Two months ago, I made a fish sauce (roux + milk + fish stock + lemon juice + cheese + mushrooms). I made way too much, so I decided to put a good amount (0.5 l / about 2 cups) in the freezer.
I wanted to use it this week, so I got it out of the freezer, and I put it in a sauce pan on a low heat, when it was still frozen. However, the result after it was fully heated, was not so good: it contained lumps (but not roux-lumps) so not at all the desired consistency.
Why/how did the lumps got there? Was it because I didn't properly defrost the sauce? Or was it a consequence of the freezing itself? What can I do to avoid this the next time?
There were no lumps when I made it.