At ComposeMD, we do not brew beer. We do, however, have some experience in its consumption. There was a time when the decision boiled down to Natural Light or Milwaukee’s Best. But since those days, the choices have multiplied exponentially. Over the years, we’ve also noted the increased prominence of certain abbreviations. We got the ABV one down. That’s alcohol by volume, expressed as a percentage, with the higher values indicating a much higher need for a designated driver. And we sort of have a sense of this IBU thing, with the higher values more likely to make us reach for the french fries, not that it takes much for that to occur. But what does IBU stand for? And what exactly does it mean?
Definition
IBU stands for International Bitterness (or Bittering) Unit. It is a standardized measure that quantifies the concentration of bittering compounds that are in a beer. Such compounds originate from the hops used in the brewing process. (Hops, which are the flowers of the Humulus lupulus plant, are used both for the purposes of flavor/aroma and preservation.) The major substances of interest are called alpha acids. When heated during the boiling process, they undergo a chemical transformation called isomerization to form iso-alpha acids. A common alpha acid is humulone, and isohumulone is therefore often mentioned as a key contributor to IBUs. Certain hop varieties have more alpha acids than others, thus resulting in more IBUs. A technique called dry-hopping refers to adding hops after the boiling process, contributing to flavor/aroma but not to the generation of iso-alpha acids (or IBUs).
The measurement
Laboratory methods such as spectrophotometry and high-performance liquid chromatography (HPLC) can be used to formally measure the concentration of iso-alpha acids as well as other auxiliary bittering compounds. The results are reported in parts per million and converted to the more relatable IBU scale.
The IBU scale can measure from 0 up to very large numbers. The aforementioned Natural Light finds itself at 5 IBUs, while many beers land in the 20-45 range. With the proliferation of India Pale Ales (IPAs), it is not uncommon to find offerings in the 70s and 80s. Apparently, certain beers have found themselves in the thousands.
Given the relative precision of this measurement, IBUs can actually be an important quality control metric, especially for larger brewers who are heavily reliant on consistency.
Translation into Real Life
All that chemistry is fine and all, but how does it translate to the consumer side? There seems to be a consensus among those in the brewing world that the measure of IBUs may be overhyped and misunderstood. Yes, some correlation exists between IBUs and the human perception of bitterness. However, the correlation can break down based on other factors in the brewing process, such as how much malt is used. (Malt adds sweetness that can balance the bitterness.) The end result is that certain high-IBU beers can come off as not particularly bitter, and certain low-IBU beers can be more bitter than advertised.
In the end analysis, to truly gauge the bitterness of a beer, you will simply have to try it. Our guess is that this recommendation will not be a major problem. Just don’t forget the french fries.
2 Responses
ha.ha. I can make it conversation starter with my beer drinking friends.
IPAs have got anything to do with India? Indian indians have this funny theory that anything bitter is good for diabetes. neem, karela etc.
Oh,my, they might start drinking more bitter beer.
finally, human is better than machine for taste index,[TIU]
Yes, even in the era of big data, humans are still key (for now…haha). By the way, there is definitely mention of the health benefits of certain compounds in hops, including isohumulone, for things like glucose tolerance. That said, given all the other stuff in beer, touting beer as good for diabetes is definitely wishful thinking. Finally, in terms of the term India Pale Ale, there seem to be several different explanations. Here’s one taken from bon appetit.
“The IPA was invented in Britain. Here’s the abridged version: British sailors, while sailing to India, loaded up barrels of beer with hops, because hops were a preservative. The hops hung around in the beer for so long that they lost their fruity flavor and left a bitter tasting beer.