Hop bitterness

This is a follow on article from the recent All about hops article.

So back to hops…

The bitterness from hops is created from chemicals referred to as alpha acids (humulone, cohumulone and adhumulone if you must know). These reside in the soft resin part of the hop flower. Try rubbing some hops in your hands and you will soon learn about their resinous nature. Alpha acids are not naturally bitter to taste, but boiling isomerises these chemicals to produce the bitter tasting compounds found in beer.

Each hop variety has a different proportion of alpha acids, which means some varieties will make beer a lot more bitter than others. The German Saaz variety has very low alpha acids (~3%, used for flavouring German lagers); the classic English Fuggle is middling (~5%, used for bitterness and flavour in English ales), and some new world hops (such as Chinook) are just stupid (up to 14%, used by American hop-heads).

The bitterness in beer is measured using the aptly named International Bitterness Unit (IBU). The bigger the number, the more bitter the beer. Beers tend to start at maybe 20 IBU (very low bitterness) and can go up to 80-100 IBU (turns your face inside out).

Here are some example IBUs of commercial beers (these may not be totally accurate, but are given just for interest):

• Banks Mild  25 IBU
• Theakston’s Old Peculier  29 IBU
• Marston’s Pedigree 35 IBU
• Black Sheep Riggwelter  39 IBU
• American IPA  ~ 60-70 IBU
• Imperial (or Double) IPA  ~100+ IBU