Measuring the Rate of Alcohol Fermentation in Yeast Cells

Measuring the Rate of Alcohol Fermentation in Yeast Cells

The objective of this experiment was to determine the relative rate of alcohol fermentation in yeast reacting with malt and corn syrup with different amounts of yeast in each trial. Alcoholic Fermentation is a metabolic pathway where glucose is broken down into carbon dioxide and ethanol. Aerobic respiration requires oxygen in order to generate energy (ATP). Although carbohydrates, fats, and proteins can all be processed and consumed as reactant, it is the preferred method of pyruvate breakdown in glycolysis and requires that pyruvate enter the mitochondrion in order to be fully oxidized by the Krebs cycle. Through this process some glucose is converted to ATP. This pathway is a chain of enzyme-catalyzed reactions. (Pearson 2009) Many times, however the term alcohol fermentation is constrained to the actions preformed by enzymes which are known as ferments. Ferments are produced by bacteria, mold and yeast (Discovery 2009). Yeast is a single celled fungus that can break down glucose through fermentation. Yeast is used in many products because of its production of carbon dioxide. This causes bread to rise. Yeast can be used to make ethyl alcohol in the beer and wine industry (Barron’s 2007). Although glucose is at the start of the pathway, other molecules can be transformed to glucose, such as sucrose, fructose, and the other substances used in this experiment: malt and corn syrup (Pearson 2009). It was found the lab that was preformed earlier, that all enzymes have optimal pH, salinities, and temperatures (Pearson 2009). According to Pampulha and Lourier-Diaz (1989), the most favorable pH for the yeast cells is between 7.0 and 7.2. In this experiment, Pampulha and Lourier-Diaz found that when acetic acid was added to solutions of fermenting yeast, that the fermentation rate dropped and there was a drop in the internal pH of the yeast cells. According to Michael Benedik (2001), the yeast’s optimal temperature is between 30 and 35 degrees Celsius. The hypothesis was created from the information that the more yeast present, the faster the rate and the greater the overall amount of fermentation will be.

Materials and Methods:
In this experiment, the amount of carbon dioxide was measured to record the relative rate of fermentation in test tubes containing varying amounts of yeast, water and corn syrup or malt. The first test tube had 4mL of water, no yeast suspension and 3mL of malt or corn syrup. The second contained 3mL of water, 1mL of yeast, and 3mL of malt or corn syrup. The final tube held 1mL of water, 3mL of yeast, and 3mL of yeast or corn syrup. There were six test tubes in all; there were three to test the rate of fermentation when yeast broke down corn syrup and three others to do the same but with yeast and malt. These tubes were placed upright in a test tube rack put in warm water and attached to plastic tubing to tubes filled with water placed upside down in the test tube rack. A cork held the tubing inside the fermenting tube to make sure that the carbon dioxide produced traveled directly to the water tube. Once all tubes were set up, the distance in mm from the baseline water level was measured every five minutes.

Fermentation Tube (volume in ml)
1 2 3 4 5 6
Water 4 3 2 4 3 1
Yeast 0 1 3 0 1 3
Corn Syrup 3 3 3 - - -

Sucrose - - - 3 3 3

Tube Minutes Abs
0 5 10 15 20 25 30
1 - - - - - - - 0.676
2 0.6 0.7 0.8 0.8 0.8 0.8 0.627
3 0.5 0.6 0.7 0.8 0.8 0.8 0.32
4 - - - - - - 0.016
5 0.6 0.6 0.6 0.6 0.6 0.6 0.66
6 0.6 0.8 0.8 0.8 0.9 0.9 0.69

Table 1 shows the results of yeast and malt fermentation in terms of change in water level in the upside down water tube and demonstrates that test tube three had the biggest amount of fermentation taking place. As shown above test tube one, which had no yeast and 3mL of malt, showed no change in water level. It is concluded that no fermentation took place. Test tube two held 3mL of malt and 1mL of yeast and also showed no change in water level. This contradicted the hypothesis since both yeast and malt were present. Test tube three contained the most yeast (3mL) and had the most significant amount of change in the water line at the end of the period. Table 2 lists the results of the corn syrup and yeast fermentation and explains that test tube three had the greatest amount of fermentation. Test tube one contained no yeast and did not have any change in the amount of water. Test tube two contained 3mL of corn syrup and 1mL of yeast and had steady changes in the water line over time, the biggest change happened between 25 and 30 minutes. Test tube three had 3mL of corn syrup and 3mL of yeast. Overall, this particular tube had the most amount of fermentation that occurred.

If there is a large amount of substrate and enzyme is added to the mixture, the reaction rate ¬¬-increases (Kenyon 73). The results from the experiment are consistent with this idea and prove that in the test tubes that did have more yeast, more fermentation occurred. However test tube three in the malt fermentation did not exhibit the expected results. This may happened because of the rubber tubing connecting the fermenting tube to the water tube may have had a tear or because the yeast settled in the tube and did not interact with the malt. It is also possible that the right amounts of malt and yeast were not really added to the tube. It was difficult to precisely measure the amount of water displacement because water kept dripping out, this could have led to errors. Despite the possible mistakes that were made the general idea collected from the experiment was that in the tubes that had more yeast had more water displaced over the measuring period. Therefore, these results support the idea that the more yeast that is present, the more fermentation will occur. There are other ways to measure the amount of carbon dioxide produced by yeast fermentation. A more precise way would be to use a carbon dioxide detector and do each “run” with the test tube separately. A less accurate, more unreasonable way would be to attach a deflated balloon to the top each test tube and secure it with rubber bands and tape.

Work Sited

Benedik, Michael. "How Does Temperature Affect Yeast Activity?" Mad Sci Network.
Michael Benedik, 30 Jan. 2001. Web. 5 Nov. 2009. .

Fermentation. Funk & Wagnalls. 2005. Discovery Education. 8 November 2009

Goldberg, Deborah T. AP biology. Hauppauge, N.Y: Barron's Educational Series, 2007.

Kenyon, Lisa O. Symbiosis. New York: Pearson, 2009. Print.

Pampulha, M. E., and M. C. Loureiro-Dias. "Combined effect of acetic acid, pH and
ethanol on intracellular pH of fermenting yeast." Applied Microbiology and Biotechnology 31 (1989): 547-50. SpringerLink. 29 Nov. 2004. Web. 5 Nov. 2009.