Once mothers start expressing their milk, they need to know what the perimeters are as far as storage is concerned. And this is confusing because so many books and websites and advice from other people are really conflicting in that. The advice that I've been telling moms for a long time and it seems to work in general is the rule of fives. SO if you first express your breast milk, you can actually leave it out unrefrigerated for five hours. If you're not going to use it in five hours, it should go in the refrigerator and it's good for five days. If you're not going to use it in five days, you can put it in the freezer for five months. And then defrosted milk is good for about 24 hours. Having said that, I would never throw milk out unless I knew it was actually sour. So mom's say, "Well how do I know that?" Well, human milk is the same as cow milk; it smells the same, tastes the same if it's sour. Also babies, if the milk is bad, they won't take it. So we have moms, for example, that have milk in a deep freeze for a year and it's still fine. So kind of use the rule of fives in general and then if you have milk that you really don't want to part with, I would make sure to see if it's sour before I threw it out.