Yeast and Fermentation Session
Helmut Kuhnl, Esau & Hueber, Schrobenhausen, Germany
ABSTRACT: Yeast is the single most precious asset that a
brewery owns and our most important operator. Propagation conditions
should ensure that the “best” possible amount of yeast is produced,
which provides an optimal fermentation performance when pitched. Yeast
can survive and grow in the presence or absence of oxygen. In terms of
the yeast cell, its survival and growth is optimal in the presence of
oxygen. Only in an aerobic environment is yeast able to synthesize
unsaturated fatty acids and sterols, which are important components of
the cell membrane and responsible for cell growth. Aerobic propagation
creates most vital cells with a high fermentation power and helps to
suppress potential bacteriological issues. Modern systems use an
aeration device that ensures a uniform distribution of air and a
homogeneous mixture in the yeast suspension. Ideally the design of
propagation vessels should be without intrusions, i.e.,
agitators/stirrers, to accomplish the highest microbiological safety.
Hence observations on prop systems have proved that aeration outside the
propagator with a two-component jet in the loop is the better choice in
terms of hygiene compared to built-in aeration equipment. External
aeration provides further process benefits like the creation of tiny
bubbles, less foaming, homogeneous yeast suspension, perfect air
distribution, and minimal and efficient air flow. The generated vital
cells incorporate high fermentation power and suppress potential
bacteriological issues. Typical process control parameters are the
scheduled time of propagation, temperature, duration of aeration and
frequency of airflow per hour, pitching startout cell count resp, the
residual propagator volume, and wort volume added. In addition to
propagation modern yeast management includes the possibility of crop
yeast revitalization to guarantee a perfect fermentation performance.
This is achieved by circulation with simultaneous aeration of the yeast
before re-pitching, using the same loop as for propagation for removing
the fermentation CO2, homogenization of the crop yeast in the yeast storage/pitching vessel, adding fresh O2
to the crop yeast, and supplying nutrient fluid (wort) if required.
Rigid receipt control systems for yeast propagation are not flexible
enough to run yeast propagation without observation and manual
interaction of an operator. This belongs now to the past. In-line
measurement of cell count and gravity in the loop allow an optimized
adjustment of temperature and aeration rates according to yeast growth
and residual extract with the new yeast propagation manager YPM with the
objective to achieve the best yeast vitality at point of pitching. YPM
is a self-learning fuzzy logic software application acting like an
experienced operator. This virtual expert observes nonstop all the
process parameters, detects trends and reacts, operates 24/7 without
breaks, holiday, and pay slip, releases operators from routine jobs,
increases plant efficiency, flexibility, and reliability, and last but
not least saving money. YPM is the first fully automatic on-line yeast
propagation system.
In 1974 Helmut Kuhnl apprenticed in brewing
and malting at the Spaten-Franziskaner-Bräu Munich before moving on to
study at TU Weihenstephan. He received the Diplombraumeister degree in
1980 and worked in leading sales positions for several process equipment
suppliers. Taking evening classes he obtained his BBA. In 1998 Helmut
joined Esau & Hueber as a sales manager and was significantly
involved in the development of the company into one of the world’s
leading suppliers of yeast management systems during the last decade.
VIEW PRESENTATION 248
