The Relationship Between Yeast Fermentation And Food

Concentration Essay, Research Paper

In this experiment different concentrations of sucrose were tested to determine which leads to the most respiratory activity in yeast. Yeast is a heterotrophic anaerobic fungus which lacks chlorophyll. Yeast is used commercially to ferment the sugars of wheat, barley, and corn to produce alcohol, and in the baking industry to raise or expand dough. Yeast or alcoholic fermentation is the anaerobic process of respiration by which sugars, such as glucose and sucrose, are converted into ethanol and carbon dioxide (CO2 ). This process is illustrated in the following equation:


C12H22O11 + H2O —> 4 CH3CH2OH + 4 CO2

sucrose + water (yields) ethanol + carbon dioxide

In order to determine what concentration of sucrose and water leads to the most respiratory activity, ten large test tubes were set with different concentrations by the process of serial dilution. The first test tube was filled with 40 ml of 60% sucrose solution. Then, the nine remaining test tubes were serially diluted, so that the sucrose concentration ranged from 30% to 0.12%.

The hypothesis in this expriment was that the most respiratory activity would take place with 60% sucrose concentration. Since yeast fermentation requires sucrose and water, aproximately equal proportions of both would yield to the most respiratory activity.

Once the sucrose concentration was serially cut to the desired level, the experimenter added 5 ml of yeast suspension to each one of the ten test tubes.

Then, ten small test tubes were placed invertedly into each one of the large test tubes, making sure no air bubbles remained within the small tibes.

The test tubes were left 24 hours, allowing for fermentation to take place. But, no respiratory activity was detected.

In previous experimentation, it was found that yeast fermentation did take place in different molasses concentrations. Since, molasses contains large quantities of sucrose, it was assumed that different concentrations of pure sucrose would yield similar results, when mixed with yeast. However, this was not the case.

The probable explanation is that in order for fermentation to take place, an enzyme is needed to break down sucrose –a disacharide– into glucose and fructose –monosacharides. This enzyme is present in molasses, but it is absent in the sucrose solution.

The Relationship Between Food Concentration, and Respiratory Activity

September 25, 1996


1) Encarta Encyclopedia, CD-Rom Edition, Microsoft, 1994.

2) Biological Science, Prentice Hall, 1983.

3) Grolier Encyclopedia, CD-Rom Edition, Grolier Publishing, 1995.


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