Using Good Bacteria to Make Yogurt

Using Good Bacteria to Make Yogurt
Here’s a great experiment using bacteria in yogurt to make your very own home made yogurt! Making yogurt is a great experiment which shows that bacteria can be helpful rather than harmful. It also makes for a tasty treat once your experiment is complete.

Objectives:
  • To see how yogurt is made and to learn about active cultures.
  • investigate the optimal starter cultures for making yogurt from whole milk.


Experiment Details:
  • Type: Kitchen Science
  • Grades 5-8
  • Difficulty of Project: Easy (Level 2)
  • Cost of Completing Project: $5
  • Approximate Time: 10 hours

What You'll Need
See Video Below!
  • One half gallon of organic milk that is pasteurized.
  • One large glass bowl with a lid that closes snugly with a lid.
  • One 8 ounce cup of plain Greek yogurt with live active cultures.
  • Large metal saucepan.
  • A stove or heating source.
  • A regular heating pad.
  • A small towel.
  • Cooking thermometer.
  • Kitchen utensils: tablespoons whisk.


Step-By-Step Procedure
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STEP 1:
Heat the half gallon of milk to 180 degrees Fahrenheit

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STEP 2:
Turn off the heat source. Leave the thermometer in the milk.
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STEP 3:
Watch the thermometer over the next 15 minutes. When the temperature of the milk hits 110 degrees Fahrenheit, it is ready to be cultured.
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STEP 4:
Remove 8 ounces of milk. Add to this the 8 ounce cup of plain Greek yogurt. Whisk the yogurt into the milk until it is well combined.
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STEP 5:
Combine the mixture into the saucepan. Again, whisk until the mixture is smooth and consistent.
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STEP 6:
Pour the entire mixture of yogurt into the bowl with the lid that seals snugly.
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STEP 7:
Place it on the heating pad and cover it with a towel. Allow the bacteria to grow and make the yogurt for at least 10 hours.
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STEP 8:
Refrigerate and enjoy!
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Observation & Conclusion
The bacteria in the plain yogurt contain bacteria. The bacteria are then put into a new culture and can grow and as they eat the lactose they are converting the milk into yogurt. The more bacteria that grow and proliferate, the more thick and tangy the yogurt will get.
Science Fair Questions
1. Would different types of milk (2%, fat free, whole milk) produce different results?
2. Will flavored yogurt work as a starter culture?
3. Would goat milk, Lactaid, or soy milk produce the same results?
Video Demonstrations
Make your own yogurt!