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Science Friday: IBUs

Nov 22, 2013 Comments (0)  | Tags: Beer Geekery Science Friday: IBUs

Here at Ninkasi we take our hops seriously. The names of some of our hoppiest brews often reflect this dedication: Critical Hit, Tricerahops and, of course, Total Domination! If you’ve tasted each of these hoppy beers, you probably can tell us one thing that they all have in common: a delicious, bitterness! Do you know what causes the delicious bitterness that we love in all of these beers? Well, since we’ve been talking about it all paragraph, you probably can—it’s the HOPS!

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Hops are little cones of bittery goodness which brewers have been using for hundreds of years to help with aroma, flavor, stability and preservation. Different acids in the hops help add different elements to the beer: alpha acids in the hops add flavor, while beta acids supply the beer with a strong fruity and/or earthy aroma. Alpha acids are also primarily why hops were used in the early brewing days – to provide a mild antibiotic property against beer spoiling microbes. There’s a lot to love about hops! Did you know that each and every time you order a beer, there is a measurement to help you determine just how bitter and hoppy a beer is going to be? Developed in the 1950’s, brewers and chemists have been using International Bitterness Units (IBUs) as a method of differentiating low bitterness from high bitterness. If a beer’s IBU is really low (like our Quantum Pale Ale at 35 IBUs) it means that there is lower concentration of bittering flavor. But if it’s higher (like our Tricerahops Double IPA at 100 IBUs) it means that there is a higher concentration of bittering flavor.

Here’s a little background on how we get to these numbers:

When testing for IBUs the molecule that is responsible for the bittering flavor is Isohumulone (or as no one calls it):

3,4-Dihydroxy-5-(3-methylbut- 2-enyl)-2-(3-methyl-1-oxobutyl)-4-(4- methyl-1-oxopent-3-enyl)-1- cyclopent-2-enone


To determine IBUs a cold sample of beer is acidified and degassed. The acidification helps to dissolve the isohumulone and pull it out of the beer. Then a non-polar solvent is added to extract out the isohumulone from the beer. Here at Ninkasi, we use iso-octane for extraction (or):



Using a centrifuge, the beer is separated, like oil and water, from its bitterness molecules which are now floating in the iso-octane layer. A spectrophotometer is then required for measuring the iso-octane layer at a wavelength of 275 nanometers. One IBU is equivalent to one part per million (ppm) of isohumulone. The higher the concentration of alpha acids, the higher the IBUs.

When a beer contains 100 IBUs, scientifically speaking, it has 100 milligrams of isohumulone per 1 liter of beer. That’s a lot of hops.


Now, off to drink a Tricerahops (100 IBU). Cheers!

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