Lab 8: Fermentation Rates Among Various Yeasts
Biology 1101 Laboratory, Section 013
Instructor: Megan Novak
October 25, 2018
I certify that the work presented here is my own. I have cited sources appropriately, have paraphrased correctly, and have written the work myself. I have not shared my work with other students enrolled in Biology 1101, nor have I acquired this work from other students enrolled in Biology 1101, students previously enrolled in Biology 1101, or papers previously written for any Biology course.
Cellular respiration is a process that is responsible for the breakdown of sugars to be used by cells. Respiration is completed by most organisms on the Earth and is an aerobic process, meaning that oxygen is required to complete the process (Cain et al., 2016. 168). When oxygen is not present, organisms carry out one of the two types of fermentation: alcohol fermentation or lactic acid fermentation. Fermentation occurs without oxygen and produces ATP through the regeneration of NAD+. Alcohol fermentation produces ethanol, or alcohol, as a byproduct, and lactic acid fermentation produces lactate (Cain et al., 2016. 180-181).
The brewing of common alcoholic beverages, such as beer and champagne have the common identity of being a fermentation product of various yeasts. The fermentation and creation of alcoholic beverages is an anaerobic process, with alcohol and CO2 as waste products. In the 19th century, Louis Pasteur determined that yeasts were responsible for the nature of alcohol fermentation. In the fermentation of wines, Pasteur Champagne, a strain of S. bayanus is commonly used. However, the sugars found in the grapes of wine typically fuel the fermentation process and creation of alcohol at temperatures near 20°C (Combina, 2005). In contrast, most beers use strains of yeast in the genus Saccharomyces- S. cervisiae. These are a type of sugar fungus that are commonly incorporated into the brewing process of top-fermentation, where the yeast rises to the top and is most effective around temperatures of 25-32°C (López et al., 2013).
In this experiment, we tested the differing fermentation rates for yeasts commonly used in brewing beers and wine: S. cervisiae and Pasteur Champagne yeast suspension when placed into a 30°C water bath (Urry et al., 2017. 118). The purpose of this experiment was to investigate the difference in fermentation rates of S. cervisiae and Pasteur Champagne Yeast Suspensions. It was hypothesized that when combined with glucose, S. cervisiae yeast suspension would have a greater rate of fermentation than Pasteur Champagne yeast suspension with or without glucose and S. cervisiae yeast without glucose. Further, it was predicted that if the S. cervisiae yeast was added to a solution containing glucose, then it would ferment at the highest rate as well as accumulate the greatest amount of CO2. This is due to its optimal fermentation rate being at approximately 32°C, which is closest to the water bath temperature of 30°C, as well as containing glucose, an essential element to fermentation (López et al., 2013).
MATERIALS AND METHODS
The differing fermentation rates for yeasts commonly used in brewing beers and wine: S. cervisiae and Pasteur Champagne yeast were tested by creating solutions of varying contents and recording the total CO2 evolved by the different concentrations. The materials used for this experiment included 5 respirometers (5 test tubes, 1-mL graduated pipettes, aquarium tubing, flasks, binder clips), pipette pump, 5-mL graduated pipettes, 3-in donut-shaped metal weights, stopwatch, S. cervisiae yeast suspension, Pasteur Champagne yeast suspension, 10% glucose solution, distilled (DI) water, and a water bath (Urry et al., 2017. 123). Each of the five test tubes contained different amounts of DI water, glucose solution, and yeast suspension, however all test tubes had a consistent total volume of 7 mL. The amount of each substance per test tube is outlined in Table 1, using Microsoft Word, and was measured using graduated pipettes. Each test tube was then placed into a flask filled with enough water to ensure that the flask would not float in the water bath. Solutions were allowed to equilibrate for 5 minutes before creating respirometers, then the respirometers were filled to the 0 mL mark with solution. The initial readings were recorded for each pipette and then the stopwatch was immediately started. From here, at every 2-minute increment, readings were recorded on the 1 mL incremented pipette, until 20 minutes was reached on the stopwatch (Urry et al., 2017. 120-121). Readings were recorded in the actual reading column of Table 2, which was created using Microsoft Word. The actual measurements were then subtracted from the initial (time 0) reading in order to calculate the total CO2 evolved (Urry et al., 2017. 120-121). The results are displayed in Table 2. The total CO2 evolved is depicted in Figure 1, using Excel Software, and is the dependent variable of the experiment, which was measured by the amount of liquid remaining in the pipette. The independent variable was the type of yeast used (S. cervisiae, Pasteur Champagne). Controlled variables include same type of respirometer, same pipettes, same volume per test tube, same 30°C temperature water bath, same stopwatch, same time intervals. These are kept controlled in order to eliminate the chance of confounding variables, or an alternative independent variable. Keeping the conditions the same prevents any misconceptions of where the results are coming from. Controls were created by creating test tubes that lacked one or more of the substances (one without yeast, one lacking glucose and Pasteur Champagne yeast, and one lacking glucose and S. cervisiae) in order to determine which substance was creating an effect on fermentation rates.
Table 1. The Experimental Design of the Test Tubes containing DI Water, S. cervisiae Yeast Suspension, Pasteur Champagne Yeast Suspension, and 10% Glucose Solution
Test Tube Distilled Water (mL) S. cervisiae Yeast Suspension
(mL) 10% Glucose Solution (mL)
1 4 3 0 0
2 4 0 3 0
3 3 2 0 2
4 3 0 2 2
5 4 0 0 3
Test tube 4, containing DI water, Pasteur Champagne Yeast Suspension, and the 10% Glucose solution had the highest rate of fermentation. This is evidenced by the greatest positive difference in CO2 evolved when finding differences between actual and initial readings of CO2 over a 20-minute time span (Table 2). Tubes 2 and 3 also showed small, non-significant positive values of change in the CO2 evolved. Tube 5, which lacked yeast, showed no difference in CO2 evolved, evidencing no change or fermentation. Tube 1, without glucose, illustrated a negative difference in the CO2 evolved, indicating that the liquid level rose.
Table 2. CO2 Evolved and the Change in the Amount of Liquid in each Pipette (in mL) with Solutions of DI Water, S. cervisiae Yeast Suspension, Pasteur Champagne Yeast Suspension, and 10% Glucose Solution
Tube 1 Tube 2 Tube 3 Tube 4 Tube 5
Time (min) Actual (A) mL
CO2 Evolved (A-I) mL Actual (A)
mL CO2 Evolved (A-I)
mL Actual (A)
mL CO2 Evolved (A-I)
mL Actual (A)
mL CO2 Evolved (A-I)
mL Actual (A)
mL CO2 Evolved (A-I)
0 (initial reading) 0.04 0 0.03 0 0.03 0 0 0 0 0
2 0.03 -0.01 0.03 0 0.02 -0.01 0.28 0.28 0 0
4 0.02 -0.02 0.03 0 0.02 -0.01 0.49 0.49 0 0
6 0.02 -0.02 0.03 0 0.20 0.17 0.65 0.65 0 0
8 0.02 -0.02 0.04 0.01 0.30 0.27 0.75 0.75 0 0
10 0.02 -0.02 0.04 0.01 0.35 0.32 0.79 0.79 0 0
12 0.02 -0.02 0.05 0.02 0.40 0.37 0.82 0.82 0 0
14 0.02 -0.02 0.05 0.02 0.48 0.45 0.86 0.86 0 0
16 0.05 0.01 0.08 0.05 0.52 0.49 0.88 0.88 0 0
18 0.05 0.01 0.08 0.05 0.58 0.55 0.90 0.90 0 0
20 0.06 0.02 0.1 0.17 0.62 0.59 0.92 0.92 0 0
Table 2 describes the amount of CO2 evolved (mL)in each of the 5 test tubes of the experiment. In order to find the CO2 evolved, the Initial Reading was subtracted from Actual Reading on the graduated pipette. The change in the amount of liquid was used to measure the amount of CO2 evolved.
Figure 1. CO2 Evolved (mL) By Solutions of DI Water, S. cervisiae Yeast Suspension, Pasteur Champagne Yeast Suspension, and 10% Glucose Solution
Figure 1 describes the amount of CO2 evolved in each of the 5 test tubes of the experiment. The initial volume was recorded at time 0 and the actual volume of the liquids in the pipettes were recorded at 2-minute increments up to time 20 minutes. To find the CO2 evolved, the Initial Reading was subtracted from Actual Reading on the graduated pipette. This chart may be used to determine differing fermentation rates among the different solutions.
In order to test the difference in the fermentation rates among yeasts used in brewing beers and wine, various solutions of with Solutions of DI Water, S. cervisiae Yeast Suspension, Pasteur Champagne Yeast Suspension, and 10% Glucose Solution were created. It was hypothesized that S. cervisiae yeast suspension + glucose would have a greatest rate of fermentation, rather than Pasteur Champagne yeast suspension with or without glucose and S. cervisiae yeast without glucose. After creating the solutions, observing the CO2 evolved helps to determine the differing rates of fermentation. The results illustrate that the highest rates of fermentation, as depicted by CO2 evolved, were in test tubes 3 and 4, one of which contained S. cervisiae Yeast Suspension and the other containing Pasteur Champagne Yeast Suspension (Figure 1). Both test tubes contained glucose, the reactant necessary for fermentation to occur. However, test tube 4, containing Pasteur Champagne Yeast Suspension, had a higher rate of CO2 being evolved. The slope of tube 4 was drastically greater than the remainder of the test tubes, indicating that the Pasteur Champagne Yeast Suspension results in the greatest rate of fermentation (Figure 1). This rejects the initial hypothesis that S. cervisiae Yeast Suspension would have the greatest rate of fermentation. As expected, the test tubes without glucose (tubes 1 and 2) did not have substantial evidence of fermentation. This is evidenced by glucose being a required for anaerobic fermentation to occur. However, an unexpected trend in tube 1 was a negative trend in the CO2 evolved. Instead of fermentation occurring, the amount of liquid in the test tube increased, creating a negative difference. These may be attributed to human error in clamping the aquarium tubing at the initial point of the experiment. Because no glucose was added, these changes in slope/ CO2 evolved may not be attributed to fermentation. Additionally, the constant trend for test tube 5 was expected. This constant trend is denoted by a constant value of 0 for the CO2 evolved. This was expected due to a lack of yeast in the test tube. Yeast is a necessary component of creating the ethyl alcohols and CO2 from sugars such as glucose (Cain et al., 2016. 180-181).
These results indicate that the type of yeast used does influence the rate of alcohol fermentation. The maximum results of fermentation over a span of 20 minutes is illustrated by the highly positive slope of the CO2 evolved for Pasteur Champagne Yeast Suspension. A lack of glucose or yeast in test tubes 1, 2, 5 illustrated that a small or no slope of CO2 evolved, indicating that both glucose and yeast are essential components of fermentation. For future experimentation, this experiment could be conducted using different types of yeast. This could aid the brewing or baking industries in finding the most effective and efficient yeast for their products.
In the production of fermented or alcoholic beverages, it is not until the presence of a sugar, that a yeast begins to conduct fermentative metabolism to ethanol (alcohol) + CO2. Metabolites aid cells to create energy and regenerate NAD+ to power fermentation (Walker 2016). Without NAD+, glycolysis may not be continued, which would cause ethanol production to cease (Cain et. al., 2016. 180). Yeasts are also essential in that they create secondary metabolites. Secondary metabolites can act as distinctive flavors or chemical properties. They produce higher alcohols, carbonyls, etc that help to provide the distinctive taste of wines and beers. The yeast not only aids in the process of fermentation but may be used to provide distinctive alcohol content and sensory characteristics of alcoholic beverages (Walker 2016).
Cain, Michael L, et al., “Introduction to Metabolism.” Campbell Biology, by Lisa A. Urry, 11th ed., Pearson, 2016, pp. 168, 179-181.
Combina, M., et al. “Dynamics of Indigenous Yeast Populations during Spontaneous Fermentation of Wines from Mendoza, Argentina.” International Journal of Food Microbiology, vol. 99, no. 3, 1 Apr. 2005, pp. 237–243., doi:10.1016/j.ijfoodmicro.2004.08.017.
López-Malo, María, et al. “Metabolomic Comparison of Saccharomyces Cerevisiae and the Cryotolerant Species S. Bayanus Var. Uvarum and S. Kudriavzevii during Wine Fermentation at Low Temperature.” PLoS ONE, vol. 8, no. 3, 2013, doi:10.1371/journal.pone.0060135.
Urry, Lisa, et al. “Lab Topic 5: Cellular Respiration.” Principles of Biology Laboratory, Custom Edition for Clemson University ed., Pearson Collections, 2017, pp. 118-125.
Walker, Graeme M, and Graham G Stewart. “Saccharomyces Cerevisiae in the Production of Fermented Beverages.” MDPI, Multidisciplinary Digital Publishing Institute, 17 Nov. 2016, www.mdpi.com/2306-5710/2/4/30.
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