Frozen thawed milk tastes different from fresh. How do I know? Because I was basically dared by my mother-in-law (MIL) to try my own breast milk (yes…). At the time, my baby was about 3 months of age and wasn’t taking breast milk well from the bottle. My MIL suggested it was the taste of the thawed breast milk, as her friend said her grandchildren had the same issue because the thawed breast milk did not taste good. I knew breast milk usually tasted slightly sweet because of the lactose content, but I didn’t really believe my MIL that there could be such a vast difference in taste between fresh and frozen to affect baby’s intake. Especially since I had learned as a dietitian that a baby doesn’t usually develop a strong taste preference until after 6 months of age. Before then it was often possible to get a baby established onto a more bitter tasting hydrolyzed formula even if the baby had been used to the sweet taste of breast milk. And after all, if the expressed breast milk had been quickly frozen, wouldn’t that slow down the lipase enzymatic action on the fats within the breast milk and so prevent the breast milk from going ‘off’ in taste? Well, my MIL then implied that if I didn’t believe her I should taste the breast milk myself. So I did. In front of her.
And okay… there IS a difference. Fresh breast milk tastes…fresh…a bit like cow’s milk but lighter, more watery and with a slightly sweet taste. The thawed breast milk tasted more bitter and metallic. I found it had to be heated more in temperature to make it more palatable tasting.
My little one still took the thawed frozen breast milk (sometimes with a bit of cajoling and distraction with a toy) from a bottle until about 4-5 months of age, then after that she seemed to get wise to the fact that it really didn’t taste very good, and so refused more adamantly to take it (even when she was really hungry). She would always drink fresh pumped breast milk though!
What I have found I needed to do was this: Give the frozen breast milk as soon as it has thawed. This means really within the first hour or two after it has been thawed out in the fridge. Doing so will keep the thawed frozen breast milk tasting as close as possible to freshly pumped milk. Any more than that, and the bitter, metallic and soapy taste starts to appear, especially the longer it sits (mainly because of the active components within the breast milk like the lipases which start to break down the fat within the milk).
Note that even if there are some taste changes in the thawed breast milk, you can still use it in the baby’s food, assuming the baby is eating at least a few tablespoons’ worth of solids in a sitting. This gets easier to do as baby gets bigger and eats more at a time. So don’t toss all your hard work of pumping away!