Slashdot Mirror
Making Ice Cream With Liquid Nitrogen
JasonMaggini writes "Popular Science has an article on how to whip up a batch of ice cream in 30 seconds or so by using liquid nitrogen. Just the thing for those hot summer days. The article is by Theodore Gray, creator of the ultra-spiffy Periodic Table Table."
I've done this with some friends just last week. It looks quite scary, espesially when the physics buffs start putting the liquid nitrogen in their mouth.
To do this right you need to use more than 30 sec if you do it by hand like we did.
Use 2 eggs, and 0.6L of cream and mix in a bowl.
Chop one 100g dark chocolate bar and mix with the rest.
Add 0.1 L Irish Cream.
Whip it all together while someone pours a small stream of liquid nitrogen into the bowl.
Don't do it to fast (30 sec will give you large frozen lumps...).
When the ice starts to get thick enough, stop pouring nitrogen and put the lid back on the nitrogen container. You can play some more with it *after* you have eaten your ice-cream.
This would be a great idea for a bussines, set up a stall near a beach and sell on-the-fly real ice-cream to tourists. $5 a cup, the show is for free!
- Ost
---- Sig. gone.
Tips (haven't read the article yet, so some of these might be redundant) -
- make sure you have good ventilation.
Nitrogen can fill the room and will push out the good air.
- don't use a regular blender.
Unless you have a heavy duty egg beater the nitrogen will be freezing the ice cream mix so fast that you'll bust the motor. Use a heavy duty one and then switch over to a large metal spoon.
- good ingredents count.
Use good cream. Add powdered milk for the extra protein. (I like adding a little bit of high quality protein that I use while working out) We used fresh dates, strawberries or whatever. If you use vanilla don't use that crappy stuff. Good vanilla is well worth the price - sort of like good basalmic vinegar. Once you've had the real deal the stuff supermarkets sell tastes like crap.
- Invite a bunch of friends.
It's a great party. Do the typical physics/chemistry tricks with the remaining liquid nitrogen. The shattering tomatoe or fake hand in the nitrogen tricks are always classics.
I've done this - it's fun and impresses the girls, but harder in an office/lab than in a well stocked kitchen.
Once my girlfriend was visiting me at work and I was stuck late while I was finishing some experiments. The kitchenette was stocked with only the usual bad coffee gear--ultra-pasteurized cream cups and sugar packets and bad coffee--and she was restless and hungry. I asked if she wanted some ice cream and she thought I was teasing.
So I took one of the vacuum insulated coffee carafes and filled it dramatically with LN2 from roll-around dewar in the lab (any time you crack the liquid feed on one of those things its pretty dramatic with the hissing and the steam and the gurgling and the spattering, dancing beads of LN2). As an aside, vacuum insulated coffee carafes filled with LN2 will hold it for more than a day.
I carried it boiling and fogging back to the kitchenette as she followed at a more than safe distance. I found a plastic bowl in the sink and filled it with the contents of about 100 of those little ultra-pasteurized coffee creamers and about 100 packets of sugar, brewed up a fresh pot of coffee and skimmed the first few seconds worth off - when it actually has some flavor and added it to the bowl. She looked mighty dubious, but the glass liner had cooled enough that the carafe didn't seem dangerous any more so she moved in to watch.
Then while I stirred the mixture with a plastic spoon (and, don't forget - while wearing the bright blue cryogenic safety gloves and full face shields) she poured in the LN2 which filled the bowl with dense fog that poured out, over the counter, and down around our ankles, spreading out across the floor, looking for all the world like a bad sci-fi movie.
In about 30 seconds we had a bowl of half decent coffee ice cream to share.
And, for just a little while, she thought being a geek was really cool...
N2O (nitrous oxide) is used to make instant whipped cream - in a pressurised state it dissolves in fat, so when the pressure is released, it expands in the cream, causing it to go light and fluffy. I'm wondering if N2 might have a similar effect, making the icecream lighter and fluffier than it might normally be? Solubility of N2 in fat? It's non-polar so it should dissolve, no?
Unfortunately N2 don't have the same effect as N2O when inhaled |-)
"I think it would be a good idea" Gandhi, on Western Civilisation
The goal of ice cream is to make the ice crystals really small. Big ice crystals feel grainy in your mouth. Ice cream should be smooth.
Ordinarily, you achieve that by stirring the ice cream constantly. With liquid NO2, you achieve the same effect by freezing everything before the crystals have a chance to grow.
So yeah, you do get better ice cream this way.
There's also a lot less air whipped into it. For my taste, there's too little; a spoonful has too much "cold" in it to really taste it. Since it has more ice cream and less air, you get more mass in a spoonful, and thus more cold. But that's all a matter of taste; that's exactly what Ben and Jerry make all their money at. A little goes a long way.
I'm nots ure, but a professor I knew at Northwestern sometimes gargled with liquid nitrogen to impress people during "chemistry day" type demos. Supposedly if you keep exhaling and moving the stuff around in your mouth, the air is enough of an insulator to keep from freezing your tongue off.
I had lots of fun working as a programmer in an organic chem lab there. When we needed a break from coding, we'd go invent weird chemistry demos or throw defective glassware against the wall. I don't think I'll ever try the liquid nitrogen gargling, though.
-- Laura
What happens there is the Leidenfrost effect in action- the temperature inside your mouth is well above the boiling point of liquid nitrogen (77K, -196 degC, -321 degF, 138.6 degR), so that when the liquid contacts your mouth, a very small amount of it quickly boils off, and creates a layer of vapor between the remaining liquid and the flesh of your mouth. This vapor layer acts as an insulation blanket, allowing you to consume small quantities of liquid nitrogen without flash-freezing your palate.
The Leidenfrost effect is also sometimes demonstrated by wetting your hand with water, and then briefly plunging your hand into a container of molten lead. The same principle applies, as the lead is above the Leidenfrost point of water, so the water will form a vapor layer around your hand that insulates it from the molten lead. As much as I would like to believe that since the same principle applies, this is just as safe as brief exposure to LN2, I'm rather reluctant to try this.
Also, molten lead is a lot harder to come by, for me anyway, than liquid nitrogen- I work at UIUC's helium liquefier, so there's up to 5000 gallons of LN2 right outside the window (used both for providing to research groups and for the helium liquefier itself), and LN2 hoses on the wall. I'm generally pretty cautious with the stuff though- it does sting when it contacts bare skin, and as labels on the dewars often remind me, pure nitrogen DOES NOT SUPPORT LIFE, so you want to make sure that if you use large quantities (and the 220L dewars some groups have qualify) in a ventilated area. I've personally not found working with liquid nitrogen to be very dangerous- it's certainly less dangerous than some of the stuff used in an organic chemistry lab.
I remember the lab manual intro for a chemiluminescence/phosphoresence experiment that used things like polycyclic aromatic hydrocarbons and the solvent DMSO (which isn't terribly toxic by itself, but can be absorbed through the skin, and has a nasty tendency to take other compounds with it), that had a warning that went something like: "Most of the reagents and solvents used in this lab are toxic, flammable, carcinogenic, mutagenic, teratogenic, or some combination thereof." LN2 and LHe are just really, really cold.
Anyway, I've had liquid nitrogen ice cream a number of times before- it tends to be a perennial favorite of many of the science-oriented clubs on campus, as well as a popular demonstration at the annual Engineering Open House- some ChemE's mixed some up this year- using LN2 I poured for them the day before, which was sweet. The ice cream is usually pretty good, IMO. The consistency can be rather variable, and it isn't as good as cranked homemade stuff, but hey- I'm not going to pass up free ice cream.
"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."
A bunch of people have been commenting on the professor who used to gargle LN2. The man's name was Jearl Walker, author of The Flying Circus of Physics, who published an excellent essay describing exactly how to do it. He also talks about dipping your hand in molten lead, as well as walking on fire. He is the one who mentioned that when you let the LN2 touch your teeth, they crack.