Finishing and Stability Session
Jean Titze, National University of Ireland, University College Cork, School of Food and Nutritional Science, Cork, Ireland
Co-author(s): Antonie Herrmann, Hochschule Weihenstephan-Triesdorf, Institut für Lebensmitteltechnologie, Freising, Germany; Vladimír Ilberg, Hochschule Weihenstephan-Triesdorf, Fakultät Gartenbau und Lebensmitteltechnologie, Freising, Germany
ABSTRACT: Is the current understanding of chill haze in beer still correct? Brewing science distinguishes between two forms of haze appearance: reversible chill haze and permanent haze. The composition and formation of both forms is described as being identical in the literature, except chill haze is reversible. Further, haze formation in beer is mostly explained by the interaction of protein and polyphenol. The process usually shows an initially reversible bonding between protein and polyphenol, the so called chill haze. This precipitates as an insoluble complex due to catalysis by metal ions or oxygen. These complexes with covalent bonds will not dissolve if heated, and permanent haze appears. A physico-chemical explanatory approach for the reversibility of chill haze is not given by most authors. In general, there are several types of haze predicting tests available. Forcing tests, for example, involve storing beer at elevated temperatures for a certain time (warm days) to speed up the natural aging process. The results of a long-term forcing test over a period of more than 1 year put the existing theory into question. It could be shown that the assumption that an already formed complex could be initially reversible and later irreversible is wrong. A novel physico-chemical explanatory approach could be found, in which the water retention of proteins (hydration) plays an important role. 1) Colloidal haze (permanent haze) formation in beer is purely a matter of a thermal effect, which is the reason for the following two mechanisms: already denatured proteins in beer agglomerate according to collision (DLVO theory) and native proteins start unfolding. After that, they are able to agglomerate. Hence, the basic requirement for haze formation is thermal energy. With every warm day the amount of denatured proteins, which can agglomerate right away, as well as the number of native proteins, which first unfold and then can agglomerate, increase. 2) Chill haze forms due to cool temperatures; the water gets out of the molecule of the nondenatured proteins with a change in the properties of the hydration hull. Two activities are possible: according to diversification of protein hydration the index of refraction of the molecule changes and the particle becomes visible and due to modification of hydration, hydrophobic groups of the protein can interact with themselves or with already denatured proteins and reversibly accumulate with them. Both phenomena are reversible. Independent of the beer aging status, they lead to an increase in haze due to the cold temperature (chill haze).
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.