Alpha acids (α-acids) are the main compounds responsible for bitterness in hops.

• Conversion into iso-alpha-acids: during the boil, the α-acids are isomerized into iso-alpha-acids, which are soluble and bitter.

• IBU (International Bitterness Unit): the amount of iso-alpha-acids dissolved in the beer determines the IBU.

• Factors influencing bitterness:

  • Boil duration (longer → more bitterness)

  • Original gravity of the wort (sweeter → lower perception of bitterness)

  • Amount and % of alpha acids in the hops

Alpha acids are therefore the chemical heart of bitterness, and their dosage and timing determine the final profile of the beer.