Fermentation Lab Sheets‎ > ‎Yogurt Fermentation

PURPOSE: To determine the effect of solid content and inoculation rate on the fermentation time of yogurt.


Milk is heated to 85-90°C and held at that temperature for 30 min. After cooling to 45 °C under top water, add inoculum’s, previous day yogurt,

1. Group 1, do not add skim milk powder, inoculum rate 4%

2. Group 2, do not add skim milk powder, inoculum rate 2%

3. Group 3, add 5% skim milk powder, inoculum rate 2%

4. Group 4, add 10% skim milk powder, inoculum rate 2 %

Incubate milk at 42°C for 3 h. Refrigerate samples.


Measure the lactic acid and pH of the milk before fermentation. Do same measurements after fermentation was completed and overnight storage. Discuss the effect of inoculum rate and solid content on the pH and lactic acid production rate clearly.

Research the following topics;

Names of microorganisms used in yogurt fermentation.

What is symbiosis?

Reason of heating milk at 85-90°C for 30 min. Why is it necessary to cool coagulum after


What happens during fermentation of yogurt?

What should be the optimum pH, lactic acid and solid content of yogurt?

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