What are the guidelines for this? When I only get two ounces in one pumping session, I want to combine the freshly expressed milk with two ounces of milk that had previously been expressed, making a four ounce bottle. Typically, they're already in the fridge or freezer. What do I need to do when the ebm is already cold in the fridge? What about when it's already frozen? Can I put them in the same container or do they have to remain separate until they're warmed and consumed?