The other thing I would worry about is the source of the liquid nitrogen. If you're actively adding LN to something you consume, I'd want to make sure I knew what was in it. I have a feeling that the LN suppliers for welding don't care if nasty stuff gets in their LN (stored in an unclean container).
A long time ago in a galaxy far far away I got to screw around with LN dewars for waveguide pressurization and also extremely high power coax feedline pressurization. You want about 2 or so PSI (varies by system) to keep water out and eliminate all chance of corrosion. The density of liq N2 is such that a small liq tank is the equivalent of a staggeringly large gas N2 pressurization system like the size of a tank car. Also its very hard to explode a liq tank and very easy to explode an ultra high pressure tank by making a mistake with regulators and pipes. A dewar would keep a feedline pressurized for, eh, maybe week, maybe weeks. Some dewars have a better or worse vacuum than others. Boys will be boys and we screwed around with the liq N2 a little. The author got ripped off because in bulk we paid roughly "milk" prices. Supposedly the liq N2 and milk price comparison held for decades at a time in the old days. So his little 20 liter dewar should have cost maybe $20 to fill. Then again, higher energy costs than the 90s, liability insurance, and "we know foodies will pay anything, so lets charge them anything..."
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.
We got price quotes without telling them the application, so I'm pretty sure we're not paying a "foodie" price, but rather a "you're using a super small dewar and so effectively pay way more" penalty.
That person consumed actual liquid nitrogen. The cardinal rule of culinary liquid nitrogen: don't ever serve a guest liquid nitrogen.
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.
Yes. The second cardinal rule: guests don't get to play with LN. Three people at our party were allowed to handle it. I mention this in the post, under "isolation".
I feel really dense asking this, but I don't have the faintest idea how the procedures you've mentioned prevent consumption of liquid nitrogen.
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.
If the LN2 is still liquid, then it is boiling. If you had a pocket of LN2 trapped inside the ice cream, it would boil and you would notice your ice cream venting. If the LN2 was still liquid and dispersed throughout the ice cream, then the ice cream would be -196C and you would not be able to eat it.
As long as your food or drink are not spewing off large amounts of gaseous nitrogen, there should be no liquid nitrogen in them.
I have seen stands at local fairs that make LN ice cream to order. It's pretty neat. I haven't done it, but they have 16 year olds doing it presumably without incident.
There is a stand at the Mount Pleasant Farmers Market in Washington, DC, that does LN ice cream. I've never tried it--partly because I don't eat much ice cream, partly because I don't see the point.
It's a better method of freezing than traditional ice cream makers. Faster freeze = smaller ice crystals = creamier mouthfeel.
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.
I was at a tiki bar last week that served drinks with dry ice in it, with a straw! So, so bad. I don't think you should ever give people dry ice, especially when they've been drinking. But if you did, the theory behind its safety is that it sinks to the bottom, so the drinker couldn't really consume it. But with a straw, if it got to a small enough size you could easily suck a pebble in, and the results would be at best very painful.
Maybe I'm wrong and it's not that dangerous, but I don't think I'd do it if I owned a bar.
I'd recommend it. It's useful if nothing else for the stuff on dilution, cocktail balancing (acid/abv/sugar percentages), and batching. It's helpful even for classic cocktails.
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.
Dumb question. When you're making ice-cream / drinks are you actually mixing liquid nitrogen as an ingredient into these drinks / foods? I thought it was solely an agent to quickly cool things I wasn't aware you were actually ingesting liquid nitrogen. Does it modify the taste at all? Is it safe?
Don't think of it as an ingredient, think of it as "frozen air". Literally, air so cold that it has frozen. That's extrmeley dangerous because it's cold enough to damage your body very very quickly... but at the same time, when it thaws over time?
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.
For anybody thinking of doing this, finding someone who has (serious, lab-setting) experience handling LN2 and can personally supervise would be a really good idea.
I second this. I've had LN ice cream and it was delicious. The process was fun, and no one got hurt. Unfortunately, i think that was more due to luck than to having a protocol for handling the stuff.
Some of my friends from Computer Science House (a terrific organization, btw) have several times annually LN₂ parties where ice cream is made. I have never handled the nitrogen myself but I also can confirm, ice cream made with Liquid Nitrogen is incredibly delicious and probably some of the smoothest ice cream I've ever eaten. Not to mention it's very fun to watch it being made.
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.
Summing up a bunch of comments, rather than littering the thread:
* 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 am very jealous! I have a blog about cocktails and am trying to do every recipe in that book at home. I can't wait to do the LN stuff. I just have to talk Praxair into delivering it to me so I can buy a handful of thermoses rather than a $1,500 dewar. (And god knows how I'm going to get my hands on a food-safe rotovap.) I was even thinking about loading it into a cooler with a spigot on the side.
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.
Tomek here, just to add onto the frozen garnishes point, anything with a good amount of water in it will be an issue here (due to the specific heat of water). This is why cookies and marshmallows can be eaten shortly after being taken out of liquid nitrogen. However, if you froze lemons or limes with LN and put it in your mouth, you're burning your tongue. Dave Arnold explains this here, https://www.youtube.com/watch?v=U6k9a4ikpfo.
Cool stuff. I used to 'play' regularly with LN2 and LHe back in my grad student days (experimental condensed matter physics).
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).
Interesting fact about liquid nitrogen (that I learned from Dave Arnold's book, which is fantastic): liquid nitrogen is ~700x denser than gaseous nitrogen.
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!!
Not just transporting it, but in your kitchen too. A professional kitchen that uses it should have an oxygen monitor so they can evacuate if it goes off.
Also, don't screw a lid onto anything containing it or it becomes a live grenade.
>>liquid nitrogen is ~700x denser than gaseous 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!
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).
"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.
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.
Also remember - any dewar itself, improperly handled, can be a bomb! One professor I worked for hammered this concept into us when we started work in his lab.
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 dewar I bought from Amazon isn't pressurized. It is literally a big thermos. I assume it loses more LN to the atmosphere than a pressurized dewar; on the other hand, the explosion risk isn't big.
Hmm, does the cap screw on tight like a normal thermos? Maybe it's designed to always have a loose cap for venting.
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.
The "cap" is a long styrofoam tube with a plastic top that comes on and off with no resistance (if you upended the dewar, that cap would slide right out).
The non-pressurized LN dewars I've seen had a "plug" that was just a cylinder of foam that slid into the neck of the dewar, with a light plastic cap on top. It was lightweight enough to bob upward at the slightest pressure, releasing gas. It probably had a design with channels such that the lip never sealed completely anyway.
They could easily preserve LN for days. Dewars are impressive.
Wow, I forgot just how many days that was, I see. Though I now remember that one of my labs had a storage dewar full of precious biological samples that was a bigger version of this design, and we only refilled it a couple times a month.
I felt bad about the purchase before we actually used it, but now I'm feeling like it made at least as much sense as the circulator did as a purchase. Malort ice cream!
I do not want to discourage people from playing with cool stuff, but for safety reasons, I would like to give a few examples of what can go wrong:
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(fre...
We did hide the caps for the thermoses. You didn't read that in my post because my post is not an instruction manual. I opted instead to keep it vague, saying instead that sealing LN into a container would kill you.
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.
My lab partner back at university once got a very nasty liquid nitrogen burn. Couldn't use his hand for a few weeks. We even executed emergency procedures swiftly and correctly.
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 true, it is easy to get carried away by the fact that the Leidenfrost effect can protect you from small splashes of nitrogen on your skin. As the demos show, it's even possible to dip a BARE hand in... very briefly. For the love of god, don't do this while wearing a ring or a glove.
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.
Liquid nitrogen can be made on site from the ~80% nitrogen in air. Saw this cool machine at "the" physics show this weekend: http://www.elan2.com/product_elan2office.asp. Probably not exactly cheap, but great for medical offices and others who need a regular supply of the stuff.
http://www.nicecreamfactory.com/ in Arlington, VA makes very good ice cream using LN and KitchenAid mixers. I was actually surprised how casual they are about handling the LN. I don't recall the person who made mine wearing eye protection, but maybe I'm misremembering.
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[ 3.6 ms ] story [ 118 ms ] threadAnyway. 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.
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.
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.
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.
Maybe I'm wrong and it's not that dangerous, but I don't think I'd do it if I owned a bar.
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.
It's nitrogen - the same stuff that's in air, just cold.
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.
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.
* 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").
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.
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).
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!!
Also, don't screw a lid onto anything containing it or it becomes a live grenade.
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).
"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.
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.
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.
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(fre...
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.
http://show.aad.org/annual11/Data/EC/Event/Exhibitors/152/pr...
I've bought nitrotini's at Market Pavilion a few times and they're a neat novelty.
It is a really fun thing to play with, and can even clean your floors, but just like firecrackers, do not contain it.