Lecture 3 Flashcards
What is the cumulative effect of yeast growth on wort?
Fermentation,
ultimately resulting in the spent growth medium, beer
What is the art of fermentation?
Manage yeast growth and metabolism
Produce desired spent growth medium.
What are the major stages fermentation ?
Lag phase, Log phase, Deceleration phase, Stationary phase.
What happens during the lag phase of fermentation?
Yeast adapts from stationary to growth phase, intense metabolic activity, most oxygen consumed to make sterols, critical influence on fermentation outcome.
What characterizes the log phase of fermentation?
-Most active phase
-maximum growth rate,
yeast double in number at a defined rate
-high sugar assimilation
-accumulation of biomass, ethanol, CO2
-formation of flavor active metabolites
-max exothermy
-rapid pH decline.
What occurs during the deceleration phase of fermentation?
End of primary fermentation, onset of yeast flocculation, maximum yeast separation from green beer, minimum pH achieved.
What is notable about the stationary phase of fermentation?
Yeast proliferation ceases, fermentable sugars depleted, yeast experiences maximum stress, moderate pH rise, some flavour changes occur.
What is the relationship between dried biomass and gravity in fermentation?
Dried biomass increases as gravity decreases.
What are the key performance indicators (KPIs) for fermentation?
Total cycle time, final gravity, VDK specification, ethanol yield, yeast crop size and viability, beer flavour, total beer yield.
What does wort contain?
Contains fermentable sugar, nitrogen, salts, metal ions, vitamins, affects C:N ratio, critical for balanced nutrient supply.
What is the effect of key process variables on fermentation?
Effects on fermentation cycle time, fermentation efficiency, development of flavours
How is fermentation typically controlled in large-scale operations?
Passive control systems with established values for key variables, cooling to maintain temperature, monitoring via off-line sample analysis.
What are some uncontrolled variables in large-scale fermentations?
Pitching yeast physiology (due to storage), wort composition, pitching rate, wort oxygenation, fermenter design and operation.
effect of too high oxygen
rapid fermentation rate, high yeast growth, reduced ethanol yield.
effect of too little oxygen in fermentation
low yeast growth, slow fermentation that may get stuck, low crop viability
