It is because the liquid in the bottle is supercooled – the temperature of the liquid is below its normal freezing point, but the liquid has still not turned into a solid. That’s because it needs something to kick-start the freezing process and encourage a small number of the liquid molecules to get together in a regular arrangement, as they do in a crystal, instead of moving around independently as they do in the liquid.
Process of Turning Water into Ice
The process is called nucleation, because it encourages the molecules in the liquid to form a crystal-like nucleus onto which others can then latch. The kick-start can be given by a piece of dust, a rough spot on the surface of a container, or the shock wave generated when you hit a bottle just out of the freezer. Shock waves from an in-built metallic ‘clicker’ are used in a new ‘wine warmer’ which contains a supercooled liquid that releases heat as it solidifies.