When is an IBU not an IBU

It's the bitterest beer in the world!

It seems that every week we hear breathless reports about the newest biggest beer of 100+ IBUs (International Bittering Units) — a beer purported to contain in excess of 100 milligrams of isomerized alpha acids per liter of beer.

(To put this in perspective, most mainstream industrial lagers contain less than 20 IBUs, and more often in the single digits.)

These claims are usually based upon simple arithmetic calculations, not on more expensive —and precise— spectrophotometric analyses. And then, you'll hear: "It was such a balanced beer for such a high bitterness."

To borrow from Jon Binkley, as quoted by Lew Bryson at his blog Seen Through a Glass:

Specific Gravity only captures one narrow aspect of "MALTY," just as IBUs only capture one narrow aspect of "HOPPY." Neither addresses FLAVOR.

Listen to this Basic Brewing podcast interview of John Palmer of Brew Your Own Magazine by host John Spencer.

Palmer reports on the International Brewers' Symposium on Hop Flavor and Chemistry, held at the University of Oregon in August 2007.

Research by Val Peacock of Anheuser-Busch, among others, debunks some long-held memes of craft-and-home-brewing.

For example, an IBU is not necessarily one part per million of isohumulone. It is in fact more inclusive and more externally-affected than that.

Wort gravity does not in and of itself reduce isomerization kinetics, that is reduce the efficiency of hop bitterness extraction. (It's the increased hot-break matter onto which more of the iso-alpha acids adhere.)

And one that fascinated me: a 20 IBU beer brewed with hops prevalent in 1968 —the year when many of the current standards were adopted by the American Society of Brewing Chemists (ASBC)— will be perceived to be different, bitter-wise, than a 20 IBU beer brewed from newer hop varietals of today.

The site is Basic Brewing, essentially a podcast and video blog for homebrewers. But this hop report is, at least, a cursory good listen for many craft brewers.