Yeast/Fermentation

Question 1

What is the ale yeast called?

Answer 1

Saccharomyces cerevisiae

Question 2

What is the lager yeast called?

Answer 2

Saccharomyces pastorianus

Question 3

What is the differene between anaerobic and anoxic?

Answer 3

Anaerobic = metabolic process without oxygen

Anoxic = environment without oxygen

Question 4

What two yeast species combined to form S. pastorianus?

Answer 4

S. cerevisiae and S. eubayanus

Question 5

What are the 3 distinct traits of lager yeast?

Answer 5

1. Bottom fermenting
2. Utilizes melibiose
3. Cannot grow at 37°C

Question 6

What are the 3 distinct traits of ale yeast?

Answer 6

1. Top fermenting
2. Cannot utilize melibiose
3. Can grow at 37°C

Question 7

What family of fungi does brewing yeast belong to?

Answer 7

Ascomycota

Question 8

What are the designations for the 2 haploids that sexually reproduce to form the yeast dipolid?

Answer 8

“a” haploid and “alpha” haploid

Question 9

Where is the DNA stored in the yeast cell?

Answer 9

The nucleus

Question 10

How many chromosones does brewing yeast contain?

Answer 10

16

Question 11

What are yeast cell membranes composed of?

Answer 11

Phospholipids

They have a polar head and nonpolar head to form the cell membrane

Question 12

What are the 5 methods of tranport through the yeast cell membrane?

Answer 12

1. Facilitated diffusion
2. Active transport
3. Symport
4. Antiport
5. Passive diffusion

Question 13

What effect does ethanol have on yeast cell membranes?

Answer 13

• Denatures proteins
• Displaces water of hydration
• Disrupts membranes by acidifying cytoplasm

Question 14

What is the Lectin-based Flocculation Hypothesis?

Answer 14

• Zymolectin proteins in the outer cell walls bind to mannose sugars in the cell walls of nearby yeast
• Ca is essential for binding

Question 15

What is the maximum number of bud scars that a yeast cell can have?

Answer 15

~40 scars

Question 16

What is the significance of the p^- mutant?

Answer 16

It is a petite mutant that contains mutations in the mtDNA genome

Question 17

What is the significance of the p⁰ mutant?

Answer 17

It is a petite mutant that has lost mtDNA genome

Question 18

What is the purpose of the vacuole in the yeast cell?

Answer 18

• Provides dynamic storage
• Breaks down proteins

Question 19

What order will yeast use the following sugars?

Maltose, maltotriose, glucose, dextrin

Answer 19

1. Glucose
2. Maltose
3. Maltotriose

Dextrin is never used by the yeast cell

Question 20

What is the process called that transforms amino acids into keto acids?

Answer 20

Trans-amination

Question 21

What is the process called that transforms glucose into pyruvate?

Answer 21

Glycolysis

Question 22

What is trehalose?

Answer 22

• Non reducing dissacharide joint by 2 glucoses
• Stores carbohydrates
• Protects yeast cells against various stress conditions

Question 23

What does it mean if yeast is viable?

Answer 23

The yeast is alive

Question 24

What does yeast vitality measure?

Answer 24

It measures the health of the yeast

Question 25

What is the typical pitching rate of yeast?

Answer 25

1 million viable cells / mL of wort / °P

Question 26

What is the methylene blue test for yeast?

Answer 26

The yeast cells are treated with methylene blue dye to determine the viability of the yeast cells. Colorless cell = alive cell Blue cell = dead cell

Question 27

What does Aber Biomass Technology do? How does it work?

Answer 27

It is an inline yeast analyzer to count yeast cells. It measures the capacitance of the slurry, More capacitance = more cells

Question 28

What material are most fermentors made of today? Why?

Answer 28

Stainless steel * Very durable * Excellent cleaning properties * Very corrosion resistant * High thermal conductivity

Question 29

Which type of chemical cleaners causes pitting in stainless steel vessels?

Answer 29

Chlorinated caustics

Question 30

What is the name of the traditional open top fermentor?

Answer 30

Yorkshire Square

Question 31

What is the name of this traditional fermentor?

Answer 31

Burton Union

Question 32

What is the benefit of a horizontal cylindrical fermentor?

Answer 32

Large vessels have low hydrostatic pressure

Question 33

What is the most common vessel used for fermentation today?

Answer 33

Cylindroconical

Question 34

What is the most common arrangement of cooling jackets on a cylindroconical fermentor? Why?

Answer 34

5 is most common because it can be used for both fermentation and cold conditioning. 1 and 2 would be used for primary fermentations 3 and 4 would be used for cold conditioning

Question 35

Why is it important to have a cooling jacket on the cone of the fermentor?

Answer 35

Yeast and trub collect and the cooling jacket avoids developing hot spots in the settled material

Question 36

What is the most common angle for cylindroconical vessel cones? Why?

Answer 36

70° * Better mixing * Better yeast collection

Question 37

What is the definition of "cleaning"?

Answer 37

Removing soil and/or biofilm

Question 38

What is the definition of "sanitizing"?

Answer 38

Log 3 reduction (99.9%) of microorganisms in the system

Question 39

What is the definition of "disinfecting"?

Answer 39

Log 5 reduction (99.999%) of microorganisms in the system

Question 40

What is the definition of "sterilizing"?

Answer 40

Complete elimination of all life

Question 41

What are biofilms?

Answer 41

* Microbial communities * From slime or hydrogels

Question 42

Which type of yeast is bottom cropped from a cylindroconical fermentor?

Answer 42

Both ale and lager yeasts are bottom cropped after fermentation is completed

Question 43

What are 3 important vitamins for yeast health?

Answer 43

1. Biotin 2. Thiamine 3. Riboflavin

Question 44

Why is Zinc essential for yeast health?

Answer 44

* Promotes growth and budding of yeast * Binds to amino acids * Increases fermentation rate

Question 45

Why can wort/beer not be stored in copper vessels?

Answer 45

The copper is toxic to yeast at high concentrations. It disrupts the plasma membrane of the cell.

Question 46

Why does yeast require oxygen?

Answer 46

The oxygen is required for the synthesis of sterols and unsaturated fatty acids in the cell membrane

Question 47

What compounds are produced during the Krebs Cycle in a yeast cell?

Answer 47

Organic acids - contribute sour or salty taste to beer

Question 48

What causes the formation of short chain fatty acids (C₆-C₁₀) by yeast?

Answer 48

It is caused by ethanol stress or autolysis of yeast. Results in unpleasant flavors in beer and inhibits beer foam formation

Question 49

What 5 factors promote the production of higher (fusel) alcohols during fermentation?

Answer 49

1. Higher temperatures 2. Temperature changes 3. High or Low levels of FAN or oxygen 4. Agitation during fermentation 5. Low yeast pitching rate

Question 50

How does proper initial aeration of yeast prevent ester formation?

Answer 50

Proper initial aeration leads to good sterol production which will deplete acetyl-CoA and not allow esters to be formed

Question 51

What is POF and which yeast is this commonly (and intentionally) found in?

Answer 51

Phenolic Off Flavors * Belgian strains * German hefeweizen strains * Brettanomyces species