Optimisation of High Gravity and Diet Beer Production in a German Brewery by Flow Cytometry

Increasing the quantity of beer production without diminishing the quality of the product is a key concern of the beer producing industry. Modifications to the brewery's equipment and settings are the most commonly used methods to improve the brewing process, while the supreme importance of the physiological state of the beer producing organisms, the yeast cells, for the productivity of the brewing process is often poorly recognised. The work described here was designed to optimise two processes: the inoculation regime used to produce high gravity bottom-fermenting beer, and the production of high quality diet beer. To achieve these aims, flow cytometry was used to follow changes in the distribution of DNA, neutral lipid and 3β-hydroxsterol contents in Saccharomyces carlsbergensis strains during inoculation, fermentation and storage. This allowed potential time-saving alterations in the process to be identified. Double staining techniques proved that vigorous fermentative activity and long-term survival capacity during main and secondary fermentation requires intense multiplication of the yeast cells during inoculation. The production of high gravity beer was then enhanced by altering the schedule of the wort additions, and thus increasing the yeast's activities related to multiplication. To produce diet beer, oligosaccharides that remain after the standard brewing process are degraded by adding small amounts of wort, usually during secondary fermentation. However, during this period of fermentation the physiological activity of the yeast cells is hampered by low carbon and high ethanol concentrations. Adding small batches of wort at carefully defined time points and in optimised amounts, even during the main fermentation, improves the physiological state of the yeast cells and rapidly decreases the carbon concentration within the fermentation tank. Both of these factors help to promote quick fermentation to a high quality diet beer. Thus, the flow cytometric investigations provided a reliable basis for identifying effective means of improving the process regime for brewing both of these products.