The principal foods derived from milk which are in common use are:

1. Condensed milk. 2. Cream. 3. Butter. 4. Buttermilk. 5. Cheese. 6. Whey.

1. Condensed Milk

Condensed milk is prepared by slowly evaporating the water of milk by moderate heat in vacuo to the consistence of honey. There are two varieties: the "plain," which is condensed to about one fourth of its bulk and superheated, and to which little or no sugar is added; a stronger, more condensed sort, with which cane sugar is mixed in excess. Such milk yields from 39 to 48 per cent of sugar among its solid ingredients, but sometimes as much as 75 per cent is added. A good deal of the Swiss condensed milk sold in market, as well as that made in this country, contains 40 per cent of sugar.

The sugar prevents fermentation and decomposition, and when condensed milk is put up while hot in hermetically sealed tin cans it will keep fresh for years. It will even remain fresh for several days after a can is opened. It is soluble in water added to any degree of dilution. Condensed milk is largely used for the nourishment of infants, especially among the poorer classes. They thrive upon it for a time, occasionally even better than on raw milk, and it makes them fat, owing to the extra sugar which it contains. It does not constipate, and may be even slightly laxative. But although such babies may appear robust, their flesh is not firm, they develop poorly, are unable to resist disease, and become rhachitic.

Condensed milk should be diluted ten times for a child a month or two old, and cream should be added in liberal proportion.

The formula recommended by Starr is:

Condensed milk........................................... Ʒ j;

Cream................................................... f ℥ ss.;

Hot water................................................ f ℥ ijss.

This milk, when diluted, speedily undergoes lactic-acid fermentation and causes diarrhoea and thrush.

Condensed milk has been used with advantage in the treatment of dysentery (Hübner) and as a prophylactic against scurvy. It is serviceable on long voyages and expeditions where fresh milk cannot be obtained for use with tea, coffee, etc.

Unsweetened condensed milk made of fresh Swiss Alpine milk, and sold under various brands in this country, is prepared by evaporation by heat sufficiently strong to render the milk aseptic, so that no preservative materials are added. The water is reduced from the normal standard of 88 per cent to about 61 per cent. It is open to the same objections as the use of sterilised milk (see Sterilised Milk, p. 85), but it is better for infants than those forms of condensed milk in which preservation is secured by the addition of too large a proportion of cane sugar. An analysis of one brand of this milk is given by Professor Goodfellow, as follows:

Water

61.3

Casein

9.1

Albumin

1.5

Fat

11.7

Lactose

14.3

Salts (mineral matter)

2.1

100.0

Milk may be preserved for some time in hermetically sealed cans or bottles without previous condensation, but a separation of the cream eventually takes place, and butter forms in the can.