228 CONDENSED MILK. 



in two of water. Evidently, then, properly prepared condensed 

 milk contains milk sugar in super-saturated solution; any favour- 

 ing condition will precipitate the lactose as gritty crystals. 



The chief factor which makes permanent super-saturation 

 possible is the high viscosity of condensed milk due to casein and 

 cane sugar. Small portions oi undissolved sucrose in the original 

 solution, overheating, too rapid cooling, or even excessive stirring, 

 may lead to grittiness. 



Another important defect is "settling." This means separa- 

 tion of cane sugar. It is almost impossible to get a condensed milk 

 containing no sugar crystals. With proper attention to details, 

 however, these do not separate out, and it will be apparent that 

 viscosity plays a big part in the defect. If about 2-5 parts of 

 fresh milk have produced 1 of condensed milk, the density is 

 usually correct. Higher or lower density favours settling. 



For the same reason fat content is important, and of cour c e 

 the proper proportion of !-ugar must be adhered to. 



Lumpy, buttony, rancid, and cheesy milks may all be pro- 

 duced from good milk and sugar if scientific control is lacking. 



Every properly equipped factory has a laboratory. In this 

 both raw materials and finished product are tested, and defects 

 ■ever likely to crop up are investigated. Batches of fresh milk are 

 examined for total solids, fat and aciditv. Milk excessive in fat 

 is separated; the milk of high acidity is rejected. The reductase 

 test for micro-organisms is generally sufficient, but occasional 

 controls for tubercle bacillus should be made. The total solids 

 give a simple control over the output of the factory. 



For the analysis of the finished product, 40 grammes of milk 

 are dissolved in water and made up to 100 c.c. 5 grammes are 

 weighed into a platinum dish containing ignited asbestos, and 

 total solids and ash determined. The protein matter is determined 

 by multiplying nitrogen estimated by Kjeldahl by 6-38, or pre- 

 cipitation by copper sulphate may be employed. 



For fat II c.c. of the solution are precipitated with 5 c.c. of 

 copper sulphate. Precipitated casein and fat are separated from 

 the sugar solution by means of the centrifuge. After thorough 

 washing these are decomposed by the addition of 13-75 c.c. sul- 

 phuric acid and 1-25 c.c. amyl alcohol. After further centrifuging 

 the Leffmann-Beam bottles in which these operations are carried 

 out are heated to 66° C, and the fat in the neck of the bottle 

 read off. The number of the graduations multiplied by 04 gives 

 the percentage of fat. 



For sugars, 25 c.c. of the milk solution are placed in a large 

 test tube with 19-5 c.c. of water and 1 c.c. of mercuric nitrate. 

 After centrifuging the sugar solution is filtered off and read direct 

 in a 2-2 decimetre tube. 20 c.c. are then inverted by boiling for 

 ten minutes, and then are made up to 25 c.c. The reading of 

 this inverted solution multiplied by 5/4 gives B in the formula. 

 The direct reading by the polariscope is A of the formula. The 

 formula is: — 



