Yeast/Fermentation Flashcards
What is the ale yeast called?
Saccharomyces cerevisiae
What is the lager yeast called?
Saccharomyces pastorianus
What is the differene between anaerobic and anoxic?
Anaerobic = metabolic process without oxygen
Anoxic = environment without oxygen
What two yeast species combined to form S. pastorianus?
S. cerevisiae and S. eubayanus
What are the 3 distinct traits of lager yeast?
- Bottom fermenting
- Utilizes melibiose
- Cannot grow at 37°C
What are the 3 distinct traits of ale yeast?
- Top fermenting
- Cannot utilize melibiose
- Can grow at 37°C
What family of fungi does brewing yeast belong to?
Ascomycota
What are the designations for the 2 haploids that sexually reproduce to form the yeast dipolid?
“a” haploid and “alpha” haploid
Where is the DNA stored in the yeast cell?
The nucleus
How many chromosones does brewing yeast contain?
16
What are yeast cell membranes composed of?
Phospholipids
They have a polar head and nonpolar head to form the cell membrane
What are the 5 methods of tranport through the yeast cell membrane?
- Facilitated diffusion
- Active transport
- Symport
- Antiport
- Passive diffusion
What effect does ethanol have on yeast cell membranes?
- Denatures proteins
- Displaces water of hydration
- Disrupts membranes by acidifying cytoplasm
What is the Lectin-based Flocculation Hypothesis?
- Zymolectin proteins in the outer cell walls bind to mannose sugars in the cell walls of nearby yeast
- Ca is essential for binding
What is the maximum number of bud scars that a yeast cell can have?
~40 scars
What is the significance of the p- mutant?
It is a petite mutant that contains mutations in the mtDNA genome
What is the significance of the p0 mutant?
It is a petite mutant that has lost mtDNA genome
What is the purpose of the vacuole in the yeast cell?
- Provides dynamic storage
- Breaks down proteins
What order will yeast use the following sugars?
Maltose, maltotriose, glucose, dextrin
- Glucose
- Maltose
- Maltotriose
Dextrin is never used by the yeast cell
What is the process called that transforms amino acids into keto acids?
Trans-amination
What is the process called that transforms glucose into pyruvate?
Glycolysis
What is trehalose?
- Non reducing dissacharide joint by 2 glucoses
- Stores carbohydrates
- Protects yeast cells against various stress conditions
What does it mean if yeast is viable?
The yeast is alive
What does yeast vitality measure?
It measures the health of the yeast
What is the typical pitching rate of yeast?
1 million viable cells / mL of wort / °P
What is the methylene blue test for yeast?
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
What does Aber Biomass Technology do? How does it work?
It is an inline yeast analyzer to count yeast cells.
It measures the capacitance of the slurry,
More capacitance = more cells
What material are most fermentors made of today? Why?
Stainless steel
- Very durable
- Excellent cleaning properties
- Very corrosion resistant
- High thermal conductivity
Which type of chemical cleaners causes pitting in stainless steel vessels?
Chlorinated caustics
What is the name of the traditional open top fermentor?
Yorkshire Square
What is the name of this traditional fermentor?
Burton Union
What is the benefit of a horizontal cylindrical fermentor?
Large vessels have low hydrostatic pressure
What is the most common vessel used for fermentation today?
Cylindroconical
What is the most common arrangement of cooling jackets on a cylindroconical fermentor? Why?
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
Why is it important to have a cooling jacket on the cone of the fermentor?
Yeast and trub collect and the cooling jacket avoids developing hot spots in the settled material
What is the most common angle for cylindroconical vessel cones? Why?
70°
- Better mixing
- Better yeast collection
What is the definition of “cleaning”?
Removing soil and/or biofilm
What is the definition of “sanitizing”?
Log 3 reduction (99.9%) of microorganisms in the system
What is the definition of “disinfecting”?
Log 5 reduction (99.999%) of microorganisms in the system
What is the definition of “sterilizing”?
Complete elimination of all life
What are biofilms?
- Microbial communities
- From slime or hydrogels
Which type of yeast is bottom cropped from a cylindroconical fermentor?
Both ale and lager yeasts are bottom cropped after fermentation is completed
What are 3 important vitamins for yeast health?
- Biotin
- Thiamine
- Riboflavin
Why is Zinc essential for yeast health?
- Promotes growth and budding of yeast
- Binds to amino acids
- Increases fermentation rate
Why can wort/beer not be stored in copper vessels?
The copper is toxic to yeast at high concentrations. It disrupts the plasma membrane of the cell.
Why does yeast require oxygen?
The oxygen is required for the synthesis of sterols and unsaturated fatty acids in the cell membrane
What compounds are produced during the Krebs Cycle in a yeast cell?
Organic acids - contribute sour or salty taste to beer
What causes the formation of short chain fatty acids (C6-C10) by yeast?
It is caused by ethanol stress or autolysis of yeast. Results in unpleasant flavors in beer and inhibits beer foam formation
What 5 factors promote the production of higher (fusel) alcohols during fermentation?
- Higher temperatures
- Temperature changes
- High or Low levels of FAN or oxygen
- Agitation during fermentation
- Low yeast pitching rate
How does proper initial aeration of yeast prevent ester formation?
Proper initial aeration leads to good sterol production which will deplete acetyl-CoA and not allow esters to be formed
What is POF and which yeast is this commonly (and intentionally) found in?
Phenolic Off Flavors
- Belgian strains
- German hefeweizen strains
- Brettanomyces species
