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It is a long process, divided into three stages. In the first, called preparation and standardization, the raw material milked from the cows is preheated to 45ºC and placed in a large centrifuge, which separates the fat from the rest of the milk. This fat is then returned to the milk in the desired proportion: 26% in the case of whole milk, zero for skimmed milk. After two pasteurizations (a process that eliminates bacteria), the second stage begins: concentration. In a machine called a tubular concentrator, the milk flows in thin films into a series of tubes through which steam passes. This causes it to lose water and turn into a paste. To get condensed milk, just add sugar. In the case of powdered milk, a last step is necessary, drying: the paste is sprayed in the form of a fine cloud of droplets in a closed chamber, filled with hot and dry air, like a sauna.
By the time the droplets reach the floor, they have already lost most of their water and fall in the form of dust. “Then it is enough to collect and bottle, adding nitrogen gas to prevent the oxidation of the fat”, says food engineer Rômulo Rocha, from a dairy company.