How long is the protein in a protein shake good after it is mixed?

I have heard that once you mix protein with water, juice, etc. that you have to drink it within a certain amount of time or the protein will disintergrate or something. Is this true? And if so, how fast do I have to drink the protein?

We greatly appreciate your interest in helping us build our Q&A database. To discourage vandals from posting garbage, however, we require people to register before posting.