I put milk into a bottle to see what would happen. It has been in there for about 3 months?!
Give it a little air. Then reseal it for another 3 months.
Since you refrigerated it, no bacteria had a chance to grow. You should have put it on the kitchen counter or something if you really had to do this experiment.
if you kept in in an airtight container the fridge it wouldn't work because the bacteria which make it solid need warmth and air to thrive,