Hello, Congregants. Welcome to the Pastoral Counseling feature of Ale Evangelism. In this feature, we will attempt to answer the questions asked by friends and readers to bring us all to a better understanding of beer appreciation.
Today’s question is one that I usually don’t get asked until after more in-depth craft beer discussions with friends and family. Craft brewers are blessedly starting to put more information about their beers onto their labels these days, which helps those of us attempting to copy their great successes in our own homebrewing attempts. The IBU (International Bitterness Unit) rating of a beer describes (sort of) how bitter a beer is. It is derived from a formula which objectively attempts to describe how bitter a beer is by taking into account the alpha acids present in the hops used, which is further modified by when said hops were added to the boil. The scale goes from about 5 or so IBU’s to 100 IBU’s. Light lagers will generally be in the neighborhood of 5 IBU’s, while India Pale Ales can be upwards of 100 or more IBU’s. The question, however, is this: Why don’t high-IBU beers always taste super bitter? Read more to find the answer…
The short answer is that the IBU rating of a beer does not necessarily measure how bitter a beer is. I realize this is sort of counter-intuitive considering the name, but them’s the facts, congregants. IBU’s, as I said above, actually measure the precise amount of alpha acids contained in a sample of beer. Alpha acids are one of two acid compounds that hops impart to a beer, the other being beta acids. Alpha acids impart both bitterness and a protection to the beer into which they are dissolved. Alpha acids protect beer from bacteria, thereby acting as a preservative. Beta acids are less relevant to this article, but they impart their aromas to the beer. Beta acids are broken down during the boil, while alpha acids persevere, so your bittering hops are added to the boil early on, while your aromatic hops are added toward the end of the boil.
How this relates to IBU’s are fairly simple to explain. Humans perceive alpha acids as bitterness. However, that perception is modified by the amount of sweet malt used in the recipe. A high-malt, high-gravity beer with an IBU rating of 60 might actually taste less bitter than a low malt pale ale with an IBU rating of only 35. The greater amounts of malt in an imperial stout will often offset the amount of bitterness perceived. So when you read the IBU rating, you will want to take the style into consideration. If it’s a very malty style like a Scotch Ale, a sweet, Scottish Stout, or even something BIG like a Russian Imperial Stout, the result will be less perceived bitterness. In the case of the latter, the bitterness will simply be incorporated into your perception of the roasted flavors from the roasted barley used in the recipe.
For this reason, IBU’s aren’t always a useful rating except when comparing like to like when it comes to beer styles. An IPA with a rating of 100 WILL taste more bitter than an IPA with a rating of 90, assuming their malt levels (measured in Original Gravity; a topic for another day) are roughly equal. However, when comparing styles with vastly differing levels of malt, the IBU rating is a less precise way to estimate the perceived bitterness of a beer.