milk

[Bugsbabs]

what is the reason for cow's milk turning yellow when frozen?

[New Forester]

Milk is an emulsion.  This is a mixture of two separate types of liquid, usually an oily one and a watery one, one very finely divided and floating in the other.  Milk and cream are very tiny blobs of butter-fat floating in butter-milk (even skimmed milk still has some very tiny blobs).  Butter is reversed -- it's an emulsion of butter-milk in butter-fat.  Mayonaise is an emulsion of salad oil in egg.

 

The white effect in liquid milk is caused by each of the little round blobs scattering the light, much as the air in snow does.  As this does not happen when milk's frozen, I think the blobs must be squeezed between the ice crystals, revealing their true colour -- butter-yellow.