Why Add Rock Salt to Ice for Ice Cream?

If an ice cream maker requires ice, add salt to it

Without rock salt to lower the freezing point of the ice, it would not be possible to make ice cream in a hand-cranked or traditional electric ice cream maker. Ice naturally melts at 32 degrees Fahrenheit, which is too warm to create ice cream.

Process

According to sendicecream.com, rock salt forces the ice surrounding the can of ice cream to melt, creating a brine solution that lowers the ice cream's temperature to help it freeze.

Temperature

Without adding rock salt, the ice would melt at 32 degrees Fahrenheit. The ice cream must be at least 27 degrees Fahrenheit in order to freeze. The ice lowers the melting point of the ice to between eight and 12 degrees Fahrenheit.

Ratio

According to sendicecream.com, you need one cup of rock salt for every five cups of ice in your ice cream maker.

Table Salt

Some scientists who participated in the the "Ask a Scientist" column at newton.dep.anl.gov believe table salt can be used instead of rock salt to make ice cream. One scientist, however, suggested that table salt may lower the brine temperature too quickly, causing ice crystals to form in the ice cream.

No Salt

If an ice cream maker requires ice, you must use salt. If the ice cream maker does not use ice, it lowers the temperature of the ice cream automatically without a salt brine.

References

• Sendicecream.com: How does the rock salt work?
• Newton.dep.anl.gov: Ask a Scientist -- Table vs Rock Salt for Ice Cream