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

Yeast reproduction in high-gravity wort, producing more alcohol

Answer

The conversion of maltose to glucose by yeast enzymes during fermentation

Answer

Yeast adaptation to high-alcohol environments through cell wall thickening

Question 2

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

Accepted Answer

Diacetyl

Answer

Acetaldehyde

Answer

Dimethyl sulfide (DMS)

Answer

Isoamyl acetate

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

0.5 million cells/mL/°Plato

Answer

5 million cells/mL/°Plato

Answer

10 million cells/mL/°Plato

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

Top-fermenting yeasts produce more alcohol than bottom-fermenting yeasts

Answer

Bottom-fermenting yeasts produce more esters and fruity flavors

Answer

Top-fermenting yeasts cannot ferment maltotriose

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

To initiate mashing enzymes at a controlled temperature

Answer

To naturally pre-carbonate the wort before fermentation

Answer

To measure wort gravity and fermentability in advance

Question 6

Which nutrient is considered most critical for yeast health and fermentation vigor in wort?

Accepted Answer

Free Amino Nitrogen (FAN)

Answer

Magnesium

Answer

Zinc

Answer

Calcium

Question 7

What is the purpose of a diacetyl rest in lager production?

Accepted Answer

To raise the fermenting beer's temperature near the end of fermentation so yeast can reabsorb diacetyl

Answer

To halt fermentation at a target final gravity

Answer

To clarify the beer by encouraging yeast to flocculate and drop

Answer

To add flavor adjuncts to the fermenter during active fermentation