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Consequences of failure

Propagation of brewery yeast sets the tone of subsequent fermentations generation by generation. The ‘traditional' propagation approach is without focus on cell yield. The addition of oxygen to the propagator via the periodic bubbling of air via a ‘lance' achieved little if any gas transfer so that propagation was effectively anaerobic. Yields were poor (ca 50 x 106/ml) and little attempt was made to match the required yeast pitching rate. At best the fermentation vessel would be partly filled and then topped up some days later with fresh wort. Typically, the performance of such yeast would be woeful, such that the fermentation charts tracking gravity fall would extend from the usual single page to two or even three pages. Such extended fermentations result in poor-quality yeast of compromised viability. On pitching on, this extends fermentation vessel cycle times, and at best a number of fermentation generations are required before the yeast achieves the required and repeatable cycle times and associated product quality.

The above is the readily visual ‘tip of the iceberg'. Cutting corners in terms of hygiene or step-up volumes can add further woe in terms of product

Table 3.3 Yeast propagation from laboratory to the brewery

Step

Comments

Laboratory

Yeast on agar slope

1

From ‘yeast supply’

  • 2 x 10 ml - static - 24 hours at 25°C
  • 1

All yeast recovered from slope

  • 2 x 100 ml - shaken - 72 hours at 25°C
  • 1

Shake flasks in an orbital incubator

3 l - constant aeration - 72 hours at 25°C 1 1 1

Shake flasks in an orbital incubator - entry of ‘liquid culture’ from a supplier

20 l - constant aeration - 72 hours at 25°C 1

‘Carlsberg flask’ modified to improve gas transfer or entry of ‘liquid culture’ from a supplier

Plant

  • 1
  • 8 hl - oxygenation - 30 hours at 25°C
  • 1

13 hl seed vessel

  • 140 hl - oxygenation - 30 hours at 25°C
  • 1

220 hl propagator

1500 hl, 15°P wort

1600 hl FV, pitched at 15 x 106 viable cells/ml

quality and consistency, which is potentially amplified further with successive generations of use.

 
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