Pardee, I have had a mom have a similar experience with milk spoilage - she used the Playtex nurser bags. I have not had anyone complain of spoilage with the Ameda/Egnell milk bags, because they are nylon lined and very thick; but then again I only recommend them for premies or ill babies that need every last molecule of fat. One suggestion for self-defrosting freezers is that the mom store the bags of milk in a bowl of ice to prevent the milk from warming and spoiling during the defrost cycle. My moms have found this useful. Catherine Watson Genna, IBCLC