly increase the pool of beer candidates for your home enjoyment.