I warmed up some milk earlier today that was pumped 5 days ago (1-9-12) to mix with DD's oatmeal. I tested the oatmeal to make sure it wasn't too hot & it tasted off. DH agreed so I tried a tiny taste of the milk that was left in the bag & it was definitely sour. Wouldn't say soapy necessarily, but it was gross - definitely sour. I almost threw up. I've read about lipase but have never had trouble with this before & I've reheated milk that is up to a week old (refrigerated). DD always takes her bottles willingly. So my question is - can lipase just develop randomly or is it something I would have had all along? I have been building quite a stash in my fridge/freezer so it would totally be a bummer if it was all bad. Or maybe it was just that one bag that went bad for some reason? Usually when I pump at work I let the bottle sit til the next session (to avoid adding warm to cold) if it isn't full, so maybe it went bad then? It's only 3 hrs at most. I'm kinda freaking out here - not sure I can deal w/scalding all my milk!