To change a chemical compound into an isomer of the same compound. An isomer has the same chemical formula, but the atoms are arranged in a slightly different fashion. Hops must be boiled for extended periods because alpha acids are not soluable in wort, only iso-alpha acids are. Boiling isomerizes the alpha acids.

To alter the arrangement - but not the kind or number - of atoms in a compound by heating or other means. During boiling, alpha acids are isomerized and these isomers (iso-alpha acids) bitter the finished beer.

cause to change into an isomer