Microbiology Session
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.
VIEW PRESENTATION 167
