Abstract
Yeast fermentation is a form of alcohol fermentation that occurs at an optimal temperature allowing the cells to produce Adenosine triphosphate (ATP) which in result also produces ethanol and carbon dioxide as waste products. This is an anaerobic process that does not require oxygen to transpire. The central question for this experiment was, what is the effect of temperature on anaerobic fermentation in Saccharomyces cerevisiae? The hypothesis was that when the temperature leaves the optimal range, the fermentation rate would either decrease or seize completely. It was predicted that if the temperature was either too low or too high, then fermentation of the yeast would halt therefore producing very little to no carbon dioxide. To perform the experiment, a solution of yeast and 2% glucose was placed in four different temperatures. The tubes of solution were removed after 30 minutes and the carbon dioxide was then recorded in each of the tubes. The 4 °C solution produced 0.07 mL of CO2, while the 65 °C solution produced 0.95 mL. The room temperature, 23 °C produced 2.18 mL and the 37 °C yeast solution produced 3.32 mL. It was concluded that there is an optimal temperature range for growth of yeast and that if the temperature was too high or too low, the yeast would not ferment, thus not producing any carbon dioxide.
Introduction
The first step in cellular respiration is glycolysis, which is where glucose is converted to pyruvic acid. The next steps depend on whether oxygen is present; when it is not present the two pyruvic acid molecules produced from a single glucose molecule start a process known as fermentation (Reece et. al, 2014). Fermentation is a metabolic process in which an organism converts a carbohydrate, such as starch or a sugar, into an alcohol or an acid (Helmenstine, 2017). Cells go through this anaerobic process to produce a small amount of Adenosine triphosphate (ATP) which is an essential molecule in a cell (AARC Biology Faculty, 2017). Saccharomyces cerevisiae (yeast) produces ethanol and carbon dioxide as waste products through the alcoholic fermentation method (Alba-Lois and Segal-Kischinevzky, 2010). In the early 1950s, scientists White and Munns studied the influence of temperature on yeast growth and fermentation, which led to the discovery that there is an optimal temperature for yeast to grow (White and Munns, 1951). Today fermentation is used to make all sorts of foods and beverages such as, beer, wine, kombucha, kefir, bread, yogurt, and many more.
The preformed experiment was carried out to determine what effect temperature would have on anaerobic fermentation in Saccharomyces cerevisiae. The hypothesis was that when the temperature leaves the optimal range, the fermentation rate would decrease or yield completely. The reasoning for this is based on the knowledge that yeast does not grow in an environment that is too cold and anything too hot will kill the fungus. The hypothesis can be tested by preforming an experiment using four different temperatures, 4 °C, 23 °C, 37 °C, and 65 °C. If the yeast and 2% glucose solution was placed in a 4 °C cold room, then the yeast would not ferment. If the solution was placed in either room temperature, 23 °C or human body temperature, 37 °C, then the yeast solutions would produce carbon dioxide indicating that fermentation had taken place. If the solution was placed in an incubator set at 65 °C, then the heat would kill the yeast thus preventing fermentation from taking place.
Materials and Methods
To prepare the yeast solution, 1 gram of Fleischmann’s Rapid Rise instant yeast was added to 100 mL of a 37 °C, 2% glucose solution. This solution was placed in room temperature for 45 minutes to “wake up” the yeast. Four individual fermentation tubes were labeled with the temperatures, 4 °C, 23 °C, 37 °C, and 65 °C. Fourteen mL of the yeast solution were then added to each of the fermentation tubes. The ends of each of the tubes were plugged using a cotton ball to restrict air for the anaerobic process to work. After the tubes were plugged, they were tipped over to remove the air bubbles in the calibrated chamber of the tube. Once each tube was rid of any more air bubbles, they were each placed into their appropriate temperature settings. Putting them into different temperatures was done to determine whether temperature effects fermentation of yeast. The room temperature tube was left on the lab bench, the 37 °C and 65 °C tubes were both placed into incubators, and the 4 °C tube was placed in a cold room. The time each tube went into their designated temperature was recorded. Each of the tubes were taken out after 30 minutes and the volume of CO2 was measured in the calibrated chamber of the tube. The data the was collected for each separate tube was recorded and graphed.
Results
When observing the results of the experiment, it is evident that temperature effects the production of carbon dioxide in yeast. Table 1 below indicates; the production of CO2 was very minimal. A mere 0.07 mL was produced at the lowest temperature of 4 °C. The next temperature, 23 °C was significantly higher, reaching 2.18 mL. Figure 1 also, shows that the biggest spike was at the mid-range temperature of 37 °C that reached 3.32 mL. The last temperature tested was 65 °C which produced only .95 mL as the table below indicates.
Table 1. Production of Carbon Dioxide at Four Temperatures in Saccharomyces cerevisiae.
Temperature (°C) CO2 volume in mL
4° 0.07 mL
23° 2.18 mL
37° 3.32 mL
65° 0.95 mL
Figure 1. Production of Carbon Dioxide at Four Temperatures in Saccharomyces cerevisiae.
Discussion
The purpose of this experiment was to see if change in temperature affected the anaerobic fermentation process in yeast. The hypothesis for this was that the production of carbon dioxide would slow or completely seize when the yeast solution was not at optimal temperature. If this was accurate, then the yeast solution in the coldest and hottest environments would not ferment. The solution in the optimal (mid-range) temperature would produce carbon dioxide.
The change in temperature undoubtedly influenced the production of carbon dioxide as shown in Figure 1. This supported the original hypothesis that the production of yeast would be more evident in the optimal temperature range.
As predicted, the lower temperature of 4 °C showed barley any trace of CO2 bubbles. This is due to the yeast not having enough energy (heat) to start the process. The two highest production rates that were recorded was for the temperatures of 23 °C and 37 °C. As shown in Table 1, the room temperature solution produced 2.18 mL of carbon dioxide while the human body temperature of 37 °C produced 3.32 mL of CO2. This discernibly indicates that 37 °C is the closest to the optimal temperature for yeast fermentation. The highest of temperature of 65 °C only produced .95 mL of carbon dioxide as the environment for the solution was too hot and did not allow the yeast to ferment but rather killed it. As mentioned earlier, this leads to believe that there is an ideal temperature for yeast fermentation (White and Munns, 1951). In the future, more research could be done to find what the optimal temperature for yeast fermentation is, using a different kind of sugar to compare whether it is more effective than glucose.
Literature Cited
Alba-Lois, L. & Segal-Kischinevzky, C. 2010. Beer & Wine Makers. Nature Education 3:17.
ARCC Biology Faculty. 2017. Biology Laboratory Manual Fourth Edition. Hayden-McNeil Macmillan Learning, Plymouth, MI, 248 pp.
Helmenstine, A.M. 2017. What is Fermentation. Thought Co. https://www.thoughtco.com/what-is-fermentation-608199. Accessed 22 March 2017.
Reece J.B, Urry L.A, Cain M.L, Wasserman S.V, Minorsky P.V, Jackson R.B. 2014, 2011, 2008. Campbell Biology, Tenth Edition. Pearson Learning Solutions, Boston, MA, 499 pp.
White, J. and Munns, D. J. 1951. Influence of Temperature on Yeast Growth and Fermentation. Journal of the Institute of Brewing, 656 pp.