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Understanding Bitterness

Brewers at The Boston Beer Company ran trials to determine how common spices changed perceived bitterness in various beers. They found that there’s more to bitterness than isomerized alpha acids and more to measuring IBU than those isomerized compounds.

Stan Hieronymus Nov 29, 2017 - 9 min read

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Frustrating as brewers find it, any effort to measure bitterness analytically complicates it. Perceived bitterness? Quality of bitterness? These are the domain of sensory panels. With the current technology, says hops scientist Val Peacock, machines are not ready to replace tasting panels. “I hope to be proven wrong in the next ten years,” he says. “My goal in life is to prove myself wrong.”

Brewers who are adding increasingly large quantities of hops late in the brewing process, particularly post boil, have made the math more complicated. Intent on maximizing the impact of aroma, they are changing the matrix of bittering compounds in ways scientists had little reason to investigate until now.

IBU, Hops, and Bitterness Aren’t Synonyms

The elephant in the bitterness room is the IBU, originally an acronym for international bitterness unit, but now often a synonym for “brewer used a lot of hops.” It is determined by acidifying and extracting a sample of beer, then taking an absorbance reading at a specific wavelength with ultraviolet light. The procedure must be performed in a lab, and the result is an absolute, a single number that is generally misunderstood. To estimate IBUs, a formula emerged more than fifty years ago as a compromise among brewing scientists on both sides of the Atlantic. (Many small breweries, as well as homebrewers, use formulae or software to calculate IBUs. The greatest weakness of such tools is that utilization is a key component, is often brewing-system specific, and is seldom well calibrated.)

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