Martina Gastl, Lehrstuhl für Brau- und Getränketechnologie, Freising, Germany
Co-author(s): Elisabeth Wiesen, Barth Innovations, Nürnberg, Germany; Thomas Becker, Lehrstuhl für Brau- und Getränketechnologie, Freising, Germany
ABSTRACT: Turbidity provides the consumer’s first visual impression of beer quality. Consumers expect a filtered beer to be a clear, bright, non-hazy product that remains so during its shelf life. Hazy products are often regarded as defective and perhaps even potentially harmful. Therefore, controlling haze formation is an important problem in beer production. For breweries not only costs from rejected turbid beers and therefore an “image problem” arise, but also increased costs due to the higher use of filter aids have to be considered. It is well known, that beer is a complex mixture of over 450 constituents. In addition, it contains macromolecules such as proteins, nucleic acids, polysaccharides, and lipids. Proteins influence the entire brewing process with regard to enzymes, which degrade starch, beta-glucans, and proteins. Protein-protein linkages stabilize foam and are responsible for the mouthfeel and flavor stability of beer. Together with polyphenols, proteins are thought to cause haze formation. With this complexity, problems in processability are as various as the constituents. Several substances in beer are responsible for haze formation. Organic compounds such as proteins, polyphenols, and carbohydrates (alpha- and beta-glucans) are known to form haze. In addition, inorganic particles such as filter aids and label residues can cause increased turbidity. In the brewery it is necessary to have methods not only to identify the haze, but also to determine the source of the haze formation. A simple, reproducible, and low cost analysis procedure that can be carried out with basic laboratory equipment demonstrates that the source of haze particles in beer (raw material, yeast, etc.) can easily be determined and technological factors during the brewing process of haze formation can be monitored step by step. This study presents an overview of several research studies (haze formation and haze identification), as well as analytical methods for haze formation, protein analysis, and haze identification, including dyeing methods, microscopic analyses, and size exclusion chromatography.
Martina Gastl apprenticed as a brewer and maltster from 1994 to 1996 in Klosterbrauerei Andechs, Germany. She studied brewing and beverage technology at the Technische Universität München-Weihenstephan, Germany. She graduated as an engineer in 2002. From 2002 until 2006 she completed her Ph.D. concerning the “Technological Influence on Lipid Degradation in Terms of Improvement of Beer Flavor Stability.” She is currently assistant professor and head of the laboratory, as well as the raw material and beverage design research group, at the Lehrstuhl für Brau- und Getränketechnologie in Weihenstephan. Since 2008 she has been working on her post-doctoral lecture qualification. Her research interests involve characterization and interaction of flavor active taste and aroma compounds in cereal-based beverages influencing beverage harmony.