It's a white circular plastic seal that sits in the cap stopping any leakages.It's part of the cap,but this time when I removed the cap it stayed on the bottle,when I poured it in I noticed it,but it was too late by then.
When I got home I opened another bottle,the white plastic seal was inside the cap,but with a small wiggle with my fingers I managed to remove it.It's like opening a screw top milk carton,u unscrew the cap,then have to remove the white strip.Same thing ,but on the millers the white bit sits in the cap and isn't attached to the bottle..........if that makes any sense.