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Science In A Scoop: Making Liquid Nitrogen Ice Cream

Robyn Sue Fisher wants you to know that she would never cook with chemicals. Smitten, her ice cream shop in San Francisco's Hayes Valley, may at moments resemble a high school chemistry lab, but that's because Fisher uses liquid nitrogen to freeze her product.

"Nitrogen is not a chemical," she says. "It's a natural element. It's all around us."

What makes it essential to Smitten is the ability to make ice cream fresh to order. You walk up and ask for a chocolate, or a blood orange with pistachio. The liquid nitrogen freezes the ingredients together, and your cup or cone is ready about a minute later.

Each serving is made from only a few ingredients — including none of the gums, egg yolks or other emulsifiers normally needed to keep ice cream frozen on its months-long journey from manufacturer to distributor to store to your home freezer.

The mint chip, for example, contains just organic cream and milk, mint and a dash of salt. The first lick is like biting into a mint leaf.

"This is the best ice cream I ever had," says my son, who is only 7 but already an experienced ice cream taster, as he spoons his way through an order of chocolate.

He's not alone in his opinion. At the end of a recent Saturday afternoon that was sunny but not particularly warm, there was a steady line of people eager to order at Smitten, which is located in a repurposed shipping container.

Smitten charges a buck an ounce, but a small amount of the stuff is rich enough to satisfy.

"Knowing there are only a few ingredients makes me feel like I can indulge," says Claire Kensington, the founder of a food, fashion and sex website, who'd returned two days after her last serving for some more mint chip.

Of course, there's nothing new about making ice cream with liquid nitrogen. In fact, cooking with the gas has become so trendy lately that Wired felt inspired to put together this how-to guide. (As we reported last year, sometimes these culinary experiments can go dangerously wrong.)

At New York's Eleven Madison Park, guests brought back to the kitchen after dinner are treated to an apple-and-brandy cocktail topped with a frozen dome of foam fashioned with liquid nitrogen.

"It gives us the opportunity to do a little performance before the guests that's really easy and quick, and at the same time entertaining," says Angela Pinkerton, the restaurant's head pastry chef. "Liquid nitrogen is fun to watch, and everyone's curious about it. It looks cool."

It does look (and feel) cool when clouds of gas come pouring out of the metal containers where the ice cream's stirring at Smitten. Fisher started serving ice cream out of a kid's red wagon back in 2009. She spent years developing a patented machine that keeps her ingredients churning in a safe, controlled environment. (She goes into the techie details in this video.)

The stirring, along with the minus 321 F temperature of the gas, keeps ice crystals from forming and is responsible for Smitten's smooth texture, which my son likens to a cross between standard-issue ice cream and whipped cream.

"Because it is a different texture than any other ice cream," says Kensington, "it feels like a new experience, like a new treat."

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

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