Liquid nitrogen ice cream: why not at home

Ice cream made in front of the customer in a cloud of white vapour looks like magic. Liquid nitrogen freezes it in a few dozen seconds, and the result is usually very smooth. Even so, it is a technique that doesn’t belong in a home kitchen. That’s why you won’t find a liquid nitrogen recipe on zmrzka – only an explanation of why not.

What liquid nitrogen is

Nitrogen makes up most of the air we breathe. As a liquid, its boiling point is about −196 °C. At room temperature it evaporates quickly and turns into gas – a small amount of liquid produces a huge volume of gas, roughly 700 times as much at 20 °C.

It’s this extreme cold that makes nitrogen attractive to ice cream makers: the mix freezes almost instantly, the ice crystals have no time to grow and the ice cream is smooth. But the same cold and the same expansion are the source of all the risks.

Why not at home

The main risks:

• Frostbite and cold burns. Brief contact with a droplet may not cause immediate harm, because a thin layer of vapour forms around it. But if nitrogen gets trapped in clothing or a glove, or stays on the skin longer, it causes deep tissue damage.
• Pressure in a closed container. Because the liquid turns into a much larger volume of gas, a closed bottle or jar can explode. Liquid nitrogen is therefore only kept in special containers with a pressure relief valve.
• Lack of oxygen. Evaporated nitrogen displaces air. In a small, unventilated room the proportion of oxygen can drop so far that there is a risk of asphyxiation – with no warning smell or colour.
• Swallowing. If liquid nitrogen gets into the mouth or stomach, it evaporates rapidly, and the sudden increase in gas volume can seriously injure the digestive tract. A well-known case from England in 2012 involved a young woman whose stomach had to be surgically removed after she drank a cocktail containing liquid nitrogen.

What to watch out for when buying it

Nitrogen ice cream and “smoking” desserts turn up at markets, festivals and entertainment venues. In 2018 the US Food and Drug Administration (FDA) publicly warned about the risks of products prepared with liquid nitrogen at the point of sale. Children are most at risk, as they may eat the dessert too soon or inhale the vapour.

When choosing where to buy it, check:

• whether the staff handle the nitrogen wearing gloves and safety goggles,
• whether the ice cream is stirred before serving, with no liquid left,
• whether the stall or shop is well ventilated,
• whether the staff tell you when the product is safe to eat.

How to get smooth ice cream without nitrogen

Nitrogen makes ice cream smooth because it freezes very fast – the ice crystals stay small. You can use the same principle at home, just more safely:

• Chill the mix well and let it age in the fridge for at least 4 hours, ideally overnight. The colder the mix going into the machine, the faster it freezes.
• Freeze the ice cream maker’s bowl thoroughly – for a freezer bowl, at least 24 hours.
• Harden in a shallow metal container in the coldest part of the freezer.
• Balance the sugars and solids following zmrzka’s recipes – the right composition does more for smoothness than any showy technique.

Summary

Liquid nitrogen is a working tool for professionals, not a kitchen ingredient. If you treat yourself to nitrogen ice cream somewhere, wait until the nitrogen has completely evaporated. At home you can get smooth ice cream with a well-chilled mix, a thoroughly frozen machine and a balanced recipe.