Yeast Fermentation and Temperature

Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required

Categories: Reaction Rate, Enzymes and Digestion, Microbiology

Alternative titles:

Summary

Yeast cells ferment sugar to produce carbon dioxide and alcohol. This experiment investigates how temperature affects the rate of fermentation by measuring the amount of foam or gas produced by yeast in sugar solution at different temperatures.

Procedure

Prepare four boiling tubes or similar containers and label them for different temperature conditions.
Add equal amounts of yeast to each tube.
Prepare a warm sugar solution and use a pipette to add the same amount to each tube.
Place each tube in water baths or environments set at different temperatures.
Allow the yeast mixtures to react for a set amount of time (for example, 5-minute intervals over 20 minutes).
Observe and record the amount of foam or gas produced in each tube at each time interval.
Compare results to determine which temperature produced the greatest amount of carbon dioxide.

Links

Yeast fermentation Experiment 1- Temperature - Ysgol Eirias Technology Department:

Temperature and Fermentation in Bread Yeast - Samuel Holloway:

Variations

Use different types of sugar (glucose, sucrose, fructose) to compare fermentation rates.
Test the effect of pH on yeast fermentation instead of temperature.
Use balloons fitted over the tops of the tubes to measure gas volume more precisely.

Safety Precautions

Use caution with hot water baths to avoid burns.
Dispose of yeast mixtures down the sink with plenty of water after the experiment.
Ensure students aren't tempted to taste the resulting mixture with alcohol.

Questions to Consider

What is the relationship between temperature and yeast fermentation rate? (The rate increases with temperature up to an optimal point, then decreases as enzymes denature.)
Why does the amount of foam or gas indicate the rate of fermentation? (Carbon dioxide is a product of yeast respiration, so more gas means faster fermentation.)
What happens to yeast enzymes at very high temperatures? (They become denatured and stop functioning.)
How could you make this experiment more accurate? (Use precise thermometers, control all variables, and repeat trials.)