Evaluation of pre-isomerized hop extracts and their influence on the long-term stability of beer by using a charge titration method

Technical Session 20: Finishing and Stability Session
Jean Titze, National University of Ireland, University College Cork, School of Food and Nutritional Science, Cork, Ireland
Co-author(s): Jörg Kaspar, Technische Universität Berlin, Institute of Technology, Chair of Brewing Sciences, Berlin, Germany; Pedro Oliveira, National University of Ireland, University College Cork, School of Food and Nutritional Science, Cork, Ireland; Christina Schönberger, Barth-Haas Group, Barth Innovations, Joh. Barth und Sohn, Nuremberg, Germany; Vladimír Ilberg, Hochschule Weihenstephan-Triesdorf, Fakultät Gartenbau und Lebensmitteltechnologie, Freising, Germany; Elke K. Arendt, National University of Ireland, University College Cork, School of Food and Nutritional Science, Cork, Ireland

ABSTRACT: Assuring a constant beer quality is one of the biggest challenges in the brewing industry. One important parameter is the physico-chemical stability of the product. This is the resistance of filtered beer against haze formation. One of the main ingredients of beer is hops. Hop bitter acids are the major bitter compounds in beer. They contribute to more than 85% of the overall bitterness. Humulones (alpha-acids) that are present in hops undergo an isomerization reaction to isohumulones (iso-alpha-acids) after thermal treatment. Usually the yield of iso-alpha-acids derived from the dosed hops is not more than 30%. This low yield is caused by numerous factors. Therefore, the use of pre-isomerized hop products such as isomerized kettle extract is a possible approach to achieve higher yields (>50%). Besides the reduction of losses, downstream products are used to produce light stable beers or to improve foam stability. The question remains, do the different downstream products have a positive effect on the long-term stability of filtered beer? With the help of a wort granulate a standardized beer was brewed. After fermentation and maturation different pre-isomerized hop extracts containing purely iso-alpha-acids (IAA), rhoiso-alpha-acids (RIAA) and tetrahydroiso-alpha-acids (THIAA), as well as a mixture of RIAA and THIAA were added just before the final filtration. The dosage of acids was adjusted to the amounts usually used in commercial breweries. To prevent the unhopped wort from boiling over (especially at the beginning of boiling), as well as to avoid an infection with unwanted microorganisms from the wort and/or green beer, beta-extract was added to the pre-boiled wort. As a comparison a traditionally hopped beer with hop pellets was brewed using the same wort granulate to determine the influence of the polyphenol fractions on haze stability. To predict the time until haze becomes visible, two methods were used: 1) determination of the particle surface charge with titrimetric analysis (charge titration method), and 2) a modified forcing test performed according to MEBAK (artificial aging). With the first method the prediction of haze formation was already possible in the fresh bottled beer using the calculation of a stability factor. When performing the forcing test long-term stability was represented by the haze increase after a certain time of artificial aging. Both methods revealed the same results. While the beer hopped with THIAA showed the smallest haze increase, which means the best long-term stability, the beers with IAA or combination of THIAA and RIAA were less stable. In between was the beer with RIAA. However, all the beers with pre-isomerized acids showed a significantly higher physico-chemical stability than the traditionally hopped beer. It should be noted that long-term stability is only one parameter of beer quality. Overall quality in terms of flavor was not investigated.

Jean Titze studied the technology and biotechnology of food at the Technical University of Munich, as well as food and feed law at the Academy of Food Law, Philipps-University of Marburg. He worked several years as a brewery consultant for the Research Center Weihenstephan for Brewing and Food Quality and later as a senior consultant for Deloitte, focusing on the food and beverage industries. Since March 2011 he has been a senior research scientist at UCC, focusing his research on colloidal chemistry and particle analysis. For his research in the area of colloid science he received the 2011 Research Award from the German Brewing Industry. Since winter term 2011/2012 he is also a lecturer for food law at the University of Applied Science Weihenstephan-Triesdorf.