Factors Affecting Hop Bitter Acid Isomerization Kinetics in a Model Wort Boiling System

摘要

Various factors were examined to determine their impact on the rate of isomerization of α-acids (humulones) to iso-α-acids (isohumulones) during kettle boiling. A model wort boiling system was used that employed multiple 12-mL stainless steel vessels to heat samples (α-acids in an aqueous, pH-buffered solution with other compounds included as specified) at 100℃ for 140 min. Concentrations of humulones and isohumulones were quantified at discrete time points using HPLC. Of the factors tested (glucose, maltose, calcium, and pH ranging from 4.8 to 6.0), none were shown to affect the rate of production of iso-α-acids. While pH had a marked effect on the concentrations of α-acids as measured, the differences may be attributed to solubility issues (since the solubility limit was approached and exceeded) that did not appear to affect the rate of iso-α-acid production.