Note from Ricardo
Fermentation of milk into yogurt
Fermentation is not solely for beer and wine. Milk also can be transformed by the action of the great microorganisms. Here is how: bacteria, or "lactic ferments”, which are added to convert the milk lactose (a sugar found naturally in milk) into lactic acid. After 4 to 6 hours of fermentation at a temperature of about 45 °C (110 °F), enough lactic acid is produced to curdle the milk protein called casein. Destabilized by the presence of lactic acid, casein attach together to form a more or less firm gel. The bacteria also produce a host of other substances that change the flavor and texture of the milk. The types of bacteria selected by manufacturers and the fermentation conditions affect the intensity of the sour taste and texture of the yogurt, which can be firm or runny. The bacteria most often used are Streptococcus thermophilus and Lactobacillus bulgaricus.