HORRIBLE taste expressed breastmilk frozen&refrigerated

what the heck am i doing wrong?

i express milk and freeze it. when there's room in the container, i refrigerate new milk and add it to the frozen milk only if the frozen milk is more than the new milk.

TWO times now, i've defrosted milk and in under 24 hours, it tastes HORRIBLE and has a metalic smell. i've wasted 8 ounces already because of it.

what am i doing wrong? i'd NEVER feed it to my baby if it tastes like that  

Sounds kind of like a lipase issue and nothing you are doing wrong yourself.

Have you tried putting your milk in ice cube trays and freezing them individually? Then you can store them, but make sure you date the container/bag so you use older milk first?