Lesson 8 - Yeast Management
This lesson will explore the methods that are used to measure yeast’s concentration and to assess its health. We will then go on to describe how this knowledge underpins the methods used to store and handle yeast in the brewery.
Point of Reflection – Reconvene
Welcome back! So, what were your thoughts?
Considering the numbers given above:
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We pitched at 10 million viable cells /mL, so that is 10 x 106 cells / mL
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The viability was 90% so the total number of cells pitched /ml was:
10 x 106 x 100/90 = 11.1 x 106 /mL; therefore, 1.1 x 106 /mL dead cells
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At the end of fermentation, we had 95% viability, with 60 x 106 viable cells /mL
So, 60 x 106 x 100/95 = 63.2 x 106 total; 3.2 x 106 dead cells
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This means that at the end of fermentation we had:
(3.2 – 1.1) = 2.1 x 106 /mL more dead cells than at pitch
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The wort volume was 100 hL and looking at total numbers of cells, at the end of fermentation we had:
(2.1 x 106 x 1000 x 100 x 100) = 2.1 x 1013 more dead cells in total
This is an enormous number! So enormous that it is quite difficult to comprehend. The real number is probably even bigger because some of the dead cells will have lysed (split open) and so will not have been counted at all.
It is hard to imagine that these dead cells do not have some impact on the beer, maybe good or bad.