How do I know if my expressed milk is bad already?

Determining if breast milk has gone bad, "If breast milk has been stored longer than the guidelines recommend, it should be thrown out. Remember that all breast milk is not going to look the same, as it varies in color. If fat in the breast milk separates during storage, shake the container and the fat will mix with the milk. Breast milk can sometimes taste or smell soapy; fat can also break down during storage, causing this smell. Note that it is still safe to consume when this happens. Spoiled milk will smell sour and should not be consumed." From: http://www.livestrong.com/article/507375-how-do-i-know-if-my-stored-breast-milk-is-bad/