Does Yeast Affect the Decomposition of Apples and Bananas?

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Decomposition is one of nature's dominant forces. Everything decomposes naturally, through bacteria, fungi, insects and other forces, including temperature, oxygen and carbon dioxide levels. During decomposition, which is nature's recycling process, decomposing organisms are converted to fuel and fertilizer, benefiting the environment. The decomposition process can be delayed, or increased, by adding or subtracting certain elements, including yeast, which acts as a catalyst in the decomposition process.


Yeast

Yeast is a simple, one-celled organism, that is a member of the fungus family. Although there are more than 1,000 different types of yeast, the most widely used is Saccharomyces cerevisiae, common in baking and alcohol fermentation. Often used to break down sugars into carbon dioxide, yeast is a mover and shaker in the decomposition process because it is a catalyst, speeding decomposition's chemical reactions.
Apple and Banana Decomposition
Apples and bananas decompose at different rates. Normally, when yeast is added, fruits with higher sugar contents decompose faster. Apples have 32 grams of sugar, versus a banana's 17 grams. However, bananas decompose faster because apples are slightly acidic, with the acid slowing the decomposition rate.

The Experiment

A school science experiment can test yeast's effect on apples, bananas or different fruit juices. The experiment places apple and banana slices into separate plastic bags, some containing 1/2 teaspoon of dry yeast and others without. The bags are then sealed, labelled and allowed to sit. Some experiments vary temperature, placing bags in the refrigerator, outside or on a counter. Results are usually obtained within four days, and the apples and bananas with yeast added decomposed quicker than those without. Similarly, those in warmer locations decomposed faster than those placed in cooler settings, as temperature affects yeast's productivity.

The Results

The apples and bananas with yeast added decompose faster, because yeast feeds on them. According to "The Yeast Beast," by Liane D'Allesandro of Haverford College, "The reason that the banana with yeast decomposes (ripens) much more quickly than the control banana is that yeast is an organism classified in the fungi group. Since this group of organisms does not contain chlorophyll, as green plants do, they cannot make their own food. Therefore, they rely on other sources for their food." As yeast feeds on the sugars contained within the fruit, the yeast causes fermentation, converting sugar into ethyl alcohol and carbon dioxide.

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