NEUTRALIZATION OF SOUR CREAM 165 



Magnesium limes, which contain 35 to 50 per cent MgO 



have an alkalinity equal to 115 to 120 per cent of pure cal- 

 cium hydrate. Their use requires only 2 pounds of the lime 

 in one gallon of mix, to reduce the acidity to .25 per cent by 

 the use of the neutralizing tables, appended. This lime mix is 

 lighter and thinner, more easily agitated and made uniform in 

 strength when used. The magnesium lime is perfectly whitte 

 and very finely pulverized, it distributes more readily in the 

 cream and acts very satisfactorily. It does not convey to the 

 cream any objectionable flavor. Lime stone, as a rule, con- 

 tains either a large percentage of magnesium (35 to 50 per cent) 

 or a very small percentage of magnesium, less than 5 per 

 cent, though there are exceptions. If magnesium lime is pur- 

 chased, therefore, with the intention of securing a, lime with 

 relatively high neutralizing power, it should be ascertained 

 that the lime contains 35 or more per cent of magnesium. 



Analyses 1 show that the hydrated limes containing mag- 

 nesium contain only enough water to satisfy the calcium. These 

 limes, therefore, are a mixture of calcium t hydrate and mag- 

 nesium oxide. 



Incomplete Reaction of Lime in Cream Due to Affinity of 

 Lime for Curd. In previous paragraphs it was shown that 

 while the lime is capable of, and does exert its full neutralizing 

 strength in aqueous solutions of lactic acid, a portion of the 

 lime, about 16 to 20 per cent, when added to sour cream, 

 fails to so act. It remains now to explain why all of the lime 

 does not react in the cream and what becomes of that portion 

 which fails to react with the acid in the cream. 



It is well known that the casein has a marked affinity 

 for calcium. In raw, sweet milk and cream the casein is 

 present as a calcium salt. When cream becomes sour, the lac- 

 tic acid thus formed removes calcium from the casein. This 

 leaves a part of the casein as free casein which is a solid, and 

 a part occurs as casein lactate which is in a colloidal state. 

 The casein lactate, however, is readily hydrolized; upon neu- 

 tralization it is precipitated, becoming solid, so that from the 



1 Brigham, S. T. Engineering news, Vol. 50. 



