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MBCP 2021 > Yeast/Fermentation > Flashcards

Yeast/Fermentation Flashcards

1
Q

What is the ale yeast called?

A

Saccharomyces cerevisiae

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2
Q

What is the lager yeast called?

A

Saccharomyces pastorianus

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3
Q

What is the differene between anaerobic and anoxic?

A

Anaerobic = metabolic process without oxygen

Anoxic = environment without oxygen

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4
Q

What two yeast species combined to form S. pastorianus?

A

S. cerevisiae and S. eubayanus

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5
Q

What are the 3 distinct traits of lager yeast?

A
  1. Bottom fermenting
  2. Utilizes melibiose
  3. Cannot grow at 37°C
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6
Q

What are the 3 distinct traits of ale yeast?

A
  1. Top fermenting
  2. Cannot utilize melibiose
  3. Can grow at 37°C
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7
Q

What family of fungi does brewing yeast belong to?

A

Ascomycota

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8
Q

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

A

“a” haploid and “alpha” haploid

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9
Q

Where is the DNA stored in the yeast cell?

A

The nucleus

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10
Q

How many chromosones does brewing yeast contain?

A

16

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11
Q

What are yeast cell membranes composed of?

A

Phospholipids

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

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12
Q

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

A
  1. Facilitated diffusion
  2. Active transport
  3. Symport
  4. Antiport
  5. Passive diffusion
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13
Q

What effect does ethanol have on yeast cell membranes?

A
  • Denatures proteins
  • Displaces water of hydration
  • Disrupts membranes by acidifying cytoplasm
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14
Q

What is the Lectin-based Flocculation Hypothesis?

A
  • Zymolectin proteins in the outer cell walls bind to mannose sugars in the cell walls of nearby yeast
  • Ca is essential for binding
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15
Q

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

A

~40 scars

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16
Q

What is the significance of the p- mutant?

A

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

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17
Q

What is the significance of the p0 mutant?

A

It is a petite mutant that has lost mtDNA genome

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18
Q

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

A
  • Provides dynamic storage
  • Breaks down proteins
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19
Q

What order will yeast use the following sugars?

Maltose, maltotriose, glucose, dextrin

A
  1. Glucose
  2. Maltose
  3. Maltotriose

Dextrin is never used by the yeast cell

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20
Q

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

A

Trans-amination

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21
Q

What is the process called that transforms glucose into pyruvate?

A

Glycolysis

22
Q

What is trehalose?

A
  • Non reducing dissacharide joint by 2 glucoses
  • Stores carbohydrates
  • Protects yeast cells against various stress conditions
23
Q

What does it mean if yeast is viable?

A

The yeast is alive

24
Q

What does yeast vitality measure?

A

It measures the health of the yeast

25
Q

What is the typical pitching rate of yeast?

A

1 million viable cells / mL of wort / °P

26
Q

What is the methylene blue test for yeast?

A

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

27
Q

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

A

It is an inline yeast analyzer to count yeast cells.

It measures the capacitance of the slurry,

More capacitance = more cells

28
Q

What material are most fermentors made of today? Why?

A

Stainless steel

  • Very durable
  • Excellent cleaning properties
  • Very corrosion resistant
  • High thermal conductivity
29
Q

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

A

Chlorinated caustics

30
Q

What is the name of the traditional open top fermentor?

A

Yorkshire Square

31
Q

What is the name of this traditional fermentor?

A

Burton Union

32
Q

What is the benefit of a horizontal cylindrical fermentor?

A

Large vessels have low hydrostatic pressure

33
Q

What is the most common vessel used for fermentation today?

A

Cylindroconical

34
Q

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

A

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

35
Q

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

A

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

36
Q

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

A

70°

  • Better mixing
  • Better yeast collection
37
Q

What is the definition of “cleaning”?

A

Removing soil and/or biofilm

38
Q

What is the definition of “sanitizing”?

A

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

39
Q

What is the definition of “disinfecting”?

A

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

40
Q

What is the definition of “sterilizing”?

A

Complete elimination of all life

41
Q

What are biofilms?

A
  • Microbial communities
  • From slime or hydrogels
42
Q

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

A

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

43
Q

What are 3 important vitamins for yeast health?

A
  1. Biotin
  2. Thiamine
  3. Riboflavin
44
Q

Why is Zinc essential for yeast health?

A
  • Promotes growth and budding of yeast
  • Binds to amino acids
  • Increases fermentation rate
45
Q

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

A

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

46
Q

Why does yeast require oxygen?

A

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

47
Q

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

A

Organic acids - contribute sour or salty taste to beer

48
Q

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

A

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

49
Q

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

A
  1. Higher temperatures
  2. Temperature changes
  3. High or Low levels of FAN or oxygen
  4. Agitation during fermentation
  5. Low yeast pitching rate
50
Q

How does proper initial aeration of yeast prevent ester formation?

A

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

51
Q

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

A

Phenolic Off Flavors

  • Belgian strains
  • German hefeweizen strains
  • Brettanomyces species

MBCP 2021 (18 decks)

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