The most important bitter substances in wort and beer are the iso-α-acids. In addition, β-acids and δ-acids can be identified as well, primarily in the wort. Furthermore, wort and beer contain other derivatives from the acids of the bitter substances found in hops, particularly products of oxidation, which can also contribute to the bitterness in beer.
Simultaneous determination of iso-a-acids and reduced iso-a-acids (rho, tetra, hexa) in beer and beer-based beverages using HPLC
This method is not suitable for beer and beer-based beverages containing a mix of hexa- and iso-products (co-elution).
This method separates iso-α-acids and reduced iso-α-acids (rho, tetra, hexa) chromatographically [2].
The separated compounds are detected spectrophotometrically at 270 nm. Quantification is performed using International Calibration Standards (ICS).
These standards do not contain all of the isomers of a certain type of iso-α-acids. Currently, ICS-I (DCHA-Iso) contains only the trans-isomeric complexes with dicyclohexylamine (DCHA). ICS-R (DCHA-rho) only has the cis-isomers in a complex with DCHA. ICS-T (tetra) comprises both cis- and trans-isomer complexes with DCHA, and ICS-H (DCHA-hexa) includes only cis-isomers with DCHA.
Commercially available hop products contain a greater number of isomers than the standards.
Thus, there are more peaks in the chromatogram than in the corresponding international calibration standards, in particular, with the cis-iso-cohumulone as well as the cis-iso-n-humulone and cis-iso-ad-humulone. The application of this method to these kinds of beers should be conducted with this in mind, since it is not entirely known whether these additional peaks are actually isomers of iso-α-acids.