Leo Chan (1),
Dmitry Kuksin (1), Jaime Schier (2), Joseph Thomas (2); (1) Nexcelom
Bioscience, Lawrence, MA, U.S.A.; (2) Harpoon Brewery, Boston, MA,
Yeast, Fermentation, and Microbiology
Flash pasteurization has traditionally been deployed in the brewing
industry to stabilize beer by reducing the number of beer spoilage
organisms per mL, ensuring a long and stable shelf life free from
defective flavors and aromas created by the likes of L. brevis and P. damnosus.
As innovative new beers from the craft segment arrive, new challenges
to beer stability sometimes manifest. In the case of beers containing
high levels of residual fermentable sugar, a new contaminant
microorganism must be accounted for in the form of the brewer’s own
yeast that conducted the initial fermentation of the beer. Some craft
brewers are turning to pasteurization to reduce viable yeast counts. A
novel method of verifying successful reduction of viable yeast cells in
final packages of beer was developed that provides the brewer with
real-time validation of the effectiveness of both pasteurization
operations as well as sanitary bottle-, can-, or keg-filling operations.
In order to determine if the beer product is ready for bottling after
flash pasteurization, yeast viability is quickly measured using the
Cellometer image cytometer. First, 50 mL of the product is collected,
and the sample is concentrated to approximately 250 µL. The yeast cells
are then stained using the yeast dilution buffer and acridine
orange/propidium iodide fluorescent stains to determine live/dead cell
count and viability. Since the yeast cell concentration is low, multiple
samples are analyzed to ensure the results are statistically accurate.
The ability to quickly measure yeast viability enables a more efficient
process for QC and manufacturing, which can further improve the quality
and throughput of the beer products.
Leo Chan currently serves as the technology R&D manager at
Nexcelom Bioscience LLC, Lawrence, MA. His research involves the
development of instruments and applications for the Cellometer image
cytometry system for detection and analysis of yeasts used in the
brewing and biofuel industries. He is a member of the Master Brewers
Association of the Americas and American Society for Brewing Chemists.
He received his B.S., M.S., and Ph.D. degrees in electrical and computer
engineering from the University of Illinois at Urbana-Champaign