The Age Thickening of Sweetened Condensed Milk III. Effect of Reaction and Changes in the Electrical Conductivity during Manufacture and Aging

In a sensitive colloidal system such as milk small changes in the .various ionic concentrations are likely to exert a great influence on the stability of the system. Since the electrical conductivity of milk depends upon the various ions present and the hindering effect of the non-electrolytes, it is reasonable to expect that any changes occurring in the ionic equilibrium and the concentration of the non-electrolytes during the manufacture and aging of sweetened condensed milk would be reflected in a change in the electrical conductivity. It is a matter of common experience that an increase in .acidity almost invariably decreases the heat stability of milk. With these facts in mind, electrical condaetivity and hydrogen-ion concentration measurements were made during the preparation and aging of several batches of sweetened condensed milk. The different batches varied in their stability toward age thickening. E X P E R I M E N T A L i//IETHODS The pII measurements in these trials were made at 25 C. (77 F.) with the quinhydrone electrode and a saturated calomel half-cell. FIG. l. SPECIAL ELECTI%0DE USED IN i%/[EASURING THE ELECTRICAL CONDUCTIVITY OF Conductivity measurements were made according to the Kohlrausch method using a Leeds and Northrup microphone hummer, a Leeds and Northrup precision Wheatstone bridge and tunable telephone receivers. A special type of electrode was used so that it could be inserted into the tube of condensed milk when making a measurement without it being necessary * Pub]