[Evaluation of the quality and application in the brewing process of advanced hop products based on bitter acids and aromas]

Hops (Humulus lupuliis L.) are essential for the production of beer. All brewers use hops in their brewing process because hops have a unique effect on the flavour and physical appearance of the final product. The most important hop fractions are the unique hop acids and the hop oil, which are both found in the lupulin glands of the female hop cones. The hop acids consist of the alpha and the beta-acids. Among the hop acids, only the alpha-acids or humulones have an essential brewing value. During wort boiling, the alpha-acids are converted to the iso-alpha-acids, which are largely responsible for the fine bitterness of beer, but equally important for a good foam stability. On the other hand. it is generally accepted that the hop essential oil contributes to the hoppy aroma and flavour of beer, through an array of sensory impressions. The traditional use of unprocessed raw hops has several major disadvantages, such as the low bulk density of the hop cones, the stickiness of the lupulin glands, the heterogeneity with regard to the alpha-acid and hop oil content, the extreme sensitivity of these important brewing constituents to oxidation, and, in particular, the poor efficiency in terms of utilisation of both the alpha-acids and the essential oil. As a consequence, a wide range of hop products are available today for the production of consistent high-quality beers. Hop products are classified in two groups, known as conventional hop products (i.e. various forms of hop pellets and kettle hop extracts to replace whole hops in the kettle), and advanced hop products with specific formulations (f. i. isomerised hop extracts, reduced isomerised hop extracts, and various advanced hop oil preparations). In particular the advanced hop products are used increasingly, especially by large breweries, to attain improved flavour consistency of existing brands and to develop new beers with specific organoleptic properties. In contrast, small and medium-sized breweries remain largely deprived of this new hop technology, nowadays also called "High Tech Hopping". In this study which was carried out in the context of the HOBU-Project 970117, the application of various advanced hop products was evaluated in comparison with hop pellets Type 90 as reference material. The emphasis was put on the use of isomerised hop extracts, reduced isomerised hop extracts and pure hop oils. The advanced hop preparations were added at different stages in the brewing process of both lager and top-fermented beers. The experimental brews with the hop products and the corresponding reference beers were evaluated by physico-chemical analyses, quantitative chromatographic profiling (HPLC) of the bitter acids, and sensory analysis by a trained taste panel. In the final stage of the project, the new hop technology was implemented succesfully in several medium-sized Flemish breweries through brewing trials on the industrial scale.