I have started pumping and freezing or refrigerating some milk in an attempt to get DS (11wks) used to taking a bottle sometimes as I plan on returning to part time work in a few months. The first time we tried him with 1day old milk that had been stored in the fridge, warmed slightly under room temp/lukewarm water, and after a short battle, he drank it.
Now we tried him on about 2week old frozen milk, defrosted and warmed slightly under room temp/lukewarm water and after a battle he started to suck and spit it out. Then I noticed it was kind of 'bitty' like tiny dots getting stuck all around the bottle. I didn't notice it with the refrigerated milk, only the frozen. I decided not to keep trying in case I had spoiled it somehow? Did I do something wrong with the frozen milk?

TIA