Yeast Management

Question 1

Top cropping yeast

Answer 1

Usually much cleaner and if higher quality

Question 2

Bottom cropping yeast

Answer 2

Contamination with non yeast solids. Sensitive to intensive fermentation practices (eg high gravity brewing) stress can cause mutation.

Question 3

Pure yeast culture

Answer 3

A collection of cells that is of the same stain and free from any other cell type, both yeast and bacteria

Question 4

Yeast master culture

Answer 4

A single pure strain made up of pure cells with identical genomes

Question 5

Handling yeast culture: slope method

Answer 5

-low cost, easy to manage
- contamination risk, risk of genetic variants because cells continue to grow in storage phase, requires subculture every - 2 months.

Question 6

Handling yeast culture: - 80* storage

Answer 6

-less frequent subculturing compared with slope method
- more costly than conventional cold storage.

Question 7

Handling yeast cultures: freeze drying

Answer 7

• stable for at least 1 year, not to expensive
• stressful for yeast, most cells die, drying process can create genetic variants

Question 8

Attributes for a yeast crop

Answer 8

Yeast health, purity, crop that is true to type

Question 9

Yeast propagation

Answer 9

1- yeast bank
2- yeast supply
3- lab propagation
4- brewery propagation

Question 10

Yeast banks

Answer 10

Third party suppliers - dried yeast, ex-brewery pitching yeast, cream yeast, yeast cultures.

In house yeast banks-

Question 11

Handling yeast : freeze drying

Answer 11

• stable for at least 1 year, not to expensive
• stressful for yeast, most cells die, drying process can create genetic variants

Question 12

Handling yeast: liquid nitrogen

Answer 12

-gold standard method, infinite storage, minimal viability loss.
- regular supply of liquid nitrogen and bespoke containers, risk of o2 depletion in confined spaces.

Question 13

Handling yeast cultures:active dried yeast

Answer 13

-bull supply, shelf life of at least 1 year if vacuum sealed.
-shelf life only a few days if seal is broken, limited choice of strains.

Question 14

Laboratory propagation

Answer 14

Day 1- slope working culture
Day 3 - 20ml static culture
Day 6 - 100 ml shake flask
Day 9 - 3L aerated culture with sterile filter
Day 14 - 20L aerated culture with sterile filter

Question 15

Yeast supply

Answer 15

System for ensuring the correct yeast strain in the right quantity and state at the time needed for brewing.

Question 16

How many molecules of alcohol does yeast produce in fermentation for every molecule of military it ferments

Answer 16

Four