Sensory and Analytical Characterisation of Reduced, Isomerised Hop Extracts and Their Influence and Use in Beer

Abstract

The use of reduced, isomerised hop extracts became very popular during the last decade in terms of achieving both better foam and light stability. Today the most common products are those with tetra-hydro-iso-α-acids (THIA) or rho-iso-α-acids (RHIA). There is still not clarity concerning the taste properties of these products in comparison with iso-α-acid Bitter Units (BU). The experiments conducted showed that the bitter conversion factors determined in previous work (1.6 for THIA and 0.7 for RHIA) represented only perceived bitterness when presented in tap water. In the test beers a bitter conversion factor of 1.0–1.1 for THIA was determined and the factor of 0.7 for RHIA in beer was confirmed. Photometric methods led to considerable deviations when used for the determination of THIA and RHIA, whereas the HPLC method, in combination with either Solid Phase Extraction (SPE) or Liquid Liquid Extraction (LLE), led to very good results. RHIA was found to have a foam stabilising effect and it was also shown that the foam stabilising effect of THIA in unhopped beer was higher than in hopped beer. The quality of bitterness decreased with an increase of THIA and RHIA. A dependency on the alcohol content in regard to the bitter intensity was ascertained.