Louis Pasteur was a chemist in France. He was asked to investigate diseases that were caused by microorganisms in liquids. He discovered a process now known as pasteurization which involves heating food to an appropriate temperature that kills most harmful bacteria but causes little change in the taste of the food. Foods that are commonly pasteurized are milk, yogurt, fruit juices, and ice cream.

Try This -

You need adult supervision to complete this activity.

Materials:

• A nutrient broth (fruit juice, thin soup, but avoid meat products)
• Clean glass containers (example: baby food jars)
  
• A cover for two of the containers
  
• A heat source (hot plate, stove burner, microwave oven)
  

Procedures:

Set up four clean jars. Fill each of them half way with your nutrient broth.

2. Heat two of the jars to a boiling point. They need to boil for at least ten minutes. Place a clean lid on one of the jars. Leave the other jar exposed to the air.
3. Now cover one of the unheated jars. Leave the other unheated jar exposed to the air.
4. Be sure to label which jars have been heated and which have not.
5. Never expose the covered jars to air.
6. Observe the jars for two weeks. Record what you see in your science journal.

Analysis:

• Which jar had more microorganisms? Why?
• If you wanted to preserve food in a jar or can, what would you do to it first?
• Why are the results of this experiment so important to people?
• What do you think your results mean?