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.
VIEW PRESENTATION 137
