Interaction of proteins and amino acids with iso-α-acids during wort preparation in the brewhouse

This paper investigates the binding behavior of iso-alpha-acids from hops on free wort amino acids and proteins concerning the wort production process in breweries. The studies were carried out with different amino acids, bovine serum albumin and wort. To identify the nature of reaction between iso-alpha-acids and these substances, analyses of free amino nitrogen, HPLC and isothermal titration calorimetry were performed. According to the results, the iso-alpha-acids do not form covalent bonds with free amino acids of wort. However, iso-alpha-acids, especially isohumulone and isoadhumulone, form ionic bonds with wort proteins. A distinction must be made between proteins that are present in the hot trub, and those that are still dissolved in the hot wort. Proteins that are already coagulated and precipitated no longer react with iso-alpha-acids. Future experiments will investigate whether the established ionic bonds between iso-alpha-acids and proteins from the wort preparation process are maintained during fermentation until the finished beer or beer foam. If this is the case, which is induced by the experiments, there is a measurable loss of iso-alpha-acids in the hot wort, but at the same time, a gain for the later beer foam retention, as the iso-alpha-acids will stabilize it.

Automated summary

The study shows that iso-alpha-acids in hops form ionic bonds with wort proteins, but do not covalently bind to free amino acids in wort. Coagulated and precipitated proteins no longer interact with iso-alpha-acids.