Why Milk Sours

A germ found floating in the air attacks a portion of the lactose in the milk, converting it into lactic acid; this, in turn, acts upon the casein (proteid) and precipitates it, producing what is known as curd and whey. Whey contains water, salts, and some sugar.

Milk is preserved by sterilization, pasteurisation, and evaporation. Fresh condensed milk, a form of evaporized milk, is sold in bulk, and is preferred by many to serve with coffee. Various brands of condensed milk and cream are on the market in tin cans, hermetically sealed. Examples: Nestle’s Swiss Condensed Milk, Eagle Condensed Milk, Daisy Condensed Milk, Highland Evaporated Cream, Borden’s Peerless Evaporated Cream. Malted milk — evaporized milk in combination with extracts of malted barley and wheat— is used to a considerable extent; it is sold in the form of powder.