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BISC314: Environmental Microbiology


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LAB #5 and field trip #2: the dairy

Today we will travel on our second field trip - to the Oak Knoll Dairy. There we will hear about how they raise their cows and how they process their milk for cheese making. When we return, we'll use the LAB media to select for Lactic Acid Bacteria in the milk and start our yogurt. LAB's will be cultured at 37 C on MRS media


  • Note, you must come in the day after to place your yogurt in the 4C room!

Yogurt is produced by the metabolic activity of bacteria. The consistency of our yogurt will be determined by the addition of powdered milk (which thickens the yogurt) and the acidification of the milk by the lactic acid bacteria naturally found in the milk.
1. Place 250 ml of milk from the dairy into a 500 ml flask.
2. Add 4% (weight/volume) of powdered milk (10 grams in 250 ml) and blend it into the milk by swirling.
3. Heat the mixture in a water bath to 85C for 20 minutes
4. Cool the milk to 40C in an ice bath. You can tell it's cooled enough because it will feel warm to the touch, but will not be unpleasant to touch
5. Add a hefty spoonful of our yogurt starter culture aseptically
6. Incubate at 40C overnight.
7. In the morning, take your 250 ml flask and place it in the refrigerator (4C)