Today’s invention is the latest weapon in the communal-fridge wars.
To stop people stealing one’s (personal) milk, insert a plastic device which consists of a number of yellowish globules linked by a few strands of fishing line. The globules float near the surface and the lines are almost invisible.
This gives the impression, when viewed through the bottle wall or neck, of milk substantially past its use-by and thus deters all but the most desperate kleptolactics.
This device is sterilisable between uses and easily placed in a bottle but won’t pour into one’s cup every time the milk is used.