Playing With Ice

Liquid Nitrogen Aki Kamozawa and H. Alexander Talbot

In kitchens all around the world, cooks are experimenting with liquid nitrogen. It is a dramatic and very useful culinary tool that can cool or freeze things in an instant. It is made of pure nitrogen in a liquid state. Daniel Rutherford discovered the element nitrogen in 1772. It makes up 78.1% of the earth's atmosphere by volume. In its gaseous state, nitrogen is odorless, colorless, non-flammable, non-toxic, and largely inert. Nitrogen is found in organic materials, foods, explosives, fertilizers, and poisons. The single largest industrial use for nitrogen is combining it with hydrogen to produce ammonia. The ammonia is then used in many different products such as nitric acid, urea, hydrazines, amines, fertilizers and laughing gas.

Liquid nitrogen is a relatively inexpensive cryogenic liquid. It is created by fractional distillation of liquid air. Fractional distillation is the process of separating chemical compounds by their boiling points. Nitrogen has a lower boiling point than oxygen, so it can be distilled and collected from the liquid air first. Liquid nitrogen freezes at -210°C and boils at –195.8°C. It is also notable in that it boils immediately upon contact with warmer temperatures. As it boils it evaporates into nitrogen gas and dissipates into the atmosphere. Inhalation of too much nitrogen can cause dizziness, nausea, loss of consciousness and death, so it is very important to work with liquid nitrogen in well-ventilated areas.

Liquid nitrogen is typically stored in containers called dewars. These cylinders are insulated, vacuum-jacketed pressure containers equipped with safety valve releases and rupture discs to release pressure buildup and prevent explosions. Under normal circumstances, these containers will occasionally vent, so it is important that they be kept in well-ventilated areas. The extremely cold contents mean that any uninsulated metal piping on the cylinder will be at dangerously low temperatures and should not be touched with bare flesh for fear of freezing and tissue damage. Loose-fitting protective gloves, goggles, and face shields are recommended when working with cryogenic liquids.

Join the Kitchen Alchemy team for a class on chilling out with liquid nitrogen at the Astor Center in New York City on August 26! Enter promo code "POPSCI" to get 10% off admission.