MILK AND ITS PRODUCTS. 
It has to be borne in mind that sweetened condensed milk is not 
sterile, but that bacterial growth is kept in check by the high per cent. 
of sugar and the lack of moisture in the highly concentrated medium. 
It is rather a too-common occurrence to open a tin in which bacterial 
growth has injuriously affected the contents. In the concentrated milks 
it has been found necessary to add boric acid as a preservative in our 
warm climate. The unsweetened milk, however, is sterile. To make 
it so it has to be raised to a much higher temperature. 
In making sweetened condensed. milk, fresh milk, partly or wholly 
skimmed, is heated to near boiling, and 16 lbs. of sugar are added for 
each 100 Ibs. of milk, and the mixture condensed in vacuo at 130-150° F. 
until the ratio of 24:1 is reached (7.e., 24 volumes of fresh milk are 
S.W. ms : 
SCHEME TO ILLUSTRATE THE SPRAY METHOD OF DRYING MILK. (After Delépine. 
S.W. Automatic Weigher and Strainer. M.V. Mixing Vat. H. Heater. §. Separator. 
C. Cream, removed if drying skim milk, otherwise may not separate. P. Pasteurizer. S.H. Steam- 
heated concentrating pan. V.P. Vacuum Pan. From V.P milk drawn into metal cylinders (2nd 
row C), from which it is pumped to P.T., Pressure Tank, then by P., Force Pump, along with A., . 
Hot Air, into Tin-lined Tank or Evaporation Chamber, E.C. Vapour removed’ at A.O. or may go 
through 2nd chamber. P.M. Milk Powder removed from floor-trap, and sifted through fine gauze 
sereen, G.S. N. Nozzle. 
condensed to 1 vol.). The finished product contains 40 per cent. sugar, 
and its specific gravity is 1-29. It is not sterile. 
If whole milk is to be condensed, it is more usual to separate the 
cream and add it later to the condensed skim milk. The cream should 
be pasteurized. Condensed and powdered whole milks tend to become 
rancid, and there is also some change in the physical condition on 
standing. The fat may be prevented from rising by homogenizing the 
milk. 
-In the preparation of condensed milks, the temperatures must be 
kept as low as possible, to prevent charring of the sugar and so 
darkening the colour of the finished milk. Hence the use of concen- 
tration in vacuo, This means the use of special machinery, thus adding 
to the cost of the finished product. 
In the preparation of dried milk powders there are many systems 
in use, such as the Ekenberg, the Just (-= Miatmaker in Europe), the 
Campbell, the Passburg, the Merrell-Soule (original Stauf patent in 
Germany in 1901), the Dick, and the Grey-Jensen. Most of these 
219 
