Air in the concentrate should be avoided by any means, as it upsets the whole concentrate pre-treatment and drying.

It is possible to measure the content of air in the concentrate by using the equipment as shown in Fig. 102. The apparatus is set under vacuum with the glass stopper and valve B, C and D closed, and A open. The system is filled up by NaCl solution by sucking it into the apparatus by a vacuum pump, leaving the 100 ml concentrate container empty and 1-2 ccm of air in the graduated glass tube on the "air side".

Fig. 102  Laboratory measuring equipment for "Air in Milk Concentrate"

The concentrate to be tested should now be filled into the 100 ml container, which is then closed. The amount of air (should be 1-2 ccm) in the "air container" is noted. Then the vacuum pump is started again, and the valve A is opened slowly. By a proportional calculation of the expansion (shown in ml in the graduated glass pipes) of the "known" amount of air in the "air" container compared to the expansion of the un-known amount of air in the concentrate, it is possible to calculate the content of ml of air/100 ml of concentrate. Reference is made to Niro Analysis No. B 4 a.

Measurement of Insolubility Index is usually performed on milk powder, see page 203. Should it for example not be possible to trace the problems with too high insolubility Index by changing the drying parameters, it is recommended to perform the test on the concentrate. The amount of concentrate to be used is calculated as follows:

g concentrate  =   g powder x 100 / %TS of concentrate

g powder = 10 g skim milk, 13 g whole milk, or 6 g whey powder. The rest of the procedure is as described for powder.