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Generation number

The number of times yeast is cycled between fermentations comes up from various perspectives throughout this chapter. Today, a more proactive management (10 to as low as 5 or fewer cycles) has succeeded the laissez-faire approach of 20 or more generations in the past. The drivers for this change are not entirely clear. Whilst hygiene and yeast handling are arguably better than in the past, awareness of genetic change is more pronounced and may contribute to this. A good and quantified explanation for this is reported by Stewart (2015). Over a period of 15 years in a North American brewing group, average wort gravities increased from 12 to 14 to 16 and finally to 18° Plato. In turn this was accompanied by yeast generation numbers reducing from > 20 to 16 to 12 and finally to 8 cycles (Stewart, 2015). These changes were introduced over time to avoid ‘fermentation difficulties' in rate and/or extent. Another study (Jenkins et al., 2003) reports for a (then) major UK brewer that company policy for maximum generation number of four production yeasts ranged from 10 (two strains) to eight and five.

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