Liquid nitrogen ice cream takes the same ingredients normally used to make ice cream, but is frozen using liquid nitrogen instead of chilling in the freezer. The nitrogen is cold enough to freeze the ingredients in minutes, for an instant treat. Handling the nitrogen requires some basic safety precautions, but making liquid nitrogen ice cream can be quick, easy and fun.
Initially, liquid nitrogen ice cream began as a classroom experiment. Teachers used the technique to get their students excited about science. With the rise of molecular gastronomy, the inclusion of science in cooking practiced by some celebrity chefs, liquid nitrogen ice cream has moved from the laboratory and into the kitchen.
Making liquid nitrogen ice cream begins with an ice cream recipe. Cream, sugar and flavorings are poured into a metal bowl and mixed until blended. Heavier solid pieces such as chocolate or bits of fruit can be added here, or the chef may wait to add them during the freezing process to keep them from settling to the bottom. Once the ingredients are blended, liquid nitrogen is used to freeze the mixture into ice cream.
When handling liquid nitrogen, safety precautions are crucial. Liquid nitrogen is extremely cold, -320° Fahrenheit (-196° Celsius), and exposure can be potentially harmful. Gloves and goggles are a must for anyone handling the nitrogen. A special container called a Dewar is required for safely storing and transporting the nitrogen. People unfamiliar with the chemical should seek out advice, either from the supplier or from a professional who uses liquid nitrogen regularly, for safety tips and precautions.
The chef stirs the mixture while adding a little liquid nitrogen. As it hits the bowl, billowing clouds of fog roll out for an impressive bit of theatrics. The mixture begins to chill and thicken right away. As the fog clears, more nitrogen is added, until the ice cream is completely frozen. A 5:1 ratio of nitrogen to ice cream is usually required, meaning that it takes approximately 5 liters of liquid nitrogen to make 1 liter of ice cream. As soon as the liquid nitrogen ice cream solidifies, it is ready to eat.
While most of the ingredients are available in any grocery store, liquid nitrogen is a little harder to come by. It is commonly used in a variety of industries, including welding and medicine. School laboratories are also likely to have access. For people without an obvious source, an Internet search will provide a list of local suppliers able to provide liquid nitrogen and a Dewar.