Thomas Kunz, Technische Universität Berlin, Department of Biotechnology, Chair of Brewing Sciences, Berlin, Germany
Co-author(s): Cecilia Cruz Palma and Frank-Jürgen Methner, Technische Universität Berlin, Department of Biotechnology, Chair of Brewing Sciences, Berlin, Germany
ABSTRACT: To assure high fermentation quality it is necessary to get as much information as possible on the actual yeast condition. To achieve uniform fermentation two major factors have to be taken into account: yeast cell concentration and its viability. Since it is not possible to attain 100% viable cells, the relationship between dead and living yeast cells is a very important factor needed to adjust the pitching rate. Furthermore information about the influence of different fermentation parameters such as extract composition, temperature, pressure, etc. can be gathered when monitoring the yeast cells during fermentation. Several methods have been developed to determine and analyze cell number and viability using a minimum amount of effort. The aim of this study was to compare a new fluorescence microscope detection system, an automatic cell viability counter (Cellometer M10 - PeQlab), with the established Nucleocounter (Chemometec) using the fluorescent dye propidium iodide in the chamber and the traditional Thoma counting chamber using methylene blue. The different cell counting systems were evaluated according to the following parameters to support brewers in an attempt to find the best qualified method for yeast management, e.g., accuracy, variance of distribution, handling, expenditure of time, costs. All three methods are suitable for determining the total yeast cell concentration and the viability. Viability determination using fluorescence dyes is easier to deal with as it penetrates the cell instantly and stays unchanged. Methylene blue stained cells increase with the incubation time leading to a distortion in detected viability. The Nucleocounter and Cellometer present advantages against the Thoma chamber in ease of handling and fast measurement times. The new Cellometer demonstrates high sensitivity and accuracy when performing a visual examination. Additionally, the best detection of dead cells and viability was demonstrated. Overall it can be said that the new Cellometer is a qualified, accurate method for yeast counting and viability determination. It has the big advantage that the parameters for each yeast strain can be specifically optimized leading to more accurate detection. This makes it possible to analyze yeast strains with small shapes such as Ludwigii species and yeast mixtures in more detail. The high investment cost disadvantage, in comparison to the Nucleocounter, is compensated for by the extreme lower cost of each measurement. Furthermore only one measurement per sample is needed for determining both the total cell concentration and the viability.
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 January 2005, he has been employed as a Ph.D. student at the Research Institute of Brewing Sciences, Berlin Institute of Technology (Technische Universität Berlin). His main research focus lies in analyzing radical reaction mechanisms in beer and other beverages using ESR spectroscopy.