TO STERILIZE MILK FOR IMMEDIATE USE.—­Put the milk as soon as received into the inner dish of a double boiler, the outer vessel of which should be filled with boiling water.  Cover and heat the milk rapidly to as near the boiling point as possible.  Allow it to remain with the water in the outer boiler actively boiling for half an hour, then remove from the stove and cool very quickly.  This may be accomplished by pouring into shallow dishes, and placing these in cold water, changing the water as frequently as it becomes warm, or by using pieces of ice in the water.  It is especially important to remember that the temperature of the milk should be raised as rapidly as possible, and when the milk is sufficiently cooked, cooled very quickly.  Either very slow heating or slow cooling may prove disastrous, even when every other precaution is taken.

Or, well-cleaned glass fruit cans may be nearly filled with milk, the covers screwed on loosely, then placed in a kettle of cold water, gradually heated to boiling and kept at that temperature for a half hour or longer, then gradually cooled.  Or, perfectly clean bottles may be filled with milk to within two inches of the top, the neck tightly closed with a wad of cotton, and the bottles placed in a steam cooker, the water in which should be cold at the start, and steamed for half an hour.

This cooking of milk, while it destroys many of the germs contained in milk, particularly the active disease-germs which are liable to be found in it, thus rendering it more wholesome, and improving its keeping qualities somewhat, does not so completely sterilize the milk that it will not undergo fermentative changes.  Under varying conditions some thirty or forty different species of germs are to be found in milk, some of which require to be subjected to a temperature above that of boiling water, in order to destroy them.  The keeping quality of the milk may be increased by reboiling it on three successive days for a half hour or longer, and carefully sealing after each boiling.

TO STERILIZE MILK TO KEEP.—­This is a somewhat more difficult operation, but it may be done by boiling milk sealed in very strong bottles in a saturated solution of salt.  The milk used should be perfectly fresh.  It is best, when possible, to draw the milk from the cow directly into the bottles.  Fill the bottles to within two inches of the top, cork them immediately and wire the corks down firmly and place them in the cold salt solution.  Boil fifteen minutes or half an hour.  Allow the solution to cool before removing them.  If the bottles are removed from the solution while hot, they will almost instantly break.  When cold, remove the bottles, and cover the tops with sealing wax.  Store in a cool place, shake thoroughly once or twice a week.  Milk sterilized in this manner will keep indefinitely.

CONDENSED MILK.—­Condensed milk is made by evaporating milk in a vacuum to one fifth its original volume; it is then canned like any other food by sealing at boiling temperature in air-tight cans.  When used, it should be diluted with five times its bulk of warm water.