Liquid nitrogen ice cream sounds like something out of a sci-fi movie where people dress in reflective fabrics and wear HUD-enabled visors. Those unfamiliar to LN2 ice cream—as it is frequently abbreviated to—might even believe that eating liquid nitrogen ice cream includes eating nitrogen, a belief which in turn causes concern over one’s health. In reality however, LN2 ice cream is one of the safest, creamiest, tastiest and most natural ice creams available.
What is liquid nitrogen?
Liquid nitrogen is nitrogen, which has a chemical formula of N2, at its liquid state. Nitrogen’s gaseous state happens to comprise 78% of the Earth’s atmosphere by volume. You breathe in nitrogen on a daily basis, so nitrogen itself is perfectly safe to “eat.” Now, as you may know, compounds or matter have three states—solid, liquid, and gas. Solids are generally the coldest. Liquids are hotter than solids. Gasses are hottest. Matter shifts between each state depending on their temperature. What is unique about nitrogen is the fact that its liquid state turns to gas—boils–at -195ºC or -320ºF. Thus, liquid nitrogen is very cold, and by the time it reaches room temperature, liquid nitrogen will not actually be liquid anymore and have evaporated into the atmosphere.
Concept behind liquid nitrogen ice cream
Ice cream, by definition, is frozen cream, and generally, people make ice cream by exposing cream to a cold surface while stirring the cream in order incorporate air into the mixture. While the traditional method works well, liquid nitrogen provides an alternative and more exciting method of procuring ice cream. By mixing liquid nitrogen into the liquid cream mixture, you can freeze cream and turn it into ice cream without using any other cold surface. When the liquid nitrogen contact touches cream, the cream loses its heat energy to the liquid nitrogen, causing the cream to get colder and liquid nitrogen to get hotter. Once the liquid nitrogen has absorbed enough heat and reached a temperature high enough to boil, the liquid nitrogen turns into a gas and escapes into the atmosphere. The boiling away of liquid nitrogen also causes air cavities to form in the cream mixture, aerating the ice cream and making it more light and fluffy. The whole process can occur in a large metal pot.
How to make liquid nitrogen
You simply use a ratio of 1:1, all the way up to 1:5, ice cream mixture to liquid nitrogen ratio to make LN2 ice cream.
Mint Ice Cream Mixture from AllRecipes
Pour ice cream mixture into large metallic bowl.
Gradually pour liquid nitrogen into bowl while stirring the ice cream and liquid nitrogen mixture.
Keep adding and stirring until the ice cream reaches a desired creaminess.
Safety and Leidenfrost Effect
Working with liquid nitrogen can be dangerous. Though, it is no more dangerous than working with boiling water or a scalding hot pan. Due to the extremely low temperature of liquid nitrogen, frost-related injuries can occur. I have also heard that liquid nitrogen can freeze your hands off—not sure how valid such statement is however. Just remember to handle liquid nitrogen carefully!
Image from Wikipedia
Despite precautions necessary in handling liquid nitrogen, a phenomenon known as the Leidenfrost effect prevents liquid nitrogen from being too dangerous for household use. The Leidenfrost effect describes the phenomenon of liquids coming to contact with a surface that is so hot that part of the liquid instantaneously vaporizes to form a gas cushion between the liquid and the hot surface. For example, the Leidenfrost effect occurs when water droplets hit a scalding hot pan, and the droplets scatter or roll around the pan without boiling off immediately. The reason the water does not boil off is because only the very bottom layer of liquid boils. That layer does not boil “off” however, since it remains trapped between the pan and the liquid.
For liquid nitrogen, the room temperature is “hot” enough for the Leidenfrost effect to occur. Thus, when liquid nitrogen hits the skin, a protective layer of nitrogen gas separates the liquid nitrogen and the skin. The effect does not last forever, so it is still best not to come in contact with liquid nitrogen for more than a few seconds. Just know that liquid nitrogen will not burn you immediately upon contact.
Other applications of liquid nitrogen
Did you know that Dippin’ Dots, the novel dot-shaped ice cream is made by using liquid nitrogen? Droplets of liquid ice cream mixture fall into liquid nitrogen to instantaneously freeze into ice cream while preserving its shape.