Fermentation in Yeast Experiment

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To demonstrate Alcoholic fermentation (Anaerobic Respiration) in yeast (Saccharomyces cerevisiae)
Anaerobic respiration is a form of respiration that takes place in the cytoplasm of cells and results in the release of energy from the incomplete breakdown of ingested food materials without the involvement of gaseous oxygen. Anaerobic respiration results in the production of intermediate compounds such as lactic acid or alcohol.
Certain bacteria and fungi derive all or most of their enegy from anaerobic respiration and the end products are frequently alcohol and carbon dioxide. The process in this case is called fermentation.
Fermentation is therefore a form of anaerobic respiration which results in the formation of alcohol as respiratory byproduct along with carbon dioxide.
However, fermentation can also refer to those processes that result in the formation of other organic compounds such as citric acid, butyric acid or oxalic acid etc
One of the most widely demonstrated, studied and commercially exploited fermentation processes is the alcoholic fermentation carried out by Yeast cells Saccharomyces cerevisiae
This chemical equation summarises yeast fermentation:
C6H12O6-- 2CO2 + 2C2H5OH + Energy
In this experiment, we’ll demonstrate alcoholic fermentation in yeast cells
For this experiment we’ll need the following:
• A fermentation setup consisting of a large test tube with a tight fitting one hoed rubber cork through which is inserted a delivery tube bent at 90 degrees in two places. One end of the delivery tube reaches a few centimetres into the large tube, while the other end reaches to the bottom of a smaller test tube.
• A clamp stand
• Dry bakers yeast powder
• Glucose powder
• Lime water
• Paraffin liquid or cooking oil
• Boiled and cooled water
• Beakers
• Stirring rods
To begin the experiment, prepare 5% glucose solution by dissolving 5g of glucose powder in 100ml of boiled and cooled water in a beaker.
Also prepare a small quantity of 10% yeast suspension by adding approximately 5g of bakers yeast to 50 ml of boiled and cooled water in a beaker and stirring the contents.
Take the glucose solution and the yeast suspension in a 5:1 ration in the large test tube. So if your taking 50ml of glucose solution, add 10 mls of yeast suspension to it.
Add enough liquid paraffin dropwise along the inner walls of the test tube so that the paraffin completely covers the surface of the glucose yeast solution mixture.
This addition of oil layer is necessary to create a anaerobic environment in the test tube.
Now cover the test tube with the cork containing the delivery tube making sure that the end of the delivery tube lies way above the level of the oil surface.
Now seal the cork using glycerol or grease.
Secure the test tube using a clamp stand
Once the tube has been secured, Introduce the other end of the delivery tube into the smaller test tube containing lime water, making sure that the end of the tube is immersed well below the level of the lime water.
Allow the setup to stand for a few minutes.
After sometime, you’ll begin to notice air bubbles coming out of the end of the dleivery tube submerged in the lime water.
You’ll also start to notice a buildup of a frothy layer on top of the oil layer in the large test tube.
After several minutes, the lime water begins to turn cloudy white suggesting that the gas bubbles coming out from the delivery tube could potentially be carbon dioxide, one of the byproducts of fermentation.
At this point, disassemble the setup. First take the tube containing lime water and add 1% hydrochloric acid dropwise to the tube and gently shake. The cloudy white precipitate dissolves completely suggesting that the white precipitate is indeed calcium carbonate, a product of the reaction bewtten carbon dioxide and lime water which is calcium hydroxide solution. Calcium carbonate readily dissolves in a mineral acid, in this case hydrochloric acid, to form its corresponding soluble salt, in this case calcium chloride solution.
Now take the large test tube and smell the contents. You’ll find that it has a stong ethanolic smell suggesting that ethanol is also produces as one of the byproducts during the fermentation of the glucose solution by yeast cells in the suspension.
This experiment therefore demonstrates alcoholic fermentation by yeast cells to produce carbon dioxide and ethanol as fermentation byproducts.
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