why does my white sauce sometimes go watery/curdle when I make fish pie?

[hatwoman]

it happens to dh more than me, but last time I did a fish pie it happened to me. I was gutted. does anyone know why it happens?

Do you cook the fish before adding the white sauce? I get much better results if I poach the fish until it is just cooked, drain it on kitchen paper to absorb most of the moisture, then put in the dish and pour the white sauce over (if your sauce is thick enough to start with, you can add some of the fish cooking water to the sauce for extra flavour).

usually I poach the fish in milk and use that milk for the sauce. I haven't drained the excess moisture though - so perhaps thats something to try

are you using fish that has been frozen?

You could try adding some cornflour to your sauce.

I forget exactly, but it's to do with temperature. Do you make the white sauce first then put in pie and bake for a bit? I can't remember exactly but I think it curdles if you put cold liquid into the hot sauce? So if you've been faffing around and then mix it all up again? Someone more scientific than me can probably give an exact answer. But for example, pouring cold wine into an already made white sauce is always a disaster.