Re: How does the process of souring in milk affect its calcium?

This was referred to me as a microbiology question, which it is not.  
Although souring of milk is caused by bacteria, the lactic acid could as 
well have been added to the milk from some other source.  In any case, 
calcium as lactate appears to be as nutritious as calcium in other forms -- 
calcium lactate is listed as one of the most biologically available forms 
of calcium.

I have not found anything to suggest, in the way of specific methods of 
analysis.  In the U.S., the most respected reference to this kind of 
information is:  Official Methods of Analysis of the AOAC (Association of 
Official Analytical Chemists) International, 16th ed., Arlington, VA, 1995. 
 If you can find a copy, it should offer more than one method that is 
current.