If you do have this problem apparently scorching the milk before storing it makes it keep longer, but that seemed like such a faff I never tried it, just gave up expressing (which I hated anyway, so was glad of the excuse!)
I think it's normal for the fattier milk to float to the top, you can just shake to mix it back in. Give it a taste if you're worried - it should keep in the fridge, but some people have too much lipase which makes it taste horrible pretty quickly. Mine only kept for a few hours.
I have been bf my 5 week old, and thought I'd try expressing. Having (slowly, painstakingly) expressed throughout the day, into sterile bottle which I kept in the fridge, I was a little (very) gutted to find that the milk looked curdled when I went to give it to DD. Down the sink it went .
Today the same has happened again, SO...can this be normal? Does ebm separate in the fridge? Is it safe to give? Help!