Brewing Yeast
Fermentation Performance

Preface to the second edition

Controlling the impact of stress on brewing biomass, predicting yeast activity and
ensuring consistent fermentation performance through successive fermentations
remain areas of active interest for the brewing industry.
To be able to control and perhaps even manipulate yeast activity, it is necessary to
identify factors that affect its functionality during fermentation. Genetic stability and
integrity are crucial to maintaining predictable performance. The brewing yeast
genome is inherently unstable, leading to the formation of nuclear and mitochondrial
variants during yeast handling and fermentation. Although recent molecular innovations
may allow rapid detection of such occurrences, the causes and nature of the DNA
damage remain to be elucidated.
During handling and fermentation the yeast is subjected to a rapidly changing
environment. There are many stresses to be considered, including physical stresses
such as shear, cold shock and hydrostatic pressure, and those created by the yeast’s
own biochemical activity such as oxidative stress, nutrient limitation, anaerobiosis,
osmotic stress, low pH, excess carbon dioxide and the formation of toxic metabolites.
In addition, wort composition is a critical determinant of yeast performance and final
product quality. Batch-to-batch changes in component ratios inevitably contribute to
the variability in performance exhibited by a given slurry, yet few extensive studies
have been conducted in this area. This very variability in both wort composition and
yeast quality is reflected in final beer quality and in particular beer flavour. The role
of the yeast cell in flavour attributes is therefore dependent on both intrinsic and
extrinsic factors.


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