CHANGES IN HOP α ACIDS CONCENTRATIONS ON HEATING IN AQUEOUS SOLUTIONS AND UNHOPPED WORTS

Abstract

α Acids were heated at various temperatures, pH values, and elapsed times in distilled water, in aqueous solutions of glucose, hydrolysed proteins, proteins, tannin and sodium carbonate, and in unhopped wort. Losses of α acids in aqueous solutions were low at neutrality, but below pH 5·8 they increased rapidly with side reactions becoming important. After the first 5 min. only relatively small further losses took place, especially in unhopped wort at elevated temperatures. In the first few minutes of heating, α acids disappear without concomitant formation of iso‐compounds. Later, iso‐compounds are formed in amounts substantially equivalent to the α acids which disappear. pH value is of more importance than presence of protein in governing the course of the reaction in wort. The unaccountable losses of α acids referred to in the literature take place within 5 min. of addition of α acids to unhopped wort. After the first few minutes of heating, losses of α acids follow the dynamics of a unimolecular reaction at pH values where side reactions are not important. 1964 The Institute of Brewing & Distilling