From the blog October 31, 2011 Grant

Is Liquid Nitrogen Safe?

At the beginning of the MC project, Nathan set out to dispel many of the myths surrounding cooking, yet some common misconceptions about liquid nitrogen still persist. Sometimes we get questions like Is liquid nitrogen dangerous? Will it hurt you? Or, You can’t cook with liquid nitrogen! It’s poisonous!

The truth is, liquid nitrogen is completely inert except for its extreme temperature. It will cause any metal it comes in contact with to become freezing cold, but wearing dry gloves is enough to protect your hands from creating a “tongue stuck to the flagpole” scenario. The liquid nitrogen itself will evaporate before it contacts your skin due to the Leidenfrost effect (see video below).

Actually, liquid nitrogen pales in comparison to the dangers involved in most applications of fryer oil or even sugar. Fryer oil is extremely hot; it spills, it splatters, it splashes. Any cook who works frequently with deep fat fryers gets burned all the time. You get little blisters on your arms and hands when heating oil. The day we shot our wok cutaway photo, Max got all sorts of burns on his arms from tossing the phad Thai and oil so many times.

By the end of this shoot, Max’s arms were full of tiny burns from the hot oil.

When it comes to kitchen burns, sugar is enemy number one. Anyone who has had a close encounter with hot caramel knows that you really don’t want this stuff on your skin. If a little bit of the hot caramelized sugar lands on your hand, your first reaction is to rub it, which leads you to smear it onto your other hand. It just sticks everywhere, and you end up burned all over.

I’ve been working with liquid nitrogen in the kitchen for about five years now. I’ve dipped my bare hands in it, spilled it, splashed it, but never been hurt by it. I’m not saying you should go ahead and goof around with it, but you should give it a chance without fear. Go ahead and try it! It’s great for all sorts of applications. Just put on gloves, wear long pants so that it can’t drip into your shoes if you spill any, and don’t eat food until you’re sure the nitrogen has boiled off of it. (For a more complete discussion, see “Safe Handling of Cryogens,” page 2·464-466 in Modernist Cuisine.)

A number of recipes in Modernist Cuisine use liquid nitrogen to achieve special effects, from firm coating gels to foie gras torchon, from shrimp and grits to buttermilk biscuits. And, of course, we love Nathan’s method of cryofrying meat, which is to cook meat sous vide, then dip it in liquid nitrogen, and finally deep-fry it quickly to get a really nice, Maillardized outer crust with a rare or medium-rare interior. We use this technique in our mushroom cheeseburger recipe. And again, it’s really the hot oil from the deep fryer that you have to watch out for in that recipe.

Wearing gloves when handling liquid nitrogen protects your hands from the cold temperature of the metal container.

Although it’s not hard to handle liquid nitrogen safely, it is also not completely without risk. In fact, I just happen to be one of the few people in the world who have actually had a traumatic experience with the substance. I once used liquid nitrogen at a dinner for some guests and afterward was transporting a Dewar of the stuff in the back of my SUV. Although the Dewar was in perfect condition, some of the dinner guests had been playing with it and hadn’t refastened the lid. I didn’t realize that, and as I was heading up a hill, the Dewar fell over. Liquid nitrogen has a very low viscosity, so it is thinner than water and flows like crazy. It quickly spread all over the bottom of the car, and as it boiled off furiously, the car rapidly filled with vapor. It also got really cold, and I couldn’t see out of my rearview mirror or rear window. It was like driving through the densest fog–but the fog was inside the car!

The correct way to transport liquid nitrogen.

I pulled over and got out of the car as fast as I could. As the nitrogen evaporates into gas, it displaces oxygen in the air, so if a lot of it spills in an enclosed space it can create a suffocation risk. Emerging from the car, I looked back and saw white fog pouring out from every opening. Luckily, our photographer, Ryan Matthew Smith, was behind me and also pulled over. We opened the hatch of the SUV to get the Dewar out, in case it was still leaking. I heard the plastic in the car crackling as it warped from the intense cold.

When it was all over, I was surprised to find that despite the large size of the spill, it didn’t cause any permanent damage. If the Dewar had been filled with superhot fryer oil instead of ultracold liquid nitrogen, it would have been a different story.

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Discussion

  1. Patricia @Cooking Cakes and Chemistry October 31, 2011 Reply

    Great post! I love playing with liquid nitrogen and dry ice! I’ve used a couple of ideas from MC for food chemistry demos (fizzy fruit made in a pressure cooker with dry ice and using whipped cream – i cheat and use it from a can – in liquid nitrogen to make instant ice cream). The guests always love it but I do get the “is it dangerous?” questions too…

  2. Laura @ hip pressure cooking October 31, 2011 Reply

    Fascinating entry on the safe handling of Liquid Nitrogen, but it does not address consuming it.

    I’m reading between the lines that it actually evaporates and your guests are not actually consuming it – but it would be nice to read some scientific data about it not leaving any traces in the food that is actually frozen by it and it’s effect on the DIGESTIVE and not RESPIRATORY system.

    Thanks,

    L

    • CJ the Scuba Instructor November 1, 2011 Reply

      Nitrogen under high pressure can cause narcosis, but unless you’re serving dinner in an underwater habitat, that should be utterly irrelevant. Here on the surface of the earth, nitrogen has no notable effects — after all, the air you’re breathing is about 78% nitrogen.

      As for nitrogen in your digestive tract, that could cause two serious consequences that should *NOT* be ignored. If you have too much nitrogen in your stomach… you might *burp*! (Infants accidentally consume ingest nitrogen, along with some other gases like oxygen and argon, with every feeding and must be purged of this gas by burping or else they may feel uncomfortable and cry.)

      Burping while having dinner could reflect terribly on you as a dinner guest, but the alternative is even more dire. If the nitrogen does not leave through the esophagus via burping, it will inevitably leave through the other end!

      Of course, the residual nitrogen in your food is no different than the nitrogen and oxygen that would fill the same volume had you not prepared it with pure nitrogen, so as long as you don’t wolf down your food, you should be able to avoid the potentially shaming consequences of nitrogen ingestion.

      Now, if you’ll excuse me, I just sneezed and got nitrogen *and* carbon dioxide all over my shirt.

    • Stephen Rynerson November 2, 2011 Reply

      I can’t tell if you’re serious, Laura, but liquid nitrogen is just elemental nitrogen, i.e., the stuff that makes up 78% of the Earth’s atmosphere, supercooled to a liquid state. Nitrogen is naturally present in basically all food products because it’s an essential ingredient in every type of amino acid. Asking about “traces” of nitrogen left in the food is like asking about “traces” of oxygen or carbon in the food — it’s what the food is literally made of at the atomic level. The only risks to the human digestive tract from liquid nitrogen are (a) the extreme cold and (b) the expansion in volume when the liquid nitrogen boils back into a gas. If the food is allowed to warm sufficiently after the application of the liquid nitrogen those risks are eliminated as a matter of basic physics.

    • Elise November 21, 2011 Reply

      Laura may not be fully versed with elemental nitrogen, but I also have similar concerns about the residual compounds that are left in the food after the liquid nitrogen sublimates. As I am a scientist who works with liquid nitrogen, I am familiar with many impurities that in liquid nitrogen from the manufacturing process, including heavy metals. I have also spoken with my suppliers and they have said there is no “food grade” manufacturing process to eliminate some of these impurities. In addition, my supplier is the supplier of liquid nitrogen to many high end restaurants in NYC. Has anyone done any testing as to what is left behind after the liquid sublimates?

      • Damon November 17, 2013 Reply

        Oddly, no one seems to want to answer that one.

  3. kathleen white November 1, 2011 Reply

    Great post! I make goat’s milk ice cream and want to use liquid nitrogen. I am not scared it but discussions are helpful. thanks.

    kathy

  4. Sir William November 25, 2011 Reply

    You have missed an important factor in this discussion. Liquid nitrogen (LNI) is NOT CLEAN, and is NOT FIT for human consumption. Let me explain:

    LNI itself is, of course, totally fine. The problem is that during processing, it cryopumps contaminants like mechanical pump oil from the compressor, which will then get into your food.

    Cryopumping is the process by which gasses or liquids condense onto a cold material. To see this in practice, leave kitchen freezer door for an hour — a fine icy layer will form inside, which is just airborne moisture that has been cryopumped and condensed. The same happens inside the mechanical pumps and compressors that make your LNI.

    If you don’t believe me, just try it. Pour 20 L of LNI into a clean flask, wait for it to evaporate, then wipe the bottom with a clean towel. You will see fine black mist. I wouldn’t want this on my hands, let alone in my mouth!

    • Wayt November 28, 2011 Reply

      Thanks for this interesting point. Indeed, any culinary use that involves a large amount of liquid nitrogen should bear the point above in mind. The nature and amount of contaminants varies from one vendor to another, so if your evaporation tests reveal an unacceptable level of contamination, you might try purchasing LN from a different source.

      For nearly all culinary uses outside of commercial food processing, just a liter or two of LN is plenty to get the job done, and in such cases the amount of contaminants is so small that they are unlikely to be detectable or worrisome.

      At The Cooking Lab, we have prepared and eaten many, many dishes with LN, and have yet to encounter any ill effects or off-flavors.

  5. jay June 23, 2012 Reply

    sounds scary…
    I was searching on the safety of nitrogen because while watching the news there was this portion where a restaurant is serving something i dont know what it was, that had liquid nitrogen included and the diners, young people are like playing with the nitrogen, like they are smoking… having 3 kids i wouldnt want to see any of my children have something like if i know it is dangerous for them… it may look fun but i wouldnt let them..

  6. PyroArrow October 8, 2012 Reply

    Girl has Stomach removed after drinking cocktail made with Liquid Nitrogen!: http://tinyurl.com/9rdnbp9

  7. LL Carter November 2, 2012 Reply

    I was wondering about the ingestion of this stuff as a food preservative. and the level safe to be inside the body. I found the statement and link from Pyroarrow interesting.

  8. Indrajit January 17, 2013 Reply

    Was watching Food Detective – a programme on History Channel showing use of Liquid Nitrogen in Cooking . The word Food Grade Liquid Nitrogen was used several times.

    Wonder if there is really something like Food Grade LN or Normal LN is used for food purposes also . Can someone shade some light on this .

  9. RUBIN January 28, 2013 Reply

    Cooking with liquid nitrogen is safe with a Deliza fountain ! Have a look on this innovation : http://www.deliza.fr and http://www.facebook.com/deliza.fr

  10. Mack August 22, 2012 Reply

    (1) To get K from C, just take the temp in C and add 273.15.(2) To get F from C, use the conversion faotcr F=(1.8 x C) +32Hope that helps!PS A lot of conversions for F to C and C to F use the fraction 5/9, but I prefer the decimal form of 9/5 = 1.8 because then I don’t have to remember when I’m multiplying by 5/9 and when I’m multiplying by 9/5 it’s just easier to say multiply by 1.8 or divide by 1.8. Read a lot on this subject and how bad wounds can get. Urgent attention required

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