J. B. Layfield (1), J. H. Hildebrand (1), J. D. SHEPPARD (1); (1) North Carolina State University, Raleigh, NC, U.S.A.
Yeast
Thursday, June 5 - 8:00 a.m.-9:45 a.m.
Level 4, Red Lacquer Ballroom
This mini-review, takes a current look at the numerous factors that
affect overall brewing fitness in brewing yeast strains. Fermentation is
a complex interaction between environmental and microbiological
components. Environmental components are related to the raw materials
and processing conditions used during wort production, while
microbiological components are related to the characteristics of the
yeast used during fermentation and maturation. Quality systems are in
place, in most breweries, to control these components and thus direct
the fermentation; however, the skill, experience, and information
available to the brewer ultimately determines the outcome of the beer
and allows the brewer to face sudden, unexplainable changes in flavor,
aroma, and/or fermentation performance. Environmental components are
generally fixed, and tightly controlled. Variations arise as a function
of raw ingredient quality, which like most raw agricultural commodities,
may have some inherent, uncontrollable variability. Generally,
microbiological components are related to yeast strain, purity,
propagation/handling conditions, number of times re-pitched, cell
number/pitching rate, viability, and vitality. The difficulty with
microbiological components is that data produced from many of the
methods for assessing purity, cell number/pitching rate, and viability
and vitality can be problematic. The presentation of the data can also
be challenging, as some of the words and terms used to describe
microbiological attributes may have different meanings depending on the
audience. This mini-review seeks to differentiate between viability and
vitality, it discusses influencing factors, and details current best
methods and means of analysis, all in context for the brewing industry.
We also seek to clarify differences between cell age, re-pitch number,
and the affect these yeast attributes have on overall brewing fitness
and fermentation performance.
John Sheppard is a professor in the Department of Food,
Bioprocessing, and Nutrition Sciences at North Carolina State
University. He received a Ph.D. degree in chemical engineering from
McGill University in Montreal in 1989 and an MBA from ESCP in Paris in
1997. John currently teaches biopharmaceutical production, cGMP
fermentation operations, and process validation in the Biomanufacturing
Training and Education Center (BTEC) at NCSU. Previously, he taught as a
professor in the Department of Bioresource Engineering at McGill
University. His research is focused on the development and control of
fermentation and cell culture processes applied to brewing and
biopharmaceuticals. He has authored or coauthored over 45 peer-reviewed
papers and holds three patents. He is a registered P.E. and consults for
companies within the biotechnology sector on issues related to
fermentation process optimization and scale-up.
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