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Consequences of failure

In terms of failure there is a sliding scale of severity for failing to meet best practice recommendations for yeast pitching. Underpitching will result in a sluggish fermentation performance, which - depending on degree - will be readily apparent. If this is due to pitching by mass with no understanding of the contribution of dead yeast, this will result in enhanced cell autolysis and untoward flavours and aromas. A comparable situation can occur running blind with the Aber technology, although increased pitching solids provides an early clue of an increasing dead cell fraction. Although significant overpitching will result in an ageing population of yeast cells, repeated repitching at an elevated rate is unlikely to be a sustainable process. Stretching the maximum generation number is unpredictable and very much specific to the strain in question. The expectation is that this would over time increase the likelihood of sluggish fermentation and selection of variants. Extending yeast pitching from the first brewlength to most or all may be driven by practical considerations or the belief that the approach improves mixing. Whatever the reasoning, extending the pitching profile will result in inconsistency. Here the different batches of yeast will transition from quiescence to growth at different times and (depending how and when oxygen is added) differing availability of oxygen. Competition for oxygen will also not be a ‘level playing field' as the uptake rate increases over the time of exposure (Boulton, 2013). Consequently, subsequent batches of yeast will potentially be out-competed for oxygen by the more voracious appetite of the first pitching of yeast.

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