Some of us are getting together to make ice cream with liquid nitrogen I have left over from one of the Harvard labs. Are you in?” How could I turn down an invitation like that? I’ve been dying to get my hands on some LN2 for months, ever since I found a recipe for Dippin’ Dots, the official ice cream of science museums. (The company is now defunct, so it’s back to dehydrated “astronaut ice cream” for science-approved sugar overdoses. The recipe is no longer available online, but you can watch the Top Secret Recipe episode here. Yes, I watched something on Country Music Television.)
To prepare for the big day, I made four quarts of ice cream base: one each of chocolate, vanilla, strawberry, and banana – the flavor combination for the Dippin’ Dots banana split. These were not my usual quality egg custard bases, they were uncooked mixtures of milk, cream, fat-free half and half, and flavor extracts (for everything except the chocolate, which used Fox’s U-Bet chocolate syrup).
As I prepared these ingredients, it occurred to me to try a flavor combination that was more savory. I decided on basil and mozzarella ice creams, and the tomato sorbet recipe from The French Laundry Cookbook. Armed with seven quarts of ice cream base, a few tools, and a cooler full of dry ice, I set out for my rendezvous with extreme cold.
My makeshift freezing setup consisted of a metal mixing bowl set in a styrofoam box, a strainer that just fit in the bowl, and a styrofoam cup with ten holes punched through the bottom. Once I filled the bowl with the LN2, I poured some of the basil base into the cup, held it over the bowl, and let it drip down.
After a few minutes I strained out the basil dots.
You can see from the variation in sizes that producing consistent dots would require hours of trial and error in which I varied the size of the holes in the cup, the height from which the drops fell, and the viscosity of the base. I didn’t have the time or nitrogen to figure that out on the fly, so I did the best I could with what I had. After about half an hour I had a decent amount of “caprese salad” and “banana split.”
The banana and strawberry dots clumped together a lot more than the other flavors. The fat free half and half, which relies on added carrageenan to create a “fatty” mouthfeel, didn’t make the bases as viscous as the custards, so the liquid streamed rather than dripped. Again, smaller holes would have fixed that problem, but at the expense of longer drip times.
I served the salad to various friends and ice cream experts, who agreed that it tasted as advertised. The best compliment I received about the banana split was that it perfectly captured the taste of the cheap ice cream of our childhoods.
I was left with most of the bases and a cooler full of dry ice, which led to an evening’s worth of quick ice cream making. I pulverized the dry ice into bits no larger than a pea, and mixed in about three quarters of a cup per quart of base in three separate additions.
As the base chilled down, I could see that it was heavily carbonated.
After three minutes, the ice cream reached the corect consistency.
He Who Will Not Be Ignored got involved, insisting on mixing the ice into the remaining six quarts.
Straight out of the mixing bowl the ice cream was still mildly carbonated. After an overnight stay in the freezer with the lids cracked open, the remaining CO2 sublimated, leaving behind a perfectly aerated batch of ice cream. I plan on using the savory flavors as a salad course for a summer meal, and the rest as cheap ice cream for the kids. In the meantime, I’m thinking bout how to streamline the process, with this tool being the obvious way to improve the dot consistency. Theres’ still that pesky detail of having regular access to liquid nitrogen, but I’m sure a solution will present itself.