Chapter III: Manufactured Milk Products as Related to Ice-Cream

Besides the milk and cream, several other manufactured milk products are used in ice-cream. What has been said previously about the milk and cream applies also to the milk for these products. The quality, especially the flavor, is very important.

CONDENSED AND EVAPORATED MILK

There is a difference between condensed and evaporated milk, but because of their similarity, both in composition and manufacture, they will be considered together. Condensed milk usually has sugar added to preserve it, although some ice-cream-makers use it without added sugar, when it is known as plain in contrast to sweetened condensed milk. The evaporated milk is usually sterilized in sealed cans to preserve it, no sugar being added. More condensed milk is employed in making ice-cream than evaporated milk. The condensed is usually shipped to the ice-cream manufacturer in bulk, either in milk-cans or barrels.

=17. Method of manufacture.=--The water is removed from the milk by heating under reduced pressure. The heating is usually done in a copper pan. (Fig. 5.) This is accomplished by means of a steam jacket on the bottom and usually one or two steam coils in the pan. Before drawing the milk into the pan, it is heated in an open copper vessel, by turning direct steam into the milk. This container is called the hot well or fore warmer. The temperature varies according to whether plain or sweetened condensed is being made. The sweetened is heated higher to dissolve the sugar. The object of heating under reduced pressure is to reduce the boiling point. At ordinary pressure milk would boil at the same temperature or a little above that of water. At this temperature the milk could not be condensed without imparting a pronounced cooked flavor and caramelizing a part of the sugar.

The vacuum in the pan is produced by means of a vacuum pump. A vacuum equal to a column of mercury about 25 inches is usually maintained. The condenser is located at the top of the pan and is directly connected with it. As the milk boils, the vapor passes from the pan into the condenser. In the latter the vapor comes in contact with a spray of cold water which causes it to condense. The pump carries off the condensing water and the condensed vapor. When the desired density is reached, the milk is drawn from the pan and cooled. The proper concentration of the milk is determined by a special graduated scale known as the Baumé. A more recent method is an electric resistance. If sweetened condensed is being made, the sugar is added to the milk, the mixture of sugar and milk are heated to dissolve the sugar before drawing them into the pan.

Sometimes the milk is superheated; this consists of turning live steam into the milk just at the time that the desired concentration is reached. It gives the condensed milk more of a “livery” appearance, which is probably due to the precipitation of the albumen.

The length of time required for condensing the milk to the desired consistency varies with the amount of milk in the pan, amount of heating surface, size and capacity of vacuum pump, and amount and temperature of water in the condenser.

=18. Standards for condensed milk.=--The following standards are given by the United States Department of Agriculture:[9]

[9] Office of the Secretary, U. S. Dept. Agr., Food Inspection, Decision 170, 1917.

“Sweetened condensed milk, sweetened evaporated milk, sweetened concentrated milk, is the product resulting from the evaporation of a considerable portion of the water from the whole, fresh, clean, lacteal secretion obtained by the complete milking of one or more healthy cows, properly fed and kept, excluding that obtained within fifteen days before and ten days after calving, to which sugar (sucrose) has been added. It contains, all tolerances being allowed for, not less than twenty-eight per cent (28.0 per cent) of total milk solids, and not less than eight per cent (8.0 per cent) of milk fat.

“Condensed skimmed milk, evaporated skimmed milk, concentrated skimmed milk, is the product resulting from the evaporation of a considerable portion of the water from skimmed milk, and contains, all tolerances being allowed for, not less than twenty per cent (20.0 per cent) of milk solids.

“Sweetened condensed skimmed milk, sweetened evaporated skimmed milk, sweetened concentrated skimmed milk, is the product resulting from the evaporation of a considerable portion of the water from skimmed milk to which sugar (sucrose) has been added. It contains, all tolerances being allowed for, not less than twenty-eight per cent (28.0 per cent) of milk solids.”

Condensed or evaporated milk should be purchased only on its composition, both fat and solids not fat. For method of testing, see