306 THE SPRAY PROCESS 



must be attributed to chemical changes, one of the chief of which 

 is oxidation. While there are numerous agents, which come in 

 contact with, or enter into, the composition of milk powder, that 

 may bring about, or may invite oxidation, air is one of the most 

 likely factors to play an important role. 



Air, as is well known, acts as an oxidizing agent. Since 

 there is a noticeable tendency of the product from uncondensed 

 milk to be flakier and bulkier than the product from condensed 

 milk, it appears that with this increased bulkiness, there may 

 be more air in a given bulk, varying somewhat with the method 

 of packing. 



But experience has shown that there is enough air contained 

 both, in a package of milk powder made from uncondensed milk 

 and in a like package of milk powder made from condensed 

 milk, to cause deterioration, when other conditions, such as 

 light, or temperature, or both, are favorable, or when there is 

 present in the product enough moisture. 



There are no experimental results available that show any 

 difference in the keeping quality of the two products and the 

 experience of the commercial manufacturer points to the con- 

 clusion that the milk powder made from uncondensed milk 

 keeps as well as the product made from pre-condensed milk. 



Effect of Pre-condensing on Solubility of the Spray Milk 

 Powder. The flaky and fluffy powder of the uncondensed milk 

 goes into solution at the start somewhat slower than the more 

 granular powder made of condensed milk. This is due to the 

 fact that the flaky particles with their relatively large exposed 

 surfaces, coming in immediate contact with the water, dissolve 

 and take up water so rapidly, that they run together and paste, 

 forming a coating around the remaining mass of the product, 

 which renders the penetration of the water into the mass some- 

 what slower at the start. However, this is no indication that 

 the flaky powder is less soluble than the granular powder, in 

 fact the flaky powder, because of the large relative surfaces of 

 its particles and, therefore, the greater area of contact, does 

 dissolve more rapidly when it actually comes in contact with 

 water. 



Experiments conducted by Hunziker indicate that the differ- 

 ence in speed of solution between the two products is very slight 



