Cool Food Science

In class the other day we did something very cool (no pun intended); we made ice cream with liquid nitrogen (okay, so there was a little pun intended). Basically, you put a creme anglaise ice cream base in the bowl of a kitchen aid fitted with a paddle. You have the mixer mixing (i.e. churning) the ice cream. Then you slowly pour in a significant amount of liquid nitrogen.

A scientific aside, liquid nitrogen has a boiling point of -195.8*C (77K or -321*F). If it is kept under pressure, it will boil very slowly, keeping its temperature at a constant -195.8*C. This means that it is very, very cold and will freeze things that touch it on contact. It also means that when it is poured out of its container and hits room temperature air or ice cream base, it will boil and, as the definition of boiling suggests, it will turn to nitrogen gas and float away.

This means that you can pour a flask of liquid nitrogen into the bowl of the mixer and it will freeze the ice cream as the mixer churns it. Because nitrogen is just air (it constitutes about 75% of the atmosphere) you don't need to worry about it touching the ice cream (as you would freon from a conventional ice cream machine). Because it takes a relatively short time to freeze the ice cream, it doesn't churn for very long and you get an exceptionally smooth product. Another benefit is, because liquid nitrogen is so cold, the ice cream is ready to eat right away--you don't need to freeze it to let it harden. One final bonus, it will freeze ice creams that have a lot of liquor in them. Liquor has a low freezing point and can therefore act as an anti-freeze, keeping ice cream with a high quantity of liquor slushy. However, the boiling point of liquid nitrogen is colder than the freezing point of liquor so the ice cream will freeze.

Of course liquid nitrogen can be dangerous, since it is so cold you can easily get freezer burns on your skin if you mishandle it. If you use it in a confined space it can increase the nitrogen in the air to such a high level that you can actually asphyxiate (this wouldn't happen from making one batch of ice cream in a kitchen, but it still seems important to mention, just in case). Since it has potential for being dangerous, we didn't get to make our own batches of ice cream but at least we got to watch Chef Kir act like a mad scientist while he made a batch for the class to try. Speaking of trying it, it tasted just like ice cream, except creamier and denser. In a word, it was excellent!

A blurry picture of the finished product on
the mixer's paddle.