227 



CONDENSED MILK IN SOUTH AFRICA FROM THE 

 CHEMIST'S POINT OF VIEW. 



BY 



A. A. Kloot, B.Sc, F.I.C., and Leslie Hyman. 



Read July 13, 1921. 



Sweetened condensed milk, or just condensed milk, is the whole 

 milk of the cow evaporated to a more or less definite consistency 

 and sweetened with cane-sugar. The latter serves the double pur- 

 pose of sweetening and preserving. 



The aim of the manufacturer should be to produce an article 

 which, when diluted according to instructions, gives a whole milk 

 as produced by the cow plus the sugar added. This is not gener- 

 ally attainable as the finished article invariably has a flavour of 

 its own, due to the cooking process through which it has gone. 

 Apart from slight changes in the composition of the protein 

 matter, made up condensed milk is practically identical with 

 sweetened fresh milk. It has been demonstrated that the water 

 and fat soluble vitamine content is not affected by the process of 

 manufacture ; though it is probable that the anti-scorbutic vita- 

 mine is destroyed to some extent. 



A brief outline of the manufacturing process may now be 

 given. First a quantity of cane sugar solution is made with a 

 portion of the milk. Best refined sugar is advisable. The sugar 

 solution is then united with the main portion of the milk, and the 

 whole passed through a p re-heater into a vacuum pan. The latter 

 must be of copper on account of the action of weaker acids. A 

 vacuum is raised, and the milk is heated by means of a copper 

 steam coil in the. bottom of the pan. 



It is necessary to control the temperature very carefully, as 

 exceeding a temperature of 140° F. is likely to cause faults in the 

 milk. As the water evaporates from the milk fresh milk is auto- 

 matically sucked into the pan until the batch is complete. Tha 

 desired consistency is shown by a gravity of 1-28 — 1-30, but the 

 experienced worker knows instinctively when to "strike" a batch. 



The condensed milk is then run into cooling pans where it is 

 well stirred, then to a scale for weighing, and finally to the storage 

 tanks. From here the milk passes to an automatic tin-filler, and 

 sealing, labelling and packing complete the process. 



This description is necessarily short, but it should be remem- 

 bered that at least nine different defects caused by unscientific 

 management are possible, all or any of which are sufficient to 

 render the milk unmarketable. Most important is "grittiness." 

 This is most often due to precipitation of milk sugar. This is 

 readily distinguished from cane sugar under the microscope. 



Milk sugar at ordinary temperatures dissolves in six parts of 

 water. Condensed milk contains 12 to 15 per cent, of milk 

 sugar and 26-5 per cent, of water. This means one of milk sugar 



