If so, it might be excess lipase. The only way to fix it is to scald milk after pumping which wouldn't do you much good since I think you said you are done pumping.
My DS wouldn't take my frozen BM either when I went back to work at 6 mo. We ended up mixing the frozen and fresh together in a 1:1 ratio and he took it like that with no problem until just after 1 yr. If you are going to move to formula, can you just start formula now and mix it with the formula? I think you could call an LC to determine the right amount of BM to mix. I never used formula but I thought I saw that someone on here was doing that(months ago).
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Re: Hates frozen BM
Does it smell metallic or taste soapy?
If so, it might be excess lipase. The only way to fix it is to scald milk after pumping which wouldn't do you much good since I think you said you are done pumping.
But maybe it is something else...?