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Micro-Organisms - There are BACTERIA in my yogurt?

Can you think of any microorganisms that are used in the production of food? (Share with your neighbor some of your ideas.) Fungi in the form of yeast helps bread rise. Other fungi flavor cheese, algae are used in ice cream, puddings, dressings and Jell-O® to help thicken, and bacteria are used to make cheese, yogurt, pickles, sauerkraut, soy sauce, vinegar, and olives. Don’t believe it? Well now is your chance to prove it!

How do you make yogurt? Before you begin make sure you have all the necessary ingredients:


  • Two-ounce containers with lids (you can use previously used yogurt containers, or purchase cups with lids from any restaurant supply store or possibly your school cafeteria)
  • Small insulated "cooler" that will be used as the incubator. Small "lunch tote" coolers work well and many of them come with a container that you can fill with hot water that will surely keep your yogurt warm for the 6-8 hours it will need to incubate.
  • Plain yogurt that contains active cultures. Taste the plain yogurt you plan to use as the starter culture. Your yogurt will have the same taste (Dannon® works well). Making yogurt in your classroom is easy, and really "fool proof" if you follow the recipe and procedure:
  • One cup Powdered milk
  • Two cups very hot water
  • Litmus paper
  • Warm water


  1. Whisk the powdered milk and the two cups very hot water together until dissolved.
  2. Add the two large spoonfuls of active yogurt and whisk until most of the clumps are dissolved. Work quickly; you don’t want the mixture to cool.
  3. Pour the mixture into the cups.
  4. Before placing the containers into an insulated cooler (incubator) for six to eight hours, use one cup to conduct a few simple observations. What is the consistency, pH (use litmus paper), color and smell? Be sure to make these same observations after the incubation period.
  5. Place your containers in your insulated cooler, and fill with enough warm water to go half-way up the outside of your containers. During this incubation period the bacteria will multiply, ingest the milk sugar (lactose), and thicken the milk turning the mixture into yogurt. One work of caution, yogurt will not thicken or will separate if disturbed or bumped during the incubation period so... DO NOT SHAKE THE YOGURT WHILE IT IS INCUBATING!!!! Coagulation (thickening) changes the chemical makeup of protein so it is no longer water protein. In yogurt, protein is coagulated because acid is produced in a warm environment. If yogurt is moved during incubation (before yogurt is set), liquid and solid will separate.
  6. After incubation period, refrigerate, add fruit or other flavorings to the yogurt and enjoy!

Now take a small quiz called, "There are bacteria in my yogurt!"

utah state board of education This Sci-ber Text was developed by the Utah State Board of Education and Utah educators.