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.
