Scalding milk is the recommended solution for excessive lipase. The breastmilk is still chock full of immunities and nutrients for your baby, scalding is the safest way to reduce the lipase, which as you can see is making the milk taste unpleasant. Lipase is the enzyme that breaks down fat in the milk.
Per the Breastfeeding Answer Book, page 229, "If the mother finds after freezeing and thawing that her milk has a rancid smell, she can prevent this from occurring in the future by heating her expressed milk to a scald (bubbling around the edges but not boiling) right after collecting it, and then quickly cooling and freezing it. Scalding inactivates the lipase (Lawrence and Lawrence p. 696). Once the milk has acquired the rancid smell, however, treating the milk will not help. It is not known whether or not this milk is safe for the baby; however most babies refuse it.
Some mothers have reported a slightly soapy smell to their frozen milk after it was thawed. This change in smell has been attributed to changes in the milk fats related to storage in self-defrosting refrigerators-freezers; it has not been found to be harmful to the baby (Lawrence and Lawrence, p.696)."
These above guidelines are assuming baby is healthy and full-term, if you have a premature baby the guidelines may be different,
check with your baby's doctor.