Yeast Metabolism Flashcards
(19 cards)
What is the simplified equation of fermentation?
GRAPE SUGAR + YEAST = ETHYL ALCOHOL + CARBON DIOXIDE + HEAT
This is represented as C6H12O6 + Yeast = 2CH3CH2OH + 2CO2
What is the role of yeast cells in fermentation?
Yeast cells function as ‘enzymatic factories’ that catalyse chemical transformations through specific enzymes.
Name three key enzymes involved in yeast metabolism.
- Hexokinase
- Phosphofructokinase
- Glyceraldehyde 3 phosphate dehydrogenase
What is glycolysis in the context of yeast metabolism?
A metabolic pathway where one sugar molecule is converted into two pyruvate molecules, water, and two ATP.
What happens to pyruvate under anaerobic conditions in yeast fermentation?
The bulk of pyruvate is converted to alcohol.
What is the fermentation pathway for pyruvate?
Pyruvate → Ethanal (acetaldehyde) + CO2 → Ethanol
The first step is catalysed by pyruvate decarboxylase, and the second is a reduction by alcohol dehydrogenase.
What characterizes glyceropyruvic fermentation?
Transforms sugar into glycerol and pyruvate, is energy-neutral, and produces less ethanol.
True or False: The Pasteur effect describes the stimulation of ethanol fermentation by oxygen.
False
What does the Crabtree effect describe?
The production of ethanol by certain yeasts in the presence of oxygen due to high glucose concentrations.
What is required for yeast to synthesize amino acids?
A carbon skeleton (often from pyruvate) and a source of nitrogen (usually ammonium ions).
What are the by-products of amino acid catabolism in yeast?
- Higher alcohols
- Hydrogen sulphide
How are esters formed during fermentation?
From the reaction of alcohols and carboxylic acids.
What factors can lead to acetic acid production during fermentation?
- Low pH
- High pH
- High sugar must
- Nutritional deficiencies
- Over clarification
- High temperature
What is the significance of understanding yeast metabolism in wine production?
It is crucial for controlling fermentation and influencing the final characteristics of the wine.
What factors significantly impact yeast behaviour and by-product formation?
- Oxygen availability
- Sugar concentration
- Nutrient levels
- pH
- Temperature
What should winemakers manage to promote desirable flavour compounds?
Factors like oxygen availability, sugar concentration, nutrient levels, pH, and temperature.
Fill in the blank: The bulk of pyruvate in yeast fermentation is converted to _______.
alcohol
What can higher alcohols produced during fermentation affect?
They can be detrimental to flavour when present in high levels.
What is the impact of hydrogen sulphide (H2S) in fermentation?
It is organoleptically important and can form from the catabolism of sulphur-containing amino acids.
