The Society "Le Ferment" of Paris, which has been authorised by Professor Metchnikoff to prepare and supply to the public his sour milk culture, provides an apparatus for the treatment of the milk. It is shown in Fig. 45, which consists of a double box having the intervening space packed with a non-conducting material. It is provided with a tight lid. Inside, there is accommodation for two milk vessels, each with a capacity of about two thirds of a pint. The most difficult thing in the souring of milk is to maintain the temperature as nearly at 100° F. as possible while the culture is in action. This result is attained by filling the vessel in the middle with boiling water. The insulated walls hinder the escape of heat, and the quantity of boiling water used is calculated to maintain the temperature steady for the twelve hours of cultivation; but in cold, frosty weather it is necessary to refill the central vessel with boiling water in the middle of the period.
Fig. 45
The milk jars are washed with hot boiled water and turned upside down to dry. They should not be wiped with a cloth. Boil the milk to be treated for ten minutes, stirring it to promote evaporation, as it is advantageous to have it in concentrated form. Cool rapidly to 100° F. by placing the boiling vessel in cold water, add to each bowl one third of a tube of the culture in powder form, fill up with the boiled and cooled milk, stir well and cover. Place the jars in the box and fill the central vessel with boiling water, shut the lid tight, and do not open it (unless a fresh charge of boiling water is needed) for ten or twelve hours, when it will be ready for use. If the liquid culture is used (one small phial for each bowl) the milk should be cooled to 86° F. instead of 100° F., as with the powder. The culture is also supplied in tabloid form. The powder and tabloids keep well, but the liquid can only be relied on for about two months. The milk prepared as above should be stored in a cool place, the lids being kept on the bowls. It is good for about two days, after which it becomes too sour. It can be eaten with sugar, which not only sweetens it but is beneficial in affording additional suitable food for the acid-producing bacilli. If fresh milk cannot be had, condensed, sterilised, or pasteurised milk may be used, but, of course, fresh milk is best. Condensed milk should be diluted with two parts of boiling water and then treated like ordinary milk.
An apparatus on similar principles is sold by the Maya Bulgare Company, Ltd., and is illustrated in Fig. 46.
Fig. 46—Soured Milk Apparatus of the Maya Bulgare Company, Limited, consisting of an insulated box, hot-water vessel, and covered vessels containing the milk and culture. The apparatus consists of cabinet in deal, Maya Bulgare ferment in 20-dose bottles, Maya Bulgare ferment in 100-dose bottles, compressed Maya Bulgare tablets in boxes of 8 tubes, Maya Bulgare caramels in boxes of 40, reduced milk, china funnels, and thermometers.
The box is insulated, but the door is on the side, the hot water vessel is underneath, and the covered vessels containing the milk and culture are placed on a shelf above. In the front of the illustration are shown the various packages in which the liquid and powder cultures are put up. The procedure is exactly the same as with "Le Ferment" apparatus.