My lab had this huge tank of liquid nitrogen left over from an experiment, with a little bit left in it, just kind of waiting for it to all boil off so we could return the tank (or so I presume). So instead I rounded up a posse and we used it to make ice cream.
Prep
Grabbing ingredients ultimately involved a trek to four separate stores. Costco for milk and cream in-quantity, Shaws for cherries and sprinkles, etc., and an almost-futile search for el-cheapo styrofoam coolers to transport LN from the lab to the kitchen upstairs. Normally you’d use a very well-insulated Dewar flask for this, but we don’t have a Dewar, so a doos will do us. Eventually we found some at K-mart, but had to beg an employee to fetch us a couple from storage (apparently people don’t buy coolers in the middle of winter). Cooler Trek left me about half an hour late to my own shindig, but people were still around.
Making the stuff
As a hedge against possible breakage (and because the styro coolers were a bit on the thin side, K-mart special), two were stacked one inside the other and bonded together with Duct Tape, one bit of equipment my lab always does have in abundance. First challenge now was to get the LN safely out of the tank. We should have a long metal pipe for this, but we don’t. Enlisting the help of TvS, we found what (at room temperature) appeared to be an ideal solution, a hard clear plastic/rubber hose reinforced with thread inside. Shoehorned this onto the tank’s output nozzle (there was some heatgun involved), then let ‘er flow. Maybe half a minute of hissing, and about a drop of LN actually reached the cooler before there was a loud SNAP and the hose shattered.
Plan B: We had someone hold the tape-reinforced cooler pair directly up to the nozzle at an angle, screwed the valve open and crossed our fingers. Hissing, fog, lots of spraying, and eventually LN started to stick around long enough to stay liquid upon hitting the bottom of the cooler and collect there. After getting a nice 4" or so, we shut the valve and ran the cooler upstairs. From there it was pretty straightforward: about a 50/50 mix of milk and heavy cream (or substitute Half and Half), about 1 cup sugar (scale depending how sweet your flavoring is) and 2 tablespoons vanilla extract (according to JR this is critically important; don’t ask me why) to every 10 cups dairy, and of course your flavor ingredients. For the first batch we went with blendered marischino cherries and chocolate chips. We even (with proper supervision of course :P) let the kids in the group scoop out the LN, boiling vigorously in a plastic ladle, and apply it to the ice cream in progress. Dropping a marshmallow Peep into the cooler, extracting and shattering it (incompletely) was also demonstrated. First ice cream batch turned out yummy, and extremely cold.
Once the kids were heading out, we pulled off a fresh cooler of liquid nitrogen and it was decided to give the 2nd batch more of an adult theme. Out came the 1-liter Jug o’ Bailey’s, which was substituted for half of the half and half, and mixed with crushed chocolate bar flakes. Bailey’s (or other booze) ice cream is a special LN treat; due to the alcohol content it can’t be frozen in a conventional ice cream maker or freezer (either well or at all, depending how nippy you make it). This batch was pretty nippy. I think it gave me freezerburn of the tongue however.
More goofing off
Since we still had some LN sizzling away in the cooler (and slightly thinned bloodstreams from Batch #2) some of the berries that didn’t get used in the ice cream wound up in the cooler instead, then on the floor in dozens of pieces. Peep-shattering didn’t work as well (probably due to well-insulating marshmallow fluffiness), but strawberries and blackberries break satisfyingly on impact.
Pictures!
My small video & photo album of the event. There would be more, but guess who forgot his 2gig memory card at home and had to steal a little one out of his gameboy DS? :-P
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