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1 class periods of 45 minutes each
Yogurt production in the classroom acts as a living example of the use of microbes in food production.
Bacteria are simple, one-celled organisms and are among the smallest of all cells. Some kinds of bacteria cause deadly diseases; others are helpful in making food. Buttermilk, cheese, vinegar, and even chocolate are produced through the action of bacteria. Some bacteria cause a chemical change called fermentation. Fermentation changes the taste, smell, and form of animal and vegetable matter.
Yeast used in bread production is an example of a fungus that causes fermentation. Yeast consume the sugars present in the bread dough and use the energy from the sugar for growth and reproduction. When the yeast consume sugar, it is broken down into carbon dioxide gas and alcohol. Little bubbles of carbon dioxide released from the yeast fill the dough and cause it to expand or “rise.” A slice of bread can be examined with the naked eye or with a magnifying glass to see the many small spaces made by the carbon dioxide.
Yogurt is a milk product in which the bacteria streptococcus thermophilous or lactobacillus bulgaricus have been added. Once added to the milk, these bacteria consume the milk sugars and undergo fermentation, much like the yeast in bread. The benefit of having a fermented milk product is that so much acid is produced by these organisms that few other potentially harmful microorganisms can grow in this material.
Although microorganisms can produce diseases, they can also be very beneficial to humans. These benefits stem from their ability to decompose as well as their use in food production. Many kinds of bacteria and fungi (e.g., yeast) are used in the production of food.
Evaluate the answers to the questions in #13 that students recorded in their science journals.