Making Yogurt – Lactic Acid Fermentation

žMaking yogurt

žLactic Acid Fermentation      

žIntroduction

žYogurt production demonstrates fermentation by Streptococcus thermophilus and Lactobaacillus bulgaricus

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

žThe bacteria produce lactic acid which causes the milk to coagulate

žMateriales

žFood grade containers, washed

žFood grade thermometer

žHotplate

žBeaker tongs

ž2 cup of milk

ž1/3 cup nonfat dry milk

ž2 table spoons yogurt

žpH meter

žProcedure

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

žHold at that temperature for 10 to 20 minutes

žCool to 46ºC and record the pH of the mixture

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

žCover and place in oven or incubator at  45ºC

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

žThis may take as long as 6 to 8 houres


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