Yeast is a simple living organism that can break down sugars into ethyl alcohol (ethanol) and carbon dioxide. The process by which yeast breaks down sugars into ethyl alcohol and carbon dioxide is called fermentation.
The tiny gas bubbles rising in the liquid mixture in the bottle are carbon dioxide gas bubbles that are made during the fermentation. The balloon on the bottle expands and becomes inflated because it traps the carbon dioxide gas being produced.
The ethyl alcohol that is made during fermentation stays in the liquid mixture. When fermentation is finished, the liquid mixture usually contains about 13 percent ethyl alcohol. The rest of the liquid is mostly water.
The ethyl alcohol can be concentrated by a process called distillation. During distillation, the liquid fermentation mixture is heated to change the ethyl alcohol and some of the water into a vapor. The vapor is then cooled to change it back into a liquid. This distilled liquid contains 95 percent ethyl alcohol and 5 percent water. The remaining water can be removed by special distillation methods to give pure ethyl alcohol.
In some areas of the United States, ethyl alcohol is blended with gasoline to make a motor fuel known as gasohol. About 8 percent of the gasoline sold in the United States is gasohol.
Gasohol burns more cleanly than pure gasoline. This results in fewer pollutants being released into the air. The use of gasohol as a motor fuel is particularly important in cities that have a lot of smog.
Corn syrup is a mixture of simple and complex sugars and water. It is made by breaking down the starch in corn into sugars. The process is called digestion. In this experiment you changed the sugars in corn syrup using yeast. Much of the ethyl alcohol used to prepare gasohol is made by fermenting corn and corn sugar.
Over one billion gallons of ethyl alcohol are made each year by fermentation of sugars from grains such as corn. Ethyl alcohol is a renewable energy source when it is made by fermenting grains such as corn. This is because the grains, such as corn, are easily grown.
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