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Biology LibreTexts

13.5: Activity – Yogurt Production

  • Page ID
    24210
  • Yogurt Production

    Procedure

    1. Place beaker on hot plate. Add 300 mL of milk.

    2. Measure and record the pH of the milk using pH indicator paper.

    3. Insert thermometer into milk and gently heat while stirring. Bring the milk to 85°C.

    4. Remove milk from the hot plate and allow to cool to 43°C.

    5. Measure and record the pH of the cooled milk using pH indicator paper.

    6. Measure 50 mL plain yogurt. (This yogurt must be marked as containing live yogurt cultures).

    7. Slowly add the yogurt to the in the cooled milk, be sure to thoroughly mix the ingredients to create a homogenous solution. Adding about 30 ml (1/8 cup) nonfat dry milk at this time will increase the nutritional content of the yogurt. The yogurt will also thicken more easily.

    8. Measure and record the pH of the mixture using the pH indicator paper.

    9. Place the mixture into a glass jar.

    10. Incubate the mixture in an incubator or water bath at 30 - 32 °C for 5 - 6 hours

    11.  Place the yogurt in a refrigerator for 24 hours. Measure and record the final pH using pH indicator paper. 

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    Questions for Review

    1. What is the function of heating the milk in step 3.
    2. What is the purpose of adding the yogurt to the cooled milk in step 7?
    3. What attributes does lactic acid confer to yogurt?
    4. How does the consistency of the milk change during the production of yogurt? What facilitates this change?
    5. What are the breakdown products of lactose?
    6. Go to the CDC website (http://www.cdc.gov/foodsafety/outbreaks/) and describe one of the Selected Outbreak Investigations that occurred over the last 2 years.