Factors That Affect Yeast Fermentation

Kendal Newman

Bio 1C – 8 am

Ernst

Factors that Affect Yeast Fermentation

Introduction

        For thousands of years humans have been using the process of yeast fermentation to produce bread, alcoholic beverages, and more recently fuel. When access to oxygen is decreased, some fungi – like yeast – use the process of alcoholic fermentation (Ho 2010). This common procedure is achieved through the process of glycolysis, a series of reactions in which glucose is broken down into pyruvate, which is then further deconstructed into ethyl alcohol (ethanol) and Carbon Dioxide (Ho 2010). In our experiments, we tested the ability of yeast to ferment in different situations.

        In experiment one we tested the rate of fermentation in different concentrations of glucose. Theoretically, if you have the same amount of reactant one – in our case, the yeast - the reaction should occur at a faster rate in the presence of a higher concentration of reactant two – the glucose solution. Therefore, if you have a higher concentration of the glucose solution, there will be a greater amount of the product – Carbon Dioxide – produced at a much faster rate. I believe that the tube containing the higher concentration of glucose will produce the most carbon dioxide in the twenty minute time span.

        In experiment two we tested the ability of yeast to ferment in differing amounts of ethanol and soap solutions. Though ethanol is a product of fermentation in yeast, ethanol concentrations that are too high can lead to poor growth and eventually cell death, limiting the fermentation output in a situation known as ethanol toxicity (Carmona-Gutierrez, Sommer, Andryushkova1, Kroemer, & Madeo 2012). Many studies have been conducted to try and prove that having a higher concentration of lipids can prevent an organism from experiencing ethanol toxicity (You, Rosenfield, & Knipple 2003; John, Littleton, & Jones 1980). In our second experiment, we wanted to test this theory. We believe that by adding soap to a yeast & glucose solution containing ethanol will counteract the effects of ethanol toxicity and allow for a regular production of Carbon Dioxide. Therefore, tubes two and three will produce carbon dioxide.

Materials & Methods

        In experiment one, we started with four flasks, each filled with enough water to keep them submerged in a water bath (about 5-7cm from the top of the flask). They were labeled 1, 2, 3, 4 and a metal ring was placed around the neck to keep them stabilized in the bath. Next, four test tubes were also labeled 1, 2, 3, and 4. Tube “1” was filled with 4 mL of deionized water and 3 mL of glucose suspension. Tube “2” was filled with 6 mL of deionized water and 1 mL of yeast suspension. Tube “3” was filled with 3 mL of deionized water, 1 mL of yeast suspension, and 1 mL of glucose suspension. Lastly, tube “4” was filled with 1 mL of deionized water, 3 mL of yeast suspension, and 3 mL of glucose suspension. The tubes were placed in their corresponding flask, and these were all placed into a water bath set to 30°C. They were allowed to equilibrate for five minutes.

        After five minutes, a 1 mL graduated pipet with a piece of attached aquarium tubing was placed into each test tube. A pipet pump was attached to the free end of the tubing on the first pipet and used to draw up the fermentation solution into the pipette just above the 0 mL line marker. It was then clamped shut. The clamp was released slowly to allow the solution to reach the 0 mL line marker (or just below the marker). This step was repeated for the remaining three tubes. The initial readings for each pipette were recorded, and then sequential readings were taken every 2 minutes for the following 20 minutes to keep track of how much Carbon Dioxide was being produced. Results were collected for the entire class and the pooled data was used in the results section of this paper.

        For experiment two we again started with four flasks, each filled with enough water to keep them submerged in a water bath. They also were labeled 1, 2, 3, 4 with a metal ring placed around the neck to keep them stabilized. To create our soap solution, we dissolved 0.10 grams of olive oil based soap into 3 mL of ethanol. The solution was heated in a hot water bath to dissolve the soap completely. Next, four test tubes were also labeled 1, 2, 3, and 4. Tube “1” was filled with 3 mL of yeast suspension, 3 mL of glucose suspension, and 1 mL of ethanol. Tube “2” was filled with 3 mL of yeast suspension, 3 mL of glucose suspension, 0.75 mL of ethanol, and 0.25 mL of soap solution. Tube “3” was filled with 3 mL of yeast suspension, 3 mL of glucose suspension, 0.5 mL of ethanol, and 0.5 mL of soap solution. Tube “4” was filled with 3 mL of yeast suspension, 3 mL of glucose suspension, and 1 mL of soap solution.