Effect of Certain Salts on the Stability of Skimmilk as Determined by Rennet Coagulation Time and Alcohol Test

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Abstract
Addition of Ca ions to skimmilk greatly decreased stability as measured by rennet coagulation time and alcohol test. As little as 1 mg Ca ion/100 ml of milk distinctly lowered rennet coagulation time. Measurement of soluble and ionic Ca before and after addition of Ca ions indicated that only about 1/4 of the added Ca remained in the ionic form. Adding up to 60 mg/100 ml of Ca ions shifted the ratio of soluble to ionic Ca from 0.33-0.42 and the ratio of ionic to soluble Ca from 0.56-0.64. Addition of citrate increased rennet coagulation time and alcohol test value, whereas phosphate did not have a similar stabilizing effect. Addition of citrate counteracted the effect of added Ca, presumably by forming complex (CaCitr)- ions. Phosphat apparently cannot form complex ions with Ca. Measurement of the rennet coagulation time was sensitive and reproducible for measuring milk stability. It gave results similar to the alcohol test but had definite advantages.