This question already has an answer here:

We have a bottle of milk that is half gone. It is not sour.

If I pour hot water onto instant coffee, and then top up with this milk, the milk splits into a grainy solid.

If I repeat the process but use a newly opened bottle of milk, the milk does not split.

Why does the first lot of milk split?

Thanks in advance.


marked as duplicate by Mithoron, airhuff, andselisk, Jon Custer, Tyberius Jan 31 at 17:37

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • 1
    $\begingroup$ The milk is starting to sour, and will curdle in hot water (coffee, tea whatever) before it will noticeably curdle in the cold fridge. $\endgroup$ – MaxW Jan 31 at 2:25