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Add salt to the ice bath in an ice cream maker.

We know that water turns to the ice (solid) phase at $0°C$, but the temperature of the ice bath must be less than $0°C$, which can be accomplished by adding salt to the ice bath system. Adding salt to the ice bath system lowers the phase temperature, resulting in a lower transition temperature between the phases. The kinetic energy of the particles in the mixture determines the temperature of the mixture, and as the kinetic energy reduces, the temperature of the mixture decreases.

The ice cream and salt mixture are insulated from the environment in the ice cream making system, which means that the energy required to break the chemical bonds of the salt crystal must be taken from the kinetic energy of the mixture particle, resulting in a decrease in kinetic energy and thus the temperature. As a result, the ice cream bath is always below 0 degrees Celsius.