A Liquid Nitrogen Cocktail Party
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* There is no LN present in the final product. LN is literally nitrogen in liquid state, and nitrogen is gaseous at sane temperatures. You add it in relatively small amounts, and it evaporates away. It is absolutely not safe to consume LN.
* Yes: you need to ask your LN supplier if the LN is food-safe. This is an easier thing to verify than that a dewar is food-safe (because who knows where it's been). Our LN source also sourced other culinary applications.
* As I said in the post: guests didn't get to handle LN, which is good, because guests were intoxicated.
* The nitro-muddling technique in L.I. is designed in multiple stages to prevent that from ever happening; for instance, if you shake a drink with LN still in it, you'll hurt yourself before you manage to serve a guest LN. The final product has to be pourable. In fact, LN isn't a component of the drink itself, which is chilled with plain 'ol ice (for the dilutive effect).
* The ice cream recipe is freezing cream and egg and sugar, which are all eminently freezable substances (ie: they start freezing at a relatively high temperature). You drizzle LN into the bowl slowly while slowly running the mixer, and you stop when the mixer starts straining against the ice cream. You're never dumping so much LN into the container that it could settle without fogging the whole bowl up (if you do that, you end up with ice cubes instead of ice cream), so it's obvious when it's evaporated off. We remove the ice cream from the bowl with a silicone spatula, to give you an idea of how frozen (or in this case not frozen) the final product is.
(If it helps you understand, without having had the experience of actually doing it yourself: the first couple doses of LN into the mixing bowl are "eaten" by the custard base, which is still liquid. The bowl starts looking like a smoke machine. You wait for it to clear, so you can actually see what's going on in the bowl. You repeat until the mixer paddle starts leaving trails on the bottom of the bowl. Your intuition is that there could be actual liquid LN in the bowl, but that's not really how it works.)
* An example of an idea that freaked me out and I refused to let happen in my house: people freezing garnishes in LN and adding them to drinks. One of the clearest safety indicators you get with this stuff is "the product you're chilling isn't completely solid" (or, in the case of a drink, "at all solidified or slushy").
I'm curious how much you paid for the 20 liter dewar. Here in London, just renting a dewar as a one-off and filling with culinary-grade LN2 was amazingly expensive (several hundred pounds). I wanted to do some LN2 demos and also LN2 ice cream at my daughters' party, but instead opted for much simpler and cheaper (and less fun) dry ice.
But at least, as you mention, you can be sure it was clean. There's no knowing what nasties a used dewar might have been contaminated with (heavy metals, scary organics, etc).
The cryo-garnishing is cool! I've seen the end result at Aviary. Most of them you wait to thaw anyway. Like separating the citrus or berries into vessicles. Just wait until they aren't hard anymore and then top the drink with them.
So, if you vaporize a moderate amount of liquid in a contained space (e.g. spilling a dewar in a car or elevator): even if you manage to avoid touching the nitrogen itself, the gas can crowd out the oxygen and you can asphyxiate yourself. Since it's odorless and colorless, you probably wouldn't even notice.
So ... if you do try this at home, be especially careful when transporting nitrogen!!
One of the coolest LN2 tricks we used to do at our physics demo days took advantage of this - making bubbles the 'fun way'. Take a big pot of boiling water and add some dish soap. Wearing your protective gear, dump a few liters of LN2 into the water/soap mixture, and see it explosively create 700x its volume in bubbles!
Here's someone doing something similar (he uses room-temp water, not hot, so the bubbles come out 'frozen') https://www.youtube.com/watch?v=X5ZAoHxhihU
On your comment about displacing air - in my actual research (when we weren't making LN2 bubbles) we used alot of Liquid Helium (for reference, LN2 at 77K is about 1/4th room temperature, while LHe at 4.2K is 1/70th room temperature). We'd often have superconducting magnet running with fields up to 10T, which IIRC required nearly 100A of current in the freakishly-thin superconducting magnet wire which was submerged in the bottom of the LHe bath in the cryostat. It's possible that the magnet could 'quench' where part of it goes 'normal', immediately heating up due to the huge current, causing more of the magnet to go normal, causing more heating, which eventually boils off all the LHe, releasing HUGE quantities of He gas into the room. Even something simple like transferring LHe from the storage dewar to our cryostat, or cooling down a cryostat the first time, releases huge amount of He gas into the room. I was glad we had an oxygen meter in the lab (which I demanded our adviser buy, she didn't want to waste the money on it at first).
Also, don't screw a lid onto anything containing it or it becomes a live grenade.
"Since it's odorless and colorless, you probably wouldn't even notice." — I remember being surprised reading a haz-card for liquid nitrogen that said you could suffer serious brain damage from lack of oxygen before noticing anything odd. Humans feel we're suffocating when there's too much CO₂, not when there's too little oxygen.
The nitro-muddling technique in L.I. is designed in multiple stages to prevent that from ever happening; for instance, if you shake a drink with LN still in it, you'll hurt yourself before you manage to serve a guest LN.
You're not wrong, though. You need to know what you're doing or you can hurt people. It's for that reason that we actually didn't play around with the stuff (freezing random stuff and shattering it, for instance); we just followed processes we knew would work.
Maybe I'm wrong and it's not that dangerous, but I don't think I'd do it if I owned a bar.
When chilling a glass, you dump out the LN. OK. That makes some sense. But then when making ice cream, you put LN directly into the bowl while mixing. Huh?
edit: I can see why you don't want to provide too many details. I will just say this story, while very interesting, terrified me.
As long as your food or drink are not spewing off large amounts of gaseous nitrogen, there should be no liquid nitrogen in them.
It's also easier in many ways for them. You don't even have to have freezers, since you're spot freezing everything. It saves you from buying a batch freezer for making it, which is $30,000 used. I'm told that if you're buying LN regularly, the distributor will hook you up with the tank at a low monthly fee. So it's probably much cheaper to start a stand that way.
The downside is it's a little less time-efficient. It's REALLY easy to make a 5 gallon batch of ice cream in a Carpigiani.
As far as dangerous culinary experiences go, the risk if you get it wrong is up there with eating blowfish.
Do not be tempted to do this as your first experience in handling liquid nitrogen. Get to know the stuff first.
http://show.aad.org/annual11/Data/EC/Event/Exhibitors/152/pr...
If you don't know the podcast, then you've got about 160 hours of catching up to do. Dave is a better hacker than you.
Dave is also more entertaining than you.
They do have protocols for handling the stuff, there is always a master of ceremony who is well versed in the process and various modes of failure, and nobody is ever imbibing at these parties (at least not to your knowledge).
I probably shouldn't talk about the cardboard boat making competition and the second part of the competition with depth charges made with liquid nitrogen and soda bottles, but ... oops. You all didn't hear that. Now I'm going on a watch-list for sure, aren't I.
If you store LN in a thermos with a cap that seals the thermos, you've made a time bomb, and thermos shrapnel does not improve the flavor of cocktails.
Yet my PhD adviser did not. Sometime after I graduated, one of my fellow grad students blew up a dewar!! (Luckily no one got hurt).
He obtained an old dewar from another lab, and went through the usual cool-down procedure - evacuate the Outer Vacuum Chamber, fill the LN2 shroud, then pre-cool the main bath with LN2. Stupidly he did not notice there were no pressure relief safety valves!!! (Not only should you verify these exist, but you should also verify they work by slightly pressurizing the dewar.) He put in a bunch of LN2, capped it, and left for the weekend. When he came back, the dewar had exploded, pretty much along the weld seams, strewing the metal body and super-insulation all over the lab.
The first professor I mentioned above made sure we understood all valves and release valves. And also noted that if opened for too long while full with LHe, it's possible ice could form in the dewar neck, below the safety relief valves. Always kept me on my toes while working with LHe (well, that and the fact that LHe burns way worse the LN2 if it makes accidental skin contact).
The dewars I was talking about above hold several hundred liters, are about 5-8 feet tall, and primarily for liquid helium (where evaporation is way more of a factor.
The pressure relief valves were built in to the storage dewar's we would get from LN2 and LHe suppliers, but I don't think the cryostats in our lab had them built in, you needed to add them separately by connecting onto the dewar's main flange. The one my colleague exploded didn't have the extra valve hardware attached, and he just capped it and walked away.
They could easily preserve LN for days. Dewars are impressive.
:)
$500, eh? Hmmmmmmmmmmmmm.
Anyway. Although superficially it sounds shocking that a welding supplier would certify their product as food safe, all their gasses are designed for welding, like welding stainless steel food processing gear. So its safe enough to use anything they sell for industrial use, you'll be OK. If you think they're scared of giving you cooties, they're much more terrified of causing a dairy plant to loose its license. Its clean stuff. Also, they're terrified you or they will "cross the streams" with a O2 supply causing a huge explosion if there's any grease or oil contamination, so you can be absolutely sure nothing oily or burnable ever came near the gear, don't even worry about that class of contaminant. If you think about it, flooding something with N2 specifically to prevent chemical reactions means its not fit for sale unless its ridiculously pure. So it is.
Another chemistry problem is you're looking for something that could end up in the product stream without being filtered out or destroyed by the process gear (or destroying the process gear), so kryptonite is kinda unlikely. Also it has to be liq at liq n2 temps because a gas would blow away and a solid (dirty ice, lets say) would remain stuck to the container. Good luck finding a substance like that. I'm pretty much out of chemistry ideas for a food contaminant.
It's air.
Just like how when you cook things, you often use "burning air". If you eat something burning? You will destroy your insides. The difference is that freakishly-destructive levels of cold don't ruin food nearly as fast as freakishly-destructive levels of hot. If we blasted your food with a rocket-engine, it would be too hot to eat, but it would also be charcoal. If we blasted your food with liquid nitrogen, it would still look like food and would still be edible after it returns to normal temperature, so there'd be more temptation to try to eat it while it's still lethally cold. Hence the danger.
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It's nitrogen - the same stuff that's in air, just cold.
It is a really fun thing to play with, and can even clean your floors, but just like firecrackers, do not contain it.
I've bought nitrotini's at Market Pavilion a few times and they're a neat novelty.
LN expands by 700x when it evaporates and warms up to room temperature. This makes thermoses inherently unsafe for storing LN, because they come with lids. Human experience, and the lid itself, through its design, say: Put this lid on top of the thermos! If you get carried away in the heat of the moment, you might give into this instinct and accidentally put the lid on the thermos. Or someone else who was late and missed the safety briefing. Proper lab equipment, by design, does not come with screw-on tops, for exactly this reason. If you are hosting an LN cocktail party, I propose that you hide, throw away, or destroy the lids for the thermoses. A few years ago a German hobby cook lost his right hand due to putting the lid on his thermos: https://translate.google.com/translate?sl=auto&tl=en&js=y&pr...
Don't ever swallow liquid nitrogen. Once you ingest it (which actually is possible) it will rapidly expand by 700x. If you swallow a tablespoong (15ml), you end up with 10 liters (2 gallons) of gas in your stomach, and it will rupture. Occasionally you'll see YouTube videos of people doing this, but they either don't ingest anything, or very small amounts. I would not ever recommend trying this. Here is an example of the feat going wrong - google "LN ingestion" for more: http://www.ncbi.nlm.nih.gov/pubmed/20065833
Don't put things that have been cooled to liquid nitrogen temperature in your mouth. This is more of a personal story: It was the birthday of one of our lab-members, and he had brought some warm beer. We naively decided to chill the bottles with liquid nitrogen. This made most bottles burst and created huge levels of steam, fun, and what we called "beer popcorn": Beer that had frozen into small nuggets by the violently boiling liquid nitrogen. Eventually the birthday-guy decided to try one of the beer nuggets. As he put it on his tongue, it froze to it. He tried to spit it out, but it froze to his cheek as well. He did not manage to rip it out in time and had nasty cold-burns in his mouth. Fortunately, he was not one to easily be bothered by such injuries, so the party did not end at that moment. But, looking back to it now, the feat very obviously was a bad idea.
Don't transport large amounts (more than a few liters) of LN in small enclosed spaces (a car with the windows rolled down, a small basement room). If the container tips and the gas rapidly boils away, it can dilute the oxygen in the room to dangerously low levels. Danger starts below 17% or so.
Small splashes of nitrogen won't hurt your hand, but they can hurt your eye. The cornea of the eye is quite sensitve and (since it has no blood vessels) heals quite poorly. Most people (not all) recommend safety googles.
LN easily soaks through fabrics - also pretty much all of the fancy "cryo"-gloves that you can buy in lab equipment stores. While they look like they might be the right protection for submerging your hands in LN to grab whatever stuff that fell into the dewar - they won't help.
Touching objects that have been cooled with LN can hurt. If the metals conduct heat well (metals, for example), they can hurt you more quickly than you would expect. You can get nasty cold-burns this way. It is good practice to wear protective gloves (although I sometimes leave them off if bulky gloves makes handling the ultracold equipment less safe.)
All in all, have fun playing with LN! But I recommend to start with some simpler experiments(freezing roses and smashing them, ...) first, and then work your way up to food, and then to alcohol. Be paranoid about pressure buildups and prevent them by design of the vessels that hold your LN.
The point of the thermos is to keep a relatively small amount of LN in your workspace, so that the bulk of it can be kept out of the house entirely. The thermos is itself a safety measure.
It was a freak accident, but since then I always cringe when I see articles like this that have little mention of the dangers involved and appropriate safety measures.
It's objects that are the problem, because they do not evaporate and they do not flow away. One of the worst is cloth, which tends to be wrapped around your skin, so when it gets soaked in LN it promptly gets super cold and then sits there burning you while you try to get it off. I got a tiny splash on one of my socks once. Fortunately it wasn't a big enough splash to do more than sting a lot and teach me never to splash LN on my clothing again.
And, as you point out, the other problem is that protective gloves are essential for handling cold solid objects, but very dangerous to have on your hands when touching the liquid. Which means you need tongs! Long tongs, so that your gloved hand stays safely at one end while the other end is fishing around in the nitrogen.
Most of the stuff in it is not dangerous. However unless they're nerdy and willing to spend, they're not going to get much out of the modernist stuff. I'd say bare minimum you need to build a home carbonation rig (~$150ish) or buy an ISI Whip and some CO2/N20 cartridges (similar price all-in) and some Pectinex Ultra-SPL ($15 after shipping) to do anything interesting.