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Blinded by Science: Calculate your IBU’s!

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September 11, 2015 by fhsteinbart


Typical IR spectrograph showing absorption peaks.

Typical IR spectrograph showing absorption peaks.

Just about everything home brewers need to do in regards to physio-chemical analysis can be done with simple instruments such as the thermometer and hydrometer.  But there are some numbers that can only be calculated using special instrumentalities like International Bittering Units.  Bitterness units as determined by the ASBC method of extraction using iso-octane followed by measurement of absorption of the extract at 275 nanometers (nm) supposedly expresses the bitter taste of beer regardless of whether fresh or stale hops were used.  This is done by using approximately 10 ml of degassed beer mixed with approximately 20 ml iso-octane, mixed thoroughly for 15 minutes.  The absorption of the iso-octane layer is then read by a spectrophotometer.  Bittering units are equal to 50 times the absorption of the iso-octane extracts which represents the isoalpha acids as found in hops.  The brewer than can state a number which gives the consumer some idea as to the balance of maltiness to hoppiness.  However, this is only part of the picture as we also have to consider the residual extract that the hop bitterness is counter posing.  In the end it’s all about the finish and resulting balance of that particular beer style.

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