Processing

The steps in a typical dry milk processing operation are as follows:

• Receipt of fresh, high-quality milk from modern dairy farms, delivered in refrigerated, stainless steel bulk tankers.

• Separation of the milk (if nonfat dry milk is to be manufactured) to remove milkfat, which commonly is churned into butter. If dry whole milk is to be manufactured, the separation step is omitted but may be replaced by clarification.

• Pasteurization by a continuous high-temperature short-time (HTST) process whereby every particle of milk is subjected to a heat treatment of at least 71.7°C for 15 sec.

• Holding the pasteurized milk at an elevated temperature for an extended period of time (76.7°C for

25-30 min.)—a step used only in the manufacture of high-heat nonfat dry milk, which commonly is used as an ingredient in yeast-raised bakery products and meat products.

• Condensing the milk by removing water in an evaporator or vacuum pan until a milk solids content of 40% is reached.

• Delivery of the condensed product to the dryer.

Commercial U.S. drying processes are of two types— roller (drum) and spray. The former currently is used only to a limited extent. In this process, two large rollers, usually steam-heated internally and located adjacent and parallel to each other, revolve in opposite directions contacting a reservoir of either pasteurized fluid or condensed milk. During rotation, the fluid milk product dries on the hot roller surface. After approximately three-quarters of a revolution, a carefully positioned, sharp stationary knife detaches the milk product, now in the form of a thin dry

Table 1. Yearly U.S. Production of Dry Milks"

Year

Nonfat dry milk

Dry whole milk

Dry buttermilk

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