gingebee is of course correct as is Old Geezer - we regularly freeze left over milk when we go away and it is fine thawed on return. Semi-skimmed is probably a bit better than full-fat. On the other hand, milk and cream in the UK do not go sour when they go off, they go horribly bitter and utterly unusable. I have asked the UK milk marketers but received no reply. I asked abroad where milk and cream still go sour and they are not entirely certain what could be the reason but said that if it is not by addition of preservatives then it is possibly due to different processing methods (pasteurisation) or even milking methods (automatic equipment).