banner 6. Practical experiences with an automated yeast cell counter using methylene blue in breweries

K. M. Thomson (1), J. P. CARVELL (1), A. R. Bhat (1) (1) Aber Instruments Ltd., Aberystwyth, U.K.

Technical Session 2 - Industrial Yeast Management
Sunday, June 14
2:00–3:15 p.m.
Fiesta 3,4,6,8

Automation in breweries has always been sought after, especially with respect to cell counting procedures that reduce errors associated with manual counting and inter-operator variability. Along with being expensive, the fluorescent dyes used in most automated cell counters pose greater hazards and health and safety concerns. In addition, viability estimation using fluorescent dyes tends to be a two step process, or require dual staining, as opposed to a simple one-step process with classical stains such as methylene blue and methylene violet. Therefore, “the gold standard” methylene blue dye exclusion method is still favored in the industry. In this paper, we report the performance, functioning, and benefits of an automated cell counter (the Aber Countstar, Aber Instruments, U.K.) that analyzes yeast viability using the methylene blue dye exclusion method for brewer’s yeast. Previous work had demonstrated the instrument’s accuracy and improved consistency with baker’s yeast when compared to manual counts. In this study, the Countstar was tested across a selection of industrial dried lager and ale yeasts. In addition, bottled wheat beer samples containing trub, that can pose a challenging background, were tested using the Countstar. Inter-operator variability was assessed using automated and manual methods, where cell concentrations and viabilities were recorded by four different operators using both procedures and compared for consistency. All results from the Countstar were compared to manual cell counts using the hemacytometer. Variables were kept to a minimum using the two techniques, since both methods use bright-field microscopy and methylene blue. The study also includes extensive tests performed by The Boston Beer Company (USA), where yeast from different processes in the brewery, namely fermentation, propagation, and yeast storage was analyzed and compared using the automated and manual methods. The Countstar readings matched well with hemacytometer counts for various active dry yeasts (e.g. R2 = 0.991), through a range of concentrations with readings. However, some active dry strains did not correlate well, as with one ale yeast tested (R2 = 0.537), although this was due to high variation in the manual cell counts (R2 = 0.993 Countstar; 0.292 manual). A simple evaluation of some parameters in the Countstar software improved accuracy of measuring the wheat beer samples with interfering trub particles in association with manual assessments (R2 = 0.938). The automated Countstar reduced inter-operator errors among four operators considerably, a major hindrance with manual analyses. The tests performed at The Boston Beer Company demonstrated that the automated counter can be used successfully with both lager and ale yeast, throughout various stages of the brewing process and highlighted the instrument’s ease of use and consistency across the brewery.

John Carvell is the managing director of Aber Instruments Ltd. and is based out of Aberystwyth, UK. He is a graduate in biochemistry and received his Ph.D. degree at Newcastle University, UK. John has held roles as production manager at a bakers yeast manufacturer and senior sale roles within engineering contractors before joining Aber Instruments Ltd. in 1994. With the business over 90% export and split between both the brewing and biotechnology industries, he spends a large proportion of his time visiting companies involved in diverse range of applications for on-line biomass monitoring. John has presented papers and posters at many of the major biopharma and brewing conferences including the SIM (Society of Industrial Biotechnology), RAFT (Recent Advances in Fermentation Technology), ACS, and both the ASBC (American Society of Brewing Chemists)and MBBA (Master Brewers of America Association) annual meetings. He has also published various papers including a major review in cytotechnology.

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