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Temperature's Effect on the Fermentation of Yeast
Temperature's Effect on the Fermentation Rate of Yeast
The rates of chemical reactions are affected by temperature. The purpose of this experiment was to test the effect of five different temperatures on the rate of carbon dioxide production in yeast by measuring the fermentation rate. Saccharomyces, also known as yeast, is a unicellular, eukaryotic sac fungus and is good for this experiment because of it's characteristic of alcohol fermentation. The group was able to document the carbon dioxide production by measuring the volume, then marked at each of the temperature intervals which were tested at temperatures 25°C, 35°C, 45°C, 55°C, and 65° Celsius. The experiment was conducted by pouring yeast in fermentation tubes, heating each of them at different temperatures, marking the rise of the gas bubbles in the fermentation tubes which indicated carbon dioxide production, pouring the yeast out and filling the fermentation tubes up to the marked line with water, and finally pouring the water into a graduated cylinder to measure the volume which can be used to calculate the temperature coefficient value of Q10 and then graphed to illustrate the rate of carbon dioxide produced at each temperature interval and illustrate the amount of carbon dioxide produced at each temperature. It is important to understand the fermentation rate of yeast so as to accurately determine temperature to achieve the desired effect.
Research on this subject has indicated that with higher temperatures in comparison to room temperature, will cause yeast to produce more carbon dioxide, but at some point the temperature can be too high and destroy yeast cells, causing progressively less carbon dioxide production. The rates of chemical reactions will increase with increasing temperatures, up to a certain point which can be demonstrated by the process of baking bread. Temperature speeds up chemical processes because the atoms move faster, and enzymes are proteins that catalyze chemical reactions and function in optimal environmental conditions although they can become unsustainable when exposed to excessive heat which they were not made to withstand. An example of this is when bacterial cells die at high temperatures because their enzymes have been denatured. We hypothesized that the yeast would produce most carbon dioxide at the median temperature of 45 degrees Celsius because any temperature lower than that would not produce enough and temperatures higher than that would produce too much, causing the bread to sink and the yeast to die because their enzymes become denatured and useless. If we don't heat the bread at a high enough temperature, the yeast will not ferment enough to produce enough carbon dioxide to cause the dough to rise. Contrarily, if we heat the bread on too high of a temperature for the same amount of time, the excessive heat will break chemical bonds and change the enzymes structure into a denatured protein, which has an altered shape that wont allow for it to function as it was originally designed to function. This is what is meant when referred to the temperature of a system. Glucose is mixed with the yeast because it contains the enzymes that will be used for energy to accelerate the chemical reaction that causes the yeast to rise and emit carbon dioxide when it is heated. The purpose for performing this study is to understand the rate of fermentation of yeast cells which can be determined by measuring the amount of carbon dioxide produced at each temperature. By understanding this concept, we can discover the rate at which yeast ferments and control the fermentation process. Since there is no direct way to measure gas, an indirect method must be used. The fermentation rate is measured in ml/min which is the rate of carbon dioxide production that is measured over time spent in a water bath. Water will substitute for the carbon dioxide measure's mark at the conclusion of the experiment and the amount of water in milliliters (measured by the graduated cylinder) will serve as an indirect method of fermentation rate because carbon dioxide is a gas which cannot be measured by means other than indirectly with this experiment.
Materials and Methods
The materials needed to conduct this experiment include 2 yeast packets, sugar culture, five fermentation tubes, water, a wax pencil, a graduated cylinder and four water baths, labeled to each of the temperature intervals to be tested . These materials can be obtained at your local grocery store or at any college laboratory room. Be sure to check the expiration date on the yeast packets to make sure they are fresh and have not expired. We noted the expiration date on our yeast packets was December 2, 2010 which indicates that it is not expired and fresh enough to use in our experiment. Expired yeast can produce inaccurate results. No live subjects were used while conducting this experiment. The experiment was performed in the Tarrant County College South Campus lab Room 1205 on Wednesday, October 7th at 6:00 PM.
To begin our experiment, we labeled five fermentation tubes with our group initials and the following temperatures: 25, 35, 45, 55, and 65 degrees Celsius, with our wax pencil. The 25 degree Celsius fermentation tube is equivalent to room temperature and would serve as the experiment control. Then we added 30 ml of yeast to sugar culture and water to each of the five labeled tubes. We used Grandma's Molasses brand sugar culture and Fleischmann's Rapid Rise brand yeast which is readily found at local grocery stores. This combination is a glucose mixture which is equivalent to a cell concentration of 300,000 cells/cm3 which ensures that there will be enough yeast for the reaction to execute rapidly.
Next, we placed each of the fermentation tubes, excluding the 25°C fermentation tube, in their temperature corresponding water baths for an hour and allowed them to ferment, which is to fill with gas bubbles, until three quarters of the closed end of the tube have filled with carbon dioxide. Then we remove all of the tubes at once and mark the level with the wax pencil before we pour out the yeast and then fill the closed end to the mark with water. After that, we pour the water from each tube separately into the graduated cylinder to obtain and record the volume in milliliters. The water indirectly represents the gas production since it cannot be measured in lab. Divide the volume of the gas produced by the time to calculate the rate of carbon dioxide production. Do this for each of the five water bath temperatures. We also calculated the temperature coefficient of Q10 which can be calculated by dividing the rate of production at temperature, which was obtained by pouring the water from the tubes into the graduated cylinder, by the rate of production at temperature minus 10 degrees (representing the cooler temperature). Our results are represented by the graphs below.
Future experiments could be conducted to clarify areas of doubt by simply repeating the experiment over again many times and perhaps under different conditions, using different temperatures or quantities of yeast. As you can see by the graphed data in the results, our experiment supports the hypothesis that the rate of carbon dioxide would be produced at increasing temperatures up until 45° until it would decrease as enzymes are denatured by excessive heat exposure with the higher temperatures of 55° and 65°. Our hypothesis was also confirmed that the rate of change determined by the coefficient of Q10 stated that temperature had a less substantial effect at increasing intervals. The control fermentation tube of the system was set for the room temperature (25°C) because the control shows as the standard for comparison between the other fermentation tubes that were exposed to heating conditions suspected to play a role in the fermentation process. The coefficient value of Q10 is not calculated for the room temperature interval because it does not have a ten degree lower temperature for comparison. The Q10 is calculated by taking the four intervals and dividing the temperature of each of the fermentation tubes by the lower temperature which is 10° lower. The result is the rate of change of carbon dioxide production.
De Schweinitz, Jean. (2009). Chapter 7. Majors Biology Laboratory Manual, (81-88). Iowa. Kendall Hunt Publishing Company.