Bryn Mawr Chemistry Professor Michelle Francl's recipe for Liquid Nitrogen Vanilla Ice Cream:
4 liters of half and half
1 liter of heavy cream
750 grams of sugar
60 ml of vanilla extract
10 liters of liquid nitrogen
Mix first four ingredients in a large metal bowl. Slowly whisk in liquid nitrogen until mixture freezes. Wear appropriate safety gear! Serve immediately with whipped cream, chocolate sauce and sprinkles.
Makes about 100 small servings.
View photos online here.
Students in Michelle Francl's Chemistry 103 Class have been looking at molecular structure in recent weeks. As an end-of-semester treat, Francl decided to use the creation of "Liquid Nitrogen Vanilla Ice Cream" to help solidify (although hopefully not so much that you can't eat it) the concepts being discussed.
"I wanted the students to think about how the structures of individual molecules could be related to their macroscopic properties," said Francl in explaining the activity. "Why is nitrogen a gas at room temperature, but H2O a liquid? Why can you smell vanilla as soon as I open the container?"
Francl also gave a more detailed explanation of the science at work in her recipe.
"What I did was use a simple ice cream recipe (cream, milk, vanilla, and sugar) to vaporize liquid nitrogen which simultaneously (and rapidly) freezes the ice cream. The liquid nitrogen is at 77 K (-321 degrees Fahrenheit!) and the energy to warm it up comes from the room temperature ice cream mixture (and the warm air of the room, too). The liquid nitrogen turns into gaseous nitrogen (which is all around us - 80% of air is nitrogen) and leaves behind the solid ice cream, which is now safe to eat."
And judging from the response of students, tasty too.