Why has my breastmilk started to smell sour?
A few mothers find that their refrigerated or frozen milk begins to smell or taste soapy, sour, or even rancid soon after it’s stored, even though all storage guidelines have been followed closely. Per Lawrence & Lawrence (p. 781), the speculation is that these mothers have an excess of the enzyme lipase in their milk, which begins to break down the milk fat soon after the milk is expressed. Most babies do not mind a mild change in taste, and the milk is not harmful, but the stronger the taste the more likely that baby will reject it.
