Process & Ingredients: Yeast and Fermentation

Question 1

What describes a yeast strain’s ability to decrease the OG of wort upon fermentation?

Answer 1

Apparent attenuation

Question 2

What is the ability of the yeast to settle out of the beer upon completion of fermentation?

Answer 2

Flocculation

Question 3

What are the three (3) environmental conditions that differ with each yeast type and strain?

Answer 3

Alcohol tolerance, oxygen requirements, and sensitivity to wort composition (sugar).

Question 4

What describes how well a yeast strain will continue to ferment as the alcohol concentration increases during fermentation?

Answer 4

Alcohol tolerance

Question 5

Name three (3) of the by-products produced by yeast.

Answer 5

Esters, fusel alcohols, diacetyl, and sulfur compounds.

Question 6

Ethyl-acetate, isoamylacetate and ethyl-hexanoate are common forms of these, that impart a fruity, sweet aroma in beer.

Answer 6

Esters

Question 7

Diacetyl, a yeast by-product, produces a buttery note in beers if what occurs?

Answer 7

Premature removal of yeast.

Question 8

Which yeast work best in the 55-75 degree range, with apparent attenuation ranging from 69-80%?

Answer 8

Ale yeast

Question 9

Which yeast work best in 46-56 degrees, with apparent attenuation ranging from 67-77%?

Answer 9

Lager yeast

Question 10

Frohberg is a type of lager yeast. What is it also known as? This yeast ferments quickly, and does not flocculate as well.

Answer 10

Dusty or “powdery”

Question 11

This type of lager yeast flocculate more readily.

Answer 11

Saaz (also known as S.U. or “break”)

Question 12

What is used in the production of Berliner Weiss style with an intense lactic sourness?

Answer 12

Bacteria (lactobacillus delbruckii)

Question 13

Yeasts of Brettanomyces genus generate sourness for which beer style?

Answer 13

Lambics

Question 14

What are the five (5) phases of growth in the yeast life cycle?

Answer 14

Lag, Accelerating, Exponential, Decelerating, and Stationary

Question 15

What phase of growth is when the yeast adapts to the new environment and begins to make enzymes?

Answer 15

Lag phase (or latent phase)

Question 16

What phase of growth is when the yeast starts to divide by budding to reach the optimal density necessary for true fermentation?

Answer 16

Accelerating phase (or low krausen phase)

Question 17

What phase of growth is when the growth rate is constant at the maximum rate? The yeast have completely adapted to the condition of the wort.

Answer 17

Exponential phase (or log phase, or high krausen phase)

Question 18

What phase of growth is marked by the growth rate gradually decreasing?

Answer 18

Deceleration phase (or late krausen phase)

Question 19

What is the final phase of growth, where the number of yeast cells remains approx. constant?

Answer 19

Stationary phase

Question 20

A common method of adding fresh yeast during beer packaging, where fresh yeast starter and glulcose are added.

Answer 20

Bottle conditioning

Question 21

Bottle conditioning is typically done for which beer sytle?

Answer 21

Trappist-style Belgian ales

Question 22

A common method of adding fresh yeast during packaging, where freshly fermenting beer is added.

Answer 22

Krausening

Question 23

Krausening is typically done for which beer style?

Answer 23

German lagers

Question 24

What fermentation by-product can be controlled by choice of yeast strain, wort gravity, wort aeration, and fermentation temperature?

Answer 24

Esters

Question 25

What fermentation by-product is produced by certain wild yeast strains?

Answer 25

Phenols

Question 26

These fermentation by-products are metabolized from amino acids. Their production increases as the fermentation temperature increases, and they also increase with wort gravity.

Answer 26

Fusel alcohols

Question 27

This fermentation by-product is more likely to occur in higher fermentation temperatures, and is highly dependent on the length of yeast’s contact with beer.

Answer 27

Diacetyl