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Ice cream salt is a type of salt (sodium choloride) that is used to make homemade ice cream. It is not mixed in with other ingredients but is instead used to help make the ice that freezes those ingredients colder. If salt is not added to the ice, the ice cannot reach a cold enough temperature to freeze the ice cream. This salt is added to the outer containers of ice cream makers, and the interior chambers are filled with the ingredients.
Large salt crystals usually make up the majority of ice cream salt, which is sometimes referred to as rock salt. It can also be used to melt ice on roads and sidewalks. Although the cook may need to use more of it, table salt can sometimes be used as a substitute, if needed.
Ice cream salt is not mixed in with the ingredients used to make ice cream. In fact, it is not even considered edible, and it never comes in contact with the ice cream. Instead, it is mixed in with ice or ice water, which is placed in an outer chamber of an ice cream maker.
Although ice is cold, it is not cold enough to freeze ice cream. Adding salt makes the ice water mixture a few degrees colder than 32°F (0°C). It does this by lowering the freezing temperature of water as well as the melting temperature of the ice. This results in temperatures below freezing, which are needed to solidify the ice cream.
A large ice cream manufacturer will typically use chemicals like ammonia to freeze ice cream, but homemade ice cream is usually made with salt. Manual and electric ice cream makers are available in which the salt is mixed with ice water and placed into a large outer chamber. The ice cream ingredients are mixed together in a slightly smaller container, which is placed into the center of the larger one. These ingredients are then constantly agitated, either by hand or electricity, until the mixture freezes and thickens.
A commercial ice cream maker is not required to make small batches of homemade ice cream. The ingredients can be mixed in a small, sealable plastic bag that is placed inside a larger bag, along with the salt and ice water. To freeze the ice cream, the larger bag can be shaken and agitated gently.
The other excellent use for ice cream salt is to sprinkle it on concrete steps and sidewalks, to keep them from freezing.
But it's also essential for freezing homemade ice cream, and it takes someone who knows how to freeze ice cream to get the proportion of ice and salt exactly right, to keep the ice cream soft and not grainy.
I don't have that knack, but my dad sure did. He knew exactly when to add ice cream salt and when to add ice. He also knew how much to add. It's a very fine line, but he knew how to do it.