Why is salt added to the ice water bath when you are making homemade ice cream?

Salt lowers the freezing point of water.





Salt added to crushed ice creates a slush that will stay liquid at temperatures well below the freezing point of water.





Water freezes at zero Celsius, but a saltwater solution won't freeze until it gets around -10C or so.Why is salt added to the ice water bath when you are making homemade ice cream?
NaCl for affectionately known as salt actually lowers the temperature of the ice! Ice is at 32掳F in it's solid state.





When heat is added to ice the ice turns to water, but stays at 32掳F until it's no longer ice.





When salt is added to ice it melts so rapidly that it uses some of it's own thermal energy to turn itself into water. When the ice gives up it's thermal energy it becomes colder and the ice and salt water mix can be as cold as 14掳 - 15掳 F.


The cream mixture inside the canister is warmer than the salt water ice mix, so it gives off it's heat to try to stabilize the temperatures between the two mixes, inside and outside of the canister, causing the ice to melt more and the homemade ice cream to freeze more.Why is salt added to the ice water bath when you are making homemade ice cream?
Since the ice starts at a temperature well below the freezing point of water and the ice cream needs to be below the freezing point of water to set up something has to be done to keep the water as a liquid even when it is very cold -- i.e., below its normal freezing point. Dissolving salt in the water serves this purpose. It lowers the freezing point of the water so that it can be very cold and remain a liquid, providing good thermal contact with both the ice and the ice cream container. In fact, you do not add water to the ice cream maker, you add ice and salt. The salt slowly is dissolved in the melting ice water, lowering its freezing point so that the water can drop in temperature to the ice temperature without freezing. The same thing happens when you put salt on a sidewalk covered with ice. The surface of the ice has a thin layer of water which begins to dissolve the salt. The salt later has a lower freezing point and stays liquid at very low temperatures.
Well, salt actually contributes to the taste of the final ice cream
To expand on the previous answer, you need a temperature well below 0掳C to make good ice cream.聽 The sugars and stuff in the cream depress the freezing point and you need to freeze it relatively quickly to keep the ice crystals small, otherwise the ice cream will be grainy rather than smooth.聽 (This is why liquid nitrogen works so well for making ice cream; it is REALLY cold!)





Ice without any help just sits there melting at 0掳C and won't freeze cream at all.聽 Adding a lot of salt forms a brine, which allows the ice to melt at closer to -15掳C.聽 This is cold enough to freeze the water in cream relatively quickly and give you good ice cream.