Unit 2 - Lesson 8 - Yeast Flashcards
What are yeast cells?
Single-celled micro-organisms and member of the fungus kingdom
Can be cultivated or found in nature
Very small and seen at 100x magnification
What is the yeast genus & species used in fermentation?
Genus: Saccharomyces - derives from Greek word sugar and mushroom “sugar fungus”
Species: S. Cerevisiae - wine, baking, distilled & brewing
Cerevisiae = Latin for beer
What are yeast cells structures?
Nucleus Mitochondrion Vacuole Inner Plasma Memb Rane Daughter Cells Cell Wall
How small are yeast cells?
5-10 microns and ellipsoid in shape
What is the Yeast Cell Structure?
2 outer layers (cell wall and inner membrane)
Inner with nucleus, vacuole, mitochondria and nutrients
What is the yeast’s cell wall made of?
Protein and polysaccharides
What does the plasma membrane in the yeast cell accomplish?
Allows molecules in and out of the cell
Regulates unfermented materials taken in the cell
How thick is a yeast cells wall?
100-200 nano microns
Wall thickens when cell reached post fermentation stage
What are bud scars?
Scares withiin a yeast cell indicating age.
Older yeast produces more buds and hence more scars
What are 2 indicators of age in yeast?
Bud scars
Shape, size and # of vacuoles which change with age
What environment can yeast operate?
Both aerobic and anaerobic
How does yeast function under aerobic conditions?
With little other microbiological activity, ample carbs and nutrients yeast will multiply
Used for commercial production
How does yeast function under anaerobic environment?
Exothermic - energy release
Assuming no other microbial activity, suitable carbs and nutrients - yeast converts carbs into alcohol, CO2 and flavor compounds
How do yeast cells multiply?
Asexually - through budding from a mother cell
Each bud leaves a scar on mother and smaller one on daughter cells
How do you determine yeast cells age?
Count the bud scars
What is the fluid called within the yeast cell?
Cytoplasm
What is a threat at the beginning of fermentation to yeast?
Other microbial contamination
When creating commercial yeast in an aerobic environment how is that done?
- Harvested at various solids concentration through rotary vacuum or dewatering
- Three yeast products are formed (Cream, Pressed (cake) and Dried)
What are the 3 yeast products from commercially grown yeast and their respective water content?
Cream yeast - 18% dry
Pressed Yeast - 25% dry
Dried Yeast - 95% dry
What determines yeast product (cream, pressed or dried)?
- Scale of spirits production
- Distillery location
- Auto vs manual control
- On-site storage capability
- Availability of required strain
What is cream yeast suitable for?
Large-scale production - Delivered in tankers Requires 1. On-site cream storage 2. Automated delivery 3. Rapid turnover
When is Dried Yeast suitable?
Best for smaller scale
- Limited delivery options
- Manual reactivation into liquid stream
- Manual addition
- Climatic conditions less important vs cream yeast
When is pressed yeast suitable?
Small to medium production
Sites require refrigeration storage
What are some other forms used in yeast fermentation aside from commercial yeast?
Cereal bassed unfermented liquor
Molasses based liquor
Small-scale yeast propagation
Brewers yeast - not common anymore
