4 Flashcards
What marks the start of fermentation?
Pitching.
What should pitching rate control systems achieve?
- Precise control of initial yeast count
- Repeatable control of initial yeast count
- Yeast evenly dispersed throughout wort
- Instantaneous contact between yeast and wort
- Addition of minimum amount of non-yeast solids and dead cells.
What is more important in real-world pitching systems, repeatability or absolute accuracy?
Repeatability.
How is pitching rate expressed?
- Directly as cell count (total and/or viable) per unit volume of wort
- Indirectly as weight or volume of yeast added.
What is the first step in the yeast pitching process?
Select the yeast to be pitched
What criteria should be considered for yeast selection?
- Right strain
- Viability
- Microbiological status
- Generation number
- Previous fermentation performance
- Time in yeast storage vessel
- Availability.
What is a pressed yeast cake?
Yeast recovered from previous fermentation, filtered, and stored in a cold room.
What are the advantages of using direct weight of yeast cake?
- Simple
- Inexpensive
- No requirement for trained/skilled personnel.
What are the disadvantages of using direct weight of yeast cake?
- No correction for viability
- No correction for non-yeast solids
- No opportunity to examine yeast cells
- Heterogeneous sample.
What is the most common form of pitching yeast storage?
Yeast slurry in beer.
What is required for hygienic sampling from a yeast storage vessel?
A hygienic sample tap.
What does the determination of spun solids involve?
Centrifuging a known weight of yeast slurry and calculating the percentage of spun solids.
What is the method used to determine the viability of yeast cells?
Prepare a suitable dilution of yeast slurry and stain with methylene blue
dead cells stain blue
What technology is used for rapid automated yeast cell counting?
Aber Countstar.
What are the advantages of viable spun solids determination?
- Simple
- Uses readily available lab equipment
- Provides opportunity for microscopic examination of yeast.
What are the disadvantages of total and viable cell count analysis?
- Requires trained/skilled personnel for determination of viability
- Small sample size.
What is a Coulter counter used for?
An electronic counter based on change in impedance as particles pass through a detector.
What are the disadvantages of using particle counters?
- Relatively expensive
- No correction for non-yeast solids
- Requires separate viability determination.
