Master Brewer Certification Yeast Biology & Fermentation Science 2

Question 1

What is autolysis in brewing yeast, and what sensory impact does it have on beer?

Accepted Answer

The self-destruction of stressed or aged yeast cells, releasing meaty, rubbery, or soapy off-flavors

Answer

Autolysis occurs when yeast enzymes digest their own cell contents, releasing unpleasant compounds like fatty acids and proteases into the beer.

Question 2

Which fermentation byproduct causes a buttery or butterscotch off-flavor in beer and must be reduced before packaging?

Accepted Answer

Diacetyl

Answer

Diacetyl is a vicinal diketone (VDK) produced during yeast growth that must be reabsorbed by healthy yeast at the end of fermentation.

Question 3

What is the standard pitching rate recommended for an ale wort with an original gravity of 1.050?

Accepted Answer

1 million cells/mL/°Plato

Answer

The widely accepted standard pitching rate for ales is 1 million viable cells per mL per degree Plato of original gravity.

Question 4

What is the primary distinguishing characteristic between top-fermenting ale yeast and bottom-fermenting lager yeast?

Accepted Answer

Ale yeasts ferment at warmer temperatures and rise to the surface; lager yeasts ferment cooler and settle to the bottom

Answer

The key difference is fermentation temperature and flocculation behavior — ale yeasts (S. cerevisiae) are warm-tolerant top-croppers; lager yeasts (S. pastorianus) are cold-adapted bottom settlers.

Question 5

What is the purpose of preparing a yeast starter before brew day?

Accepted Answer

To propagate and increase the quantity of viable yeast cells to achieve a proper pitching rate

Answer

A starter grows a larger, healthier yeast population from a smaller initial culture, ensuring enough cells for a healthy pitch without underpitching.

Master Brewer Certification Practice Test

Master Brewer Certification Practice Test

Master Brewer Certification Yeast Biology & Fermentation Science 2