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Salt is used in ice cream because of a special property it possesses: It lowers the freezing temperature of water. Consider making the most basic ice cream. You would mix together milk or cream, sugar and maybe eggs and some vanilla. But this mixture has to be frozen in order for it to become ice cream. You could try to pack it with ice, but milk just isn't going to freeze at 32 degrees F (0 degrees C), so you're going to need a little help. That's where salt comes in. If you pour salt on ice, it creates a briny mix that has a temperature nearing 0 degrees F (-18 degrees C) -- it's not "solid" like ice is, but it's nonetheless colder! This brine is so cold that it can easily freeze your ice cream mixture.

Given peoples' long-standing love affair with ice cream, it's a lucky thing salt has this particular characteristic. After all, we've been gobbling up ice cream in mass doses for more than 150 years. In 1846, the U.S. was home to the invention of the hand-cranked ice cream freezer. It was just a few years later that the delicious treat was being manufactured to a large scale. While that may have been the beginning of what we see today in the supermarket's long freezer filled with all manner of ice cream flavors, you can actually go all the way back to ancient Rome to find Emperor Nero giving banquet guests cream that had been frozen in snow. Even Thomas Jefferson knew how to make ice cream, having learned how while he was in France. The future author of the Declaration of Independence brought back the recipes he'd learned so he could make his own ice cream. Admittedly, it sounds more a like a very "Ben Franklin" kind of thing to do, but there you have it -- Jefferson was a founding father with a sweet tooth, apparently [source: Dairy Farmers of Canada].