Ethanol fermentation is a system in which hydrogen ions from NADH + H+ are broken down in order to release the trapped energy and regenerate NAD+. In the absence of a mitochondria or oxygen ethanol is formed, which is typically found in bacteria and some yeast. Yeast fermentation has been used commercially since the 18th century to brew alcohol, when French chemist Antoine Lavoisier found that in an experiment when he added sugar to the reaction. Lavoisier found that when he added the sugar to the reaction two-thirds of the sugar ended up producing alcohol and the other third was oxidized and became waste in the form of CO2 (This is why there is foam produced on top of most beers). By 1780 yeast was fermented in order to bread which was sold commercially by the Dutch. Yeast fermentation has been used for a prolonged period of time, and through extensive research, factors have been found that effect the process of yeast fermentation. Such factors include the amount of saccharide used and the type of saccharide, both of these factors will be put through a test in order to draw conclusions. The CO2 waste from the fermentation process will be examined, by measuring the pH of reaction, lower pH means more CO2 production.
The first factor being measured is the type of sugar used in the fermentation of yeast. The types of sugar being used in the experiment is glucose, sucrose, and lactose. Glucose is a monosaccharide and is used in the first step of glycolysis in order to help create pyruvates, which are then used to create ethanol as long as there is no mitochondria or oxygen present. Sucrose is a disaccharide, commonly referred to as sugar, it’s used worldwide, and mainly harvested from sugarcanes. Sucrose is composed of two monosaccharide’s being; glucose and fructose, both are used in glycolysis in order to produce pyruvate. The final sugar being tested is Lactose, a common sugar used worldwide in milk and other dairy products. Lactose is a disaccharide made up of glucose and galactose, and this structure will make it less effective in fermenting yeast.
The second factor that will be measured in this experiment is the amount of sugar used in yeast fermentation reaction. The amount of sugar will greatly affect the yeast fermentation process because with less sucrose there will be a short supply of glucose molecules for the yeast to ferment with and as a result pH levels will not drop as much due to less CO2 being production.
Materials:
pH Probe
Lab Quest
1.75g of sucrose
300 mL of 40°C water
Metal Stand with clamp
3.0g of yeast
100 mL Graduated cylinder
Beaker
Hot Plate
Scoopula
Balance
Erlenmeyer flask
Tap Water
5 cm x 5 cm x 1cm paper container
Procedure: (Refer to Emma Henry’s lab for procedure of type of sugar) 1. Plug pH probe into Lab Quest.
2. Plug the lab quest into the nearest electric outlet.
3. Remove storage solution from the pH probe.
4. Place the pH probe into the clamp on the metal stand.
5. Fill a beaker with tap water and place it under the pH probe. 6. Lower the pH probe until the pH probe is three-quarters inside the beaker of water. 7. Swirl the beaker full of water until Lab Quest approximately reaches a pH of 7. 8. Pour 100 mL of 40°C water into a graduated cylinder.
9. Use the scoopula to pour and measure 1.0g of yeast onto the balance. 10. Place the 1.0g of yeast onto the 5 cm x 5 cm x 1cm paper container. 11. Use the scoopula to pour and measure 1.0g of sucrose onto the balance. 12. Place the 1.0g of sucrose onto the 5 cm x 5 cm x 1cm paper container 13. Pour the 100 mL of 40°C water from the graduated cylinder into the Erlenmeyer flask. 14. Pour the 1.0g of sucrose into the Erlenmeyer flask.
15. Place your thumb on the top opening of the Erlenmeyer flask and swirl until the sucrose has finished being dissolved. 16. Raise the clamp with the pH probe and remove the beaker from underneath, and pour the water out into the sink. 17. Place the Erlenmeyer flask under the clamp with the pH probe. 18. Lower the clamp so that the pH probe is three-quarters inside the Erlenmeyer flask. 19. Gently swirl the Erlenmeyer flask until the pH hits approximately 7. 20. Pour the 1.0g of yeast into the Erlenmeyer flask.
21. Carefully swirl the Erlenmeyer flask and record the initial readings. 22. Start timer.
23. Record the pH every 30 seconds for 8 minutes.
24. Repeat steps 5 – 23 for 0.5 grams of sucrose.
25. Repeat steps 5 – 23 for 0.25 grams of sucrose.
26. Turn off Lab quest.
27. Unplug pH probe from the Lab Quest.
28. Place storage solution back onto the pH probe.
29. Place both the Lab Quest and pH probe in their respective box. 30. Clean up all materials.
Analysis of Factor 1 (Mass of Sucrose):
Through examining all three of the trend lines for the masses of sucrose, each of them should a drop in pH over time, but the greater the mass of the sucrose the greater release of CO2, which resulted in lower drop in pH. This is proven by analyzing the slope of each mass, in 1.0g of sucrose the, the results showed that the pH dropped 0.003 per second. In 0.5g of sucrose the result of the slope showed the pH dropped 0.0027 per second. Lastly the 0.25g of sucrose showed that the pH dropped 0.0026 per second. Therefore with greater mass of sucrose in the fermentation of yeast, the greater the production of CO2 in the reaction, resulting in lower pH levels. Throughout the experiment there were sudden drops and gains in the mean of the pH, which could have been cause by the pH probe not put far enough into the Erlenmeyer flask, and when corrected the pH had a sudden drop. In conclusion the final results of pH from the lab were as expected in 1.0g having the lowest pH (5.87), 0.5g having the 2nd lowest pH (6.01), and 0.25g had the highest pH (6.18). Explanation of Factor 1 (Mass of Sucrose):
The reasoning behind these results is simple, with a larger amount of sucrose that means there is a greater supply of glucose molecules. As seen in the graph with a greater mass of sucrose, more CO2 was produced, and this is a result of more sucrose being available for the enzymes involved in fermentation reaction to breakdown into glucose and fructose. The glucose molecule would go through glycolysis, were the fructose molecule would skip a step and be further broken down to make a pyruvate. The pyruvate then removes a CO2 and breaks down NADH + H+ to NAD+ to create ethanol. With greater mass of Sucrose results in a prolonged period of time in which the sucrose is being continually broken down, were as with a lower mass of sucrose results in a shorter period of time in which the sucrose is being converted to ethanol. Therefore with a greater mass of sucrose, it results in longer amount of time in which CO2 is being released, in which pH also drops. Analysis of Factor 2 (Type of Sugar):
Analyzing the results of the trend lines from the graphs of the three different types of sugar, the results showed that sucrose produced the most CO2 over the period of time. Lactose had the lowest rate of CO2 production, and these results are proven by the slope of each of the graphs. Sucrose had the highest slope (0.0044 pH/sec), the 2nd highest was glucose (0.0042pH/sec) and the lowest slope as mentioned before was lactose (0.0032 pH/sec). Also examining the final pHs of each of the sugars, glucose had a pH of 6.09, sucrose had a pH of 5.79 and lactose had a pH of 6.51, and this further proves that sucrose was the most efficient in producing ethanol through yeast fermentation. Therefore according to the results of the graph sucrose fermented yeast the most efficiently, then glucose and finally lactose. Explanation of Factor 2 (Type of Sugar):
Of the three types of sugars, sucrose fermented the best, and this was quite
unexpected until you look at the reaction molecularly. Sucrose is a disaccharide which is made of glucose and sucrose, and this is what make sucrose a more efficient molecule to be fermented then glucose. Although it may take longer to breakdown the sucrose in order to get the glucose molecule it is made up with the fructose, since the fructose is symmetrical it skips a step in glycolysis this means it will be converted to pyruvate quicker than a glucose since it is easier to breakdown. Since the sucrose will now produce twice as many pyruvate molecules which are later converted to ethanol, this means twice as much CO2 is produced, as a result lower pH levels. Glucose is easily fermented because it is a monosaccharide that goes into glycolysis without breakdown of a molecule and this benefits the rate of CO2 produced, but it does not produce as much pyruvate as sucrose and the fructose in sucrose skips a step in glycolysis. Lastly Lactose just like sucrose is a disaccharide but in lactose it only produces on molecule useful in glycolysis, that being glucose the other molecule galactose cannot further be used in fermentation process. Therefore sucrose will produce the most CO2 out of the three types of sugars due to its complex structure, then glucose since there is no breakdown needed, finally lactose because it needs to be broken down and it only produces one glucose that can be used in the fermentation reaction. Errors and Improvements:
While conducting this experiment there were a few errors in the lab that could have been corrected in order to have a perfect lab. A major error in the lab was the pH probe during the experiment was up to high in the Erlenmeyer flask and this effected the pH we got due to a number of factors inside of the flask that could have changed the pH. Once the pH probe was put in properly the readings went followed the trend line better, but this was not corrected until it was halfway through the experiment. To ensure that the problem would not occur again, the pH probe should be place ¾ of the way into the Erlenmeyer flask before recording data.
Another issue in the lab that could have affected the results was inconsistent swirling of the flask before each measurement of pH level. This would greatly affect the results of the lab because if the flask is not consistently swirled correctly this could result in fluctuated pH readings. The inconsistent swirling caused the results of the pH to be inconsistent with the trend line and resulted in bad readings. For the future this could have been avoided by setting a consistent time before each swirl in order to get fair reading of the pH. Another error in this lab would have been the temperature of the water since the waters temperature was not consistently measured, and since the water could have been colder in one of the experiment then the other this could have affected the fermentation because enzymes work better in hotter temperatures and if one is colder than the other this would mean the fermentation could have been less efficient. . This error could be fixed by consistently measuring the temperature of the water to make sure that they are all same in order to get fair results.
The final error in the lab that could have been avoided was inconsistent amounts of yeast. Since paper containers were used to hold and pour the yeast into the flask not all the yeast got into the flask, and the mass of yeast fluctuated a lot. With false amounts of yeast in the reaction this would change the pH reading due to inconsistent CO2 production. This problem could be fixed by using a very precise tool to pour yeast into, and that could easily be used to pour into an Erlenmeyer flask.
Conclusion:
In conclusion, through this lab it can be said that with greater masses of sucrose, yeast will ferment more efficiently and last longer and as a result produce more CO2. Also sucrose will produce the most amounts of CO2, due to its molecular structure which contains a glucose and a fructose, then followed by glucose since it goes straight into the glycolysis, and last was lactose since it will take more time to break down the molecule into glucose and the other molecule produced, galactose, is a waste product.
Works Cited
“Growing Yeast: Sugar Fermentation.” Education.com. N.p., n.d. Web. 29 Oct. 2013. . – How type of sugar effects the fermentation of yeast
“THE EFFECT OF DIFFERENT SUGARS ON THE RATE OF FERMENTATION IN YEAST.” EBSCO HOST. N.p., n.d. Web. 28 Oct. 2013. . – Why Sucrose ferments better then glucose
“Yeast.” Wikipedia. Wikimedia Foundation, 27 Oct. 2013. Web. 29 Oct. 2013. . – How the Dutch used yeast fermentation commercially.
“Yeast Fermentation.” Baking recipes. Learn to bake. Baking help.. N.p., n.d. Web. 29 Oct. 2013. . – How amounts of Sucrose effect yeast fermentation
“Yeast Fermentation and the Making of Beer and Wine.” Nature.com. Nature Publishing Group, n.d. Web. 29 Oct. 2013. . – Found out the history of yeast in brewing – Found out about the French Scientist
