Yeast Fermentation Lab

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Mark Duanmu, Rika Fujita, Alex Chung
October 8, 2011
Biology (Honors) P7

Temperature and Yeast Fermentation

Saccharomyces cerevisiae, commonly known as baker’s yeast, is an key ingredient used mainly when baking bread or making alcoholic beverages. The main role of the yeast is to convert the sucrose into carbon dioxide (CO2) and ethanol. For example, when baking bread, the yeast ferments the sucrose within the dough and so CO2 and ethanol is released, causing the bread to rise and expand. It does this using enzymesAlso, during this fermentation process, because CO2 is released, it starts to form foam and that is why, for example, beer, ends up with a layer of foam above the liquid.

Yeast undergoes an alcoholic fermentation, where it first ferments the reactants, glucose. Glucose, C6H12O6, is then transformed into ethanol (2 C2H5OH) and carbon dioxide (2 CO2).

The purpose of this lab is to find out what effect changes in environmental temperature has on yeast fermentation. To accomplish this, we would need to simulate yeast fertilization, have different temperatures to test it on, and a way to calculate and measure the amount of fertilization. To simulate fertilization, we put 4 tespoons of sucrose with 3 teaspoons of yeast in a glass jar, then added 50 mL of water, to start the reaction. We knew that in order to test the effect of temperature, you would need to change the temperature in the reaction, but also in the environment. So, we put each of the jars in 200mL water filled beakers, which had the same temperature as inside the jar. We also knew that fertilization releases carbon dioxide, so to measure the yeast fermentation, we used a CO2 probe, which was a baton-shaped device that we put in the jar, and it would measure the amount of CO2 in the jar. The CO2 probe connected to a computer, and using logger pro, we would see the change of CO2 during the reaction for 100 seconds, through a graph and a table. The greater the change in CO2, the more fermentation is going on. We did 2 trials of 4 different temperatures: the control (room temperature), ice water, 40C water, and 70C water.

We know that enzymes are usually sped up by heat, since heat creates energy and randomness, but it also has an “optimal temperature”, so that when it gets too hot, enzyme productivity will decline. So, our hypothesis was that since fermentation is a chemical reaction carried out by enzymes, warmer temperatures would speed up the reaction, up to 40C, but at 70C, it would be a bit lower- because the temperature is not optimum.

Control Treatment and Variables:
Independent Variable: The temperature of the water
Dependent Variable: The amount of fermentation
Standardized Variable: The amount of yeast, amount of sucrose, amount of water, and the amount of time

250 mL of ice water, room temperature water, 40٥C water, and 70٥C water (50 mL to mix with the sucrose and yeast, 200 mL for the beaker) 32 teaspoons of sucrose (4 teaspoons per trial)
24 teaspoons of yeast (3 teaspoons per trial)
CO2 probe
1 test bottle
4 beakers
1 graduated cylinder
1 funnel


|Ice water |40٥C water |70٥C water | |[pic] |[pic] |[pic] |

1. Label the 4 beakers ice water, room temperature water, 40٥C water, and 70٥C water 2. Fill each beakers with 200 mL of water according to the labels 3. Using the funnel, put 3 teaspoons of yeast and 4 teaspoons of sucrose into the test bottle 4. Then add 50 mL of room temperature water and shake the bottle so that the yeast, sucrose and water is well mixed 5. Place the test bottle into the beaker labeled under room temperature water and insert the CO2 probe into the bottle. Make...
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