Lactic Acid Fermentation

Yogurt production demonstrates fermentation by Streptococcus thermophilus and Lactobaacillus bulgaricus

Heated milk is inoculated and maintained at a given temperature causing bacteria to grow and ferment lactose, the suger in milk

The bacteria produce lactic acid which causes the milk to coagulate

Food grade containers, washed Food grade thermometer Hotplate Beaker tongs 2 cup of milk 1/3 cup nonfat dry milk 2 table spoons yogurt pH meter

Combine milk with nonfat dry milk and heat in water bath to 87ºC

Hold at that temperature for 10 to 20 minutes

Cool to 46ºC and record the pH of the mixture

Place the plain yogurt in jar and gradually blend in the warm milk

Cover and place in oven or incubator at 45ºC

Allow to stand undisturbed until the mixture is firm when the jar is gently wiggled

This may take as long as 6 to 8 houres