Quick and Easy Homemade Ice Cream

This is a favorite demo for small groups (20 or so), but it can be scaled up for large classes or parties.

Make ice cream using liquid nitrogen! The idea for this came from a Scientific American article (Kurti & This-Benckhard, Sci. Amer. 1994, 270 (4), 66-71 I think) on science in the kitchen. It makes good ice cream for two reasons:

1. The mix freezes very quickly, so you get small crystals and a very creamy texture.
2. The evaporating LN₂ aerates (nitrogenates?) the mixture, so it doesn't end up as a frozen lump.

This demo ties in nicely with thermodynamics and phase changes. It's also excellent for receptions, especially when prepared in public.

Liquid Nitrogen Ice Cream (makes about 1/2 gallon)

cream base:

4 cups heavy cream

1 1/2 cups half and half or milk. Milk gives a slightly more crystalline product, so choose the fat; fat free half and half(!) fails miserably (duh)

1 3/4 cups sugar

berry mixture:

1 quart mashed strawberries

1/2 cup sugar

other possible flavors:

1 1/2 quart peaches

3 shots of espresso coffee

1 tablespoon real vanilla extract

Use gloves and goggles when doing anything with liquid nitrogen. Keep all the ingredients cold, and make sure the sugar is dissolved in the cream base before adding the other ingredients.

Pour the cream base into a large bowl. Slowly add one to two liters of liquid nitrogen and stir vigorously with a stout-handled spoon. (Wimpy spoons might will break.) When the cream has thickened, add the berry mixture and more nitrogen. Continue to stir until the nitrogen has evaporated and the fog has disappeared.

This recipe does not keep well, and is best consumed immediately (oh darn). If it begins to melt before everyone is served, simply add more liquid nitrogen and stir.