S. HENKE (1), K. Sommer (1); (1) Technische Universität München - Chair of Process Engineering of Disperse Systems, Freising/Weihenstephan, Germany

Poster

The major purpose of mashing is starch degradation to fermentable sugars. The enzymes involved in this process and their temperature and pH optima are well-known. The reactions of amylases with the major starch polysaccharides amylose and amylopectin are considered to be very fast. Nevertheless mashing is a time- and energy-consuming process step in the brewhouse. The question arises, why are intensive mashing procedures with long rests necessary, when the enzyme reactions are said to be very fast? For this reason the aim of this work is to look in more detail at the reactions that have to take place before enzymes are able to attack. The most important one is the phase transition of starch called gelatinization. Gelatinization is a temperature dependent process that provokes hydration of the starch polysaccharides, resulting in a loss of crystallinity of the starch granules. Gelatinization is a comprehensive term for several reactions starch undergoes in parallel in excess water at higher temperatures. In particular, these are swelling of starch granules, water uptake, and amylose leaching. During mashing all of these reactions superimpose themselves and are overlaid with beginning enzyme reactions. This requires a sophisticated interpretation of experimental results, because an unequivocal assignment to the single reaction is often impossible. In this work each part of the gelatinization reaction was investigated separately and decoupled from enzyme reactions by the use of enzyme-free barley starch. The starch particle size development during swelling was detected by laser diffraction and light microscopy, respectively. The speed of the reaction, as well as the resulting particle size, depend on time and temperature. The amount of water entering the starch granule could be measured by an indirect photometric method. The results showed that swelling of the starch granules is much faster than the water uptake. A complete gelatinization of starch granules results in disintegration and bursting of the granules. The literature indicates that complete gelatinization only takes place when amylose, located in the amorphous regions of the granule, has left the granule. This extraction process of amylose was measured under variations of the process parameters temperature, starch particle size, and agitation speed. As all mentioned sub-processes of gelatinization are problems of mass transfer, a mathematical description is applied based on the procedural basics of diffusive and convective mass transfer. This work tries to make a contribution to a better understanding of the single reactions that take place during gelatinization of starch and the process parameters that have an influence. This knowledge may be used to derive optimization potentials of the process. This research project was supported by the German Ministry of Economics and Technology (via AiF) and the FEI (Forschungskreis der Ernährungsindustrie e.V., Bonn). Project AiF 16542 N.

Simon Henke graduated from Technische Universität München in 2009 as a degreed engineer in brewing science and beverage technology. In 2010 he started his work at the Chair of Process Engineering of Disperse Systems, Technische Universität München, as a research associate. His fields of activity are mass transport phenomena and procedural aspects of the mashing process. Simon is involved in student education in thermal and mechanical process engineering. He is responsible for the laboratory for wet and dry particle size analysis.