If there's a lipase issue, there's not much you can do about the already frozen milk, but if you think that's the case, you might want to scald the milk that you're freezing going forward. Here's the kellymom link for lipase: http://kellymom.com/bf/pumpingmoms/m...expressedmilk/. But I wouldn't make the assumption that there is a lipase issue because your son doesn't drink a whole 5 ounce bottle - that's a lot. 2-3 ounces is more like what most babies typically drink from the breast. Does the milk smell/taste soapy?