Liquid+Nitrogen+Ice+Cream

=Making Ice Cream: A Lesson in Food Science and Changes of State= (Good for up to 25 kids)

Recipe

 * 1 quart Half & Half
 * 1/2 cup sugar
 * 1 tablespoon vanilla
 * Food coloring (optional)
 * Toppings for fun

Equipment

 * 3 ounce cups and spoons for eating
 * 2 plastic or metal bowls (do not use glass, ever) (recommended size: 2 – 3 quart)
 * 1 very sturdy spoon (wood works great, metal bends and plastic breaks)
 * 1 vacuum insulated container (dewer or thermos)
 * 2 liters of liquid nitrogen
 * Cloth gloves covered with rubber gloves
 * Safety goggles
 * Optional: dry ice (solid carbon dioxide)

=Procedure=
 * Mix half & half, sugar, vanilla and food coloring in one of the bowls.
 * Pour a small amount (about 1-2 cups) of the mixture into the other bowl. Add liquid nitrogen slowly, while stirring quickly, until the ice cream reaches the desired consistency. Dispense this amount and repeat.
 * Do not try to make too big of a batch at once, and do not use too deep a bowl. If the boiling nitrogen cannot escape quickly enough, it will cause the ice cream to froth, leading to a large, sticky spill! (Just ask Charlie). Start with small batches, and work up to larger ones as you go.

1. __Liquid Nitrogen__ temperature is -195.79 ° [|C] or -320.42 °F and is consequently dangerous for that reason. It is the substance used by physicians to freeze of warts so it will damage the skin. Preventative measures include putting distance between the preparation table and the audience and wearing safety goggles, gloves and closed-toes shoes. 2. __Liquid nitrogen__ is in fact a liquid and can soak into cloth. It is therefore recommended that plastic gloves be worn over cloth gloves for maximum protection. 3. If a __Liquid Nitrogen__ spill occurs, clear the area of the spill and allow it to evaporate. The gas does not pose a major risk (nitrogen is already 78% of the air we breathe) if the experiment is performed in a room comparable in size to an average classroom. 4. __Liquid Nitrogen__ should not be stored in the passenger compartment of a transportation vehicle. 5. **Glass bowls should never be used with liquid nitrogen.** They will break. 6. __Dry Ice__ temperature is -78.5 [|°C] or -109.3 [|°F] and can cause damage to skin. The same precautions should be used in the handling of dry ice as with Liquid Nitrogen. Dry ice will also sublime to form carbon dioxide gas, which in a sufficiently ventilated area, should not be a danger.
 * Safety**


 * Discussion Topics**
 * 1) Food Science in the kitchen is something you can enjoy at home with your parents. Mixing foods with specific tastes can result in exciting new flavors.
 * 2) Changes of State Concepts and Vocabulary:
 * 3) Nitrogen is a //gas// at room temperature. Nitrogen is a //liquid// at very cold temperatures. It is generated for use by distillation of cooled liquid air.
 * 4) Sugar //dissolves// in the //liquid// mixture of milk and vanilla.
 * 5) Ice-cream mixture changes from //liquid// to //solid//.
 * 6) Dry ice //sublimes// from //solid// to //gas// (it is called ‘dry’ ice because it skips the //liquid// state).
 * 7) Water from the air //condenses// from a //gas// to a //liquid// on the sides of the bowl.

Adapted from Bevin C. Daglen 2005

Links:
[|The Institute for Liquid Nitrogen Ice Cream Experimental Studies] (one of Charlie's old professors)