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64. Increasing bitter substance yield by recycling hot trub and yeast washing solution

F. Pereira (1), T. KUNZ (1), M. Marinoff (1), F. J. Methner (1); (1) Technische Universität Berlin, Berlin, Germany


Bitter substance utilization during conventional beer production is considerably low. It is generally known that the major losses of BU occur during wort boiling and fermentation. Recent studies gave a deeper insight into the losses of bitterness during different process steps and the investigation of specific influencing factors like pH and iron content in model solutions. Furthermore, the pH influences on the precipitation of hop acids was investigated in wort, with and without yeast addition. The findings were applied to develop a new procedure to improve the bitter yield by recovery from hot break and yeast washing solution. The results demonstrate that reversible, pH-dependent hop acid complexes, including iron ions, are mainly responsible for the loss of BU during wort boiling and fermentation. The bitter substances precipitate with the hot break due to complexation with iron ions and during the first days of fermentation due to the pH drop caused by yeast. The achieved knowledge about the reversibility of pH-dependent precipitation can be used to improve the bitter yield by recovering the hop acids from the hot break and yeast washing solution under specific alkaline conditions and high temperatures. The usually applied method of recirculating the hot break to the lautering process should be reconsidered, since the new method leads to a higher bitter yield and also separates the prooxidative acting iron ions, resulting in better oxidative beer stability. Also later or incremental dosage regimes could become more popular since nonutilized alpha-acids can be recovered.

After qualifying as a certified technician in preservation engineering (1991–1993), Thomas Kunz completed his basic studies in chemistry at the University of Applied Sciences, Isny (1994–1995) and his basic studies in food chemistry at Wuppertal University (1995–1998), before studying food technology at the University of Applied Sciences, Trier (1998–2002). After graduating, he worked as a chartered engineer in the area of ESR spectroscopy at the Institute of Bio Physics at Saarland University (2002–2004). Since 2005, he has been employed as a Ph.D. student and scientific assistant in the Department of Biotechnology, Chair of Brewing Sciences, Berlin Institute of Technology (Technische Universität Berlin). As head of the laboratory since 2009 his main research focus lies in analyzing the influences of brewing process stages, filter aids, stabilizing or fining agents, and specific beer ingredients on radical reaction mechanisms and the oxidative stability of beer or other beverages using ESR spectroscopy and GC-MS. Another part of his research is the influence of oxygen during brewing and oxygen permeation through a wide range of different packaging materials during storage.

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