Lesson 9 - Brewing with Hops SAQ
This lesson allows you to test yourself on the material covered in the previous lesson, Brewing with Hops, and determine the level to which you have attained the outcomes.
Suggested Response - Q1
*Define what an IBU is and provide an overview of how it is measured.
Response:
Spectrophotometry is used to measure the bitterness level in the wort or beer. Results are reported in bitterness units (BU) or international bitterness units (IBU).
In this method 10 mL of degassed, acidified beer is extracted with 20 mL of iso-octane. After centrifugation, the absorbance of the iso-octane containing the extracted iso-α-acids is measured in a spectrophotometer against a blank of pure iso-octane, at a wavelength of 275 nm. The measured absorbance is then entered into the following equation:
International Bitterness Units (IBU) or Bitterness Units (BU) = Factor x Absorbance
It is usually assumed to be around 1 mg of iso-α-acids in 1 L of beer but IBU is not the same as mg/L iso-α-acids as measured by HPLC.