How to make liquid-nitrogen ice cream safely — Speaking of Chemistry

Kerri Jansen: Liquid nitrogen has become a
popular, eye-catching additive for preparing cocktails and frozen snacks like ice cream. But the trendy treats are often served with
a side of questionable safety practices. Take, for example, this vendor that a C&EN
reporter spotted making liquid-nitrogen ice cream without any protective equipment. Chemists know liquid nitrogen can be hazardous
when mishandled. But when handled properly, it can deliver
creamy and delicious ice cream safely. We’ll show you how and give you the scoop
on why ice cream is different from other dangerous subzero snacks. We asked American University’s Matt Hartings,
a C&EN adviser and author of the book “Chemistry in Your Kitchen,” to show us how to make
delicious liquid-nitrogen ice cream while minimizing risk. Kerri: So why make ice cream with liquid nitrogen? What’s the benefit? Matt Hartings: So whenever you make ice cream,
one of the things you’re looking for is really creamy ice cream, right. That’s what makes ice cream good. And so there are two ways to do that. One is you can add chemical additives to help
with the freezing process, and the other is to freeze your ice cream really, really, really
fast. If you freeze your ice cream really fast,
you make small ice crystals. The bigger the ice crystals, the grittier
the ice cream will be. So we want to make really small ice crystals. Kerri: With a temperature of around minus
196 degrees Celsius, liquid nitrogen freezes ice cream fast, yielding tiny ice crystals
and smooth ice cream. But it can also cause frostbite and eye damage
with even brief direct contact. Matt Hartings: I think when a lot of people
make liquid nitrogen ice cream, you get used to it, right? You can control it. But we always try to look to take care of
those instances that you can’t control. Kerri (voice over): Safe handling starts with
using a proper storage vessel, such as this vacuum-insulated Dewar designed to hold extremely
cold liquids. Safety experts recommend storing nitrogen
that’ll be used to make ice cream in clean containers and working with a high-purity
grade of liquid nitrogen to avoid contaminants. Another risk to keep in mind is that evaporated
nitrogen can displace oxygen in the air and lead to asphyxiation. So, make sure you’re making ice cream in
a ventilated space to ensure the gas can disperse. You should also consider the amount of liquid
nitrogen you’ll need to make your particular batch of ice cream. Matt Hartings: So if I have a big container
of liquid nitrogen like this, I need to be better equipped to handle any mishaps with
that large container as opposed to if I have a small container like this where I have minimized
my overall risk from having a small amount of liquid nitrogen. Matt starts by pouring ice cream base–a mixture
of milk, cream, sugar, and flavorings–into the mixing bowl. Matt Hartings: One of the things that also
helps make ice cream creamy is air bubbles, the presence of air bubbles. So really fast mixing also helps make a creamy
ice cream. So here we go. Kerri (voice over): After a few moments of
churning, Matt slowly pours in liquid nitrogen from the large Dewar. He wears a face shield to protect his face
and eyes from splashing liquid nitrogen. He also protects his body by wearing an apron,
long sleeves, and an insulated glove. OSHA, the Occupational Safety & Health Administration,
notes that the glove should be loose-fitting and easily removable in case liquid nitrogen
splashes onto it. OSHA’s standards for personal protective
equipment are the same regardless of whether workers are in an ice cream shop or in a lab. When working with a smaller amount of liquid
nitrogen, less protective safety equipment is required, although Matt still protects
his hand with the insulated glove. Matt continues to add small amounts of liquid
nitrogen to the mixture until it reaches the desired consistency. Matt Hartings: That’s just about right. So the other precaution that you always need
to take whenever you’re serving any sort of food that uses liquid nitrogen or dry ice
or anything like that, you need to make sure that all of that has evaporated or sublimated
by the time that you serve it. You don’t want to serve anything that is
too cold. Kerri (voice over): That was the problem with
the popular treat “Dragon’s Breath” this summer. Vendors would submerge things like cereal
in liquid nitrogen and serve it immediately to customers. Although this enabled people to breathe puffs
of liquid-nitrogen smoke, it also led to severe injuries, according to a recent advisory issued
by the U.S. FDA. The extremely cold morsels can cause burns
inside the mouth and esophagus. The agency urged consumers to avoid these
types of foods prepared at point-of-sale with liquid nitrogen. But, like Matt, the agency told us that as
long as the nitrogen has evaporated completely and the food is no longer at an extremely
low temperature, liquid-nitrogen-frozen treats can be enjoyed safely. Speaking of which… Matt Hartings: There it is, nice, fluffy,
smooth ice cream. Kerri: That’s very creamy. Matt Hartings: Satisfied customer. Kerri: For more sweet ice cream chemistry,
check out Emma Hiolski’s What’s That Stuff article all about the stuff that goes into
your favorite scoop. Do you have a favorite kitchen-chemistry technique? Let us know in the comments!

3 thoughts on “How to make liquid-nitrogen ice cream safely — Speaking of Chemistry

  1. Most people don't recommend gloves because liquid nitrogen can get trapped inside the glove. These safety Nazis are ill informed.

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