Sodium chloride is commonly mixed with ice to create the freezing bath used in traditional ice-cream making.
Adding salt to ice lowers the mixture’s melting point. As the ice melts, the saltwater brine can become colder than ordinary ice alone, allowing it to draw heat from an ice-cream mixture inside a surrounding canister. The mixture freezes while being stirred or churned.
This technique was central to hand-cranked ice-cream freezers before electric refrigeration became widespread. The salt does not normally become an ingredient in the finished ice cream; it remains in the external cooling bath, separated from the food by the freezer container.
People sometimes call this process “freezing with salt,” but the salt is not freezing the ice cream directly. It creates a colder environment that transfers heat away from the cream mixture.