Lesson 3 - Yeast Morphology and Evaluation SAQ
This lesson allows you to test yourself on the material covered in the Yeast Morphology and Evaluation lesson, and determine the level to which you have met the learning outcomes.
Suggested Response - Q3
** The budding process, in which brewing yeast cells multiply, is an asymmetric process. What does this mean, and what are its consequences?
Response:
Yeast budding is an asymmetric process. Although the two resultant cells are usually genetically identical, they are not exact copies of each other. The cell that has formed a new bud is called the mother. The new cell is called the daughter. Mothers are always larger than daughters. New daughter cells cannot begin to bud themselves until they have reached a critical size. Each yeast cell can only bud a finite number of times; this property is strain-specific. Once this limit is reached, the cell will die (assuming it has not been prematurely killed as a result of another lethal stress). In other words, all cells have a finite lifespan during which they will age and eventually die.
This means that populations of brewing yeast cells always consist of cells of varying age. Both very old cells and new daughter cells do not have the same metabolic capabilities as middle-aged and mature cells. From a practical point of view, older cells are physically larger than younger cells. At some stage in the fermentation process, excess yeast is separated from the beer. As a proportion is retained for reuse, the cropping procedure might select a fraction that is enriched in older, less able cells. If this happens, the quality of the yeast and its efficacy is likely to deteriorate with each successive fermentation cycle.