Lab Report: Effect of Temperature on Yeast Fermentation Rate

Abstract

We have tested the affects of increased temperature above room temperature on the rate of fermentation of yeast. We had 6 flasks filled with 6mL DI water, 2mL Yeast suspension and 6mL glucose of which 3 were at 25°C and 3 were at 37°C. The flasks at 37°C had each mixture pre-heated at 37°C for 2 minutes before being combined and then added to the flask where it was put into the bath heated to 37°C. We then checked CO2 levels in each flask every 2 minutes for 20 minutes.

We came out results that showed a marginal difference between the amounts of CO2 produced at different temperatures. The results showed that increased temperature causes an increase in fermentation rate and increased production of CO2.

Introduction

Fermentation is the break down of organic matter, by microorganism, in the absence of oxygen also known as anaerobic (Van Neil, 2008). Our reactions occurs when yeasts is added to a solution of glucose and water. Fermentation starts with a process called glycolysis.

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In glycolysis Glucose is broken down into two molecules of pyruvate and a net yield of 2 NADH (electron carrier) and 2 ATP (adenosine triphosphate) molecules. The first step of glycolysis is the energy investment phase. In which 2 ATP’s are added to the Glucose molecule, which produces 2 ADP’s and Fructose 1, 6-biphosphate. This is followed by the energy payoff phase. In this phase NAD+ is reduced to NADH and ADP is reduced to ATP. The total number of ATP created is 4 and 2 NAHDH. After the energy payoff phase what is left is 2 pyruvates.

Fermentation then takes place only in the absence of oxygen. In fermentation the pyruvate is converted into ethyl alcohol, through the oxidation of the 2 NADH molecules, which returns them to two NAD+’s (Freeman, 2011). Oxidation is the loss of an electron in this case H+. We used information from previous labs in which we tested yeasts ability to break down disaccharides, sugar in that case, at different temperatures and found that 37°C was the optimal temperature for yeast to break down sugar, to formulate our hypothesis. Our sources we collected also indicated that different yeasts have different optimal operating temperatures, such as baker’s yeast, which requires higher temperature for yeast to ferment the proteins (Fell, 2008).

Since we were using bakers yeast in our experiment we therefore came to the conclusion that increased temperature would increase yeasts ability to ferment glucose. Using this information and our sources we came up with the hypothesis that increasing the temperature of the solution would increase the rate of fermentation. We thought this was a reasonable hypothesis based upon earlier results from our other lab on temperatures affect on the yeasts ability to break down disaccharides. The predictions we came up with for the results of our tests were that the flasks at 37°C would have a much more accelerated rate of CO2 production then that of the 25°C Flasks.

Materials and Methods

In the experiment we obtained 9 small beakers and 6 fermentation flasks. In the one beaker we added 18mL of Glucose. In the next we added 6ml of Yeast Suspension followed by another beaker with 18ml of distilled water. We then took those 3 beakers and placed them in the incubating bath set at 37˚C for 5 minutes. After 5 minutes took the beakers out and added 6mL of distilled water, 2mL of yeast suspension and 6mL of Glucose into 3 separate beakers and mixed them together.

We then immediately added them at the same time to separate fermentation flasks and measured their CO2 levels using a ruler. We then placed them in the incubating bath set for 37˚C and set out timer for 2 minutes. We then prepared 3 beakers using 6mL of distilled water, 2mL yeast suspension and 6mL Glucose solution. Except that this time the yeast, water and glucose was a room temperature (25˚C). We then proceeded to pour these mixtures into 3 separate fermentation flasks and measured their CO2 levels using a ruler. We then set a timer for 2 minutes. Each time the timer went off we would check the CO2 levels using a ruler. We continued to repeat this checking every 2 minutes for 20 minutes for each set of flasks.

Results

My results indicated that increased temperature increased the rate of fermentation. In the CO2 Evolution graphs it is clear that as time increased as 2-4 minutes you can see a noticeable increase in the level of CO2 in the fermentation flask. As time increases that difference only increases and increases. Then when you look and the average alcohol fermentation graph it is clear that in total amount of CO2 produced in the flasks fermented in the 37˚C incubating bath were much quicker in the process of fermentation, so therefore they produced much more CO2 then those at room temperature (25˚C).

Discussion

My Data supported my hypothesis. Each of my graphs data supported this finding. In the graph showing CO2 evolution the data showing 37˚C had a steep positive slope, while the 25˚C data showed an almost unnoticeable positive slope. This shows how over time the fermentation in the flasks at 37˚C had a noticeable increase in its rate. The other graph shows the overall production of CO2 for each set of flasks. For the flasks at 25˚C their average CO2 produced was .7mm, while the flasks at 37˚C produced on average was 9.2mm. This increase rate and total production increase from that at 25˚C and 37˚C without a doubt supported my hypothesis.

Also our minimization of errors landed itself to accurate results. We minimized any error by having the same person measure levels of CO2 and measure out substances such as yeast suspension. This increases my confidence that the results of our experiment not only support my hypothesis, but also supports that our bodies’ temperature (37˚C) is the optimal temperature for cell respiration and not room temperature. Another follow-up experiment that could be used to give more detailed information about what happened is an experiment in which you run the same test, except include a 3rd condition in which the temperature is below room temperature such as 0˚C. This could show the increase from freezing to room temperature and room temperature to 37˚C.

Conclusion

The results of this experiment support the hypothesis that increasing the temperature of the solution would increase the rate of fermentation. The data showed a clear and significant difference in the rate of CO2 production between the 25°C and 37°C conditions. The 37°C condition exhibited a much faster and more efficient fermentation process, resulting in significantly higher CO2 production.

Future Research

Future research could explore the effects of temperature variations beyond the range tested in this experiment. Additionally, investigating the impact of temperatures below room temperature, such as 0°C, would provide valuable insights into the temperature dependence of yeast fermentation. Exploring different yeast strains with varying optimal operating temperatures could also contribute to a more comprehensive understanding of this biological process.

References:

1. Cornelias B Van Niel, “Fermentation,” in AccessScience, ©McGraw-Hill Companies, 2008. Web.
2. Freeman, Scott. Biological Science. 4th ed. Boston: Benjamin Cummings, 2011. Print.
3. Jack W. Fell, Herman J Phaff, Graeme M. Walker, “Yeast,” in AccessScience, ©McGraw-Hill Companies, 2008. Web.
4. Reddy. "Effect of Fermentation Condition on Yeast Growth and Volatile Composition of Wine Produced from Mango Fruit Juice." Food & Biproducts Processing: Transactions of the Institute of Chemical Engineers Part C 89.4 (2011): 487-91. EBSCO. Web. 2 Oct. 2012. Web.