Have you ever wondered why in the dessert dish, Baked Alaska, ice cream is able to be heated in the oven without melting?

[6]+?+ [7]= [8]

In this dessert the ice cream is coated with meringue and this meringue acts like insulation (similar to a Styrofoam cup) for the ice cream. [10] Acts Like…. [5]

Objective: Students will learn about the properties of egg white foams, specifically meringue, which allows ice cream to be heated without melting.

Hypothesis: Meringue will act as an insulator to allow ice cream to be baked without melting.

Introduction:

Meringues are confectionaries which have been used in baked and cooked desserts for centuries. Meringues can be used as pie toppings, they make the texture of cakes lighter, icings frothier, cookies crunchier, and they allow soufflés to rise. [2] Meringues are defined as egg white foams, which contain sugar. [1] Egg white is defined as a viscous liquid of colloidally dispersed proteins in water. [1] A Meringue is a foam with egg-white protein a its solid phase. A foam is a substance composed of a mixture of molecules in different phases, which, in the case of meringue, is gas trapped in a solid phase. Globulins, ovomucin, and conalbumin contribute to the ease with which egg whites can be whipped into a fine, foam containing small air cells. [1]

When an egg white is first beaten, layers of ovomucin are sheared from the egg white, which coil to form hollow tubes with the appearance of fibers. [1] During the whipping process, the protein in the egg whites is actually being stretched. [4] Molecules of ovomucin spread in a monomolecular layer at the interface between the air bubbles and the thinning films of liquid around them, and uncoil, which exposes the protein’s reactive R-groups. [1] Molecules of the surface denatured proteins unite through reactive R-groups and work to stabilize the foam. [1] When egg whites are beaten, air bubbles are trapped in the liquid albumen; it becomes foamy, increases 6 to 8 times in volume and stands in peaks. [3] While the foam is being heated, the trapped air cells expand from the heat of the oven and the egg protein coagulates around these air cells, which makes the foam permanent. [3] The liquid albumen forms elastic films around the air bubbles, which form during beating, and the air bubbles are then trapped, as displayed in what you see as a foam. [4]

Fun Fact! Egg whites have a great ability to expand and give volume. However, with the same weight of egg yolk, there is much less elasticity than with egg whites.

Equipment:

þ -Baking Sheet

þ -Aluminum foil

þ -Oven

þ -Ice cream scoop

þ -Standing mixer or hand-held beaters

þ -Egg separator (optional)

þ -Metal bowl

*Fat inhibits the foaming of egg whites, so make sure beaters and bowls are clean and that there is no trace of yolk in the egg whites. Use only metal or glass bowls because plastic bowls tend to absorb fat. [3]

Materials (21 Students):

Egg Whites	21
Sugar	3½ cups
Chocolate Chip Cookies	21
Ice Cream	7 cups

Procedure:

1. Heat the oven to 500^oF

2. Cover the baking sheet with aluminum foil

3. Beat the egg whites until they form soft peaks

4. Add sugar to the beaten egg whites, one tablespoon at a time, and make sure to beat the egg whites after each addition of sugar

5. Continue to beat the egg whites and sugar until the mixture is thick and glossy (Meringue forms)

*This step is extremely important because if the egg whites are under beaten the volume of the finished product will be less than the desired amount. However, if over beaten the egg whites will form clumps which will become difficult to blend with other ingredients and because over beaten egg whites lack elasticity, they will not expand properly when heated. [3]

6. Place the cookies on the baking sheet

7. Place a scoop of ice cream on each cookie

8. Spread meringue thickly over the ice cream, making sure that the ice cream is completely covered with meringue

9. Place the baking sheet in the oven. Bake on the lowest rack of the oven for 3 to 5 minutes or until the meringue is lightly browned

10. Eat right away!

Procedure modified from http://www.clemson.edu/foodscience/PDF%20Downloads/Science%20Experiments/bakeicecream.pdf

[9]

Some things to think about:

Why isn't the ice cream melted?

What properties of the meringue protected the ice cream from being melted?

What is a foam and how does this definition relate to meringues?

How is the function of the meringue in this laboratory exercise similar to that of home insulation?

Sites with useful info:

Bottom line for the best egg white foams:
  Room temperature or heated lightly egg white; easier to denature and foam
  Fresh egg whites
  Start slowly when whisking, build up those bubble
  Increase the speed
Then finish with a bang after incorporating other ingredients
Stop on time…look for the slide and the peak
If you have cooper bowls, use them
Use cream of tartar and sugar for stability (later for sweet flavor)

From http://www2.muw.edu/~jfitzger/page84.html

http://food.oregonstate.edu/learn/egg.html

http://www.baking911.com/pantry/eggs.htm

References:

1. Charley, H. Food Science 2^nd ed. John Wiley and Sons, New York. 1982. pp.329, 334-335

2. Shakespeare, M. The Meringue Cookbook. Van Nostrand Reinhold Comp. New York. 1982. p. 8

3. www.iowaegg.org/allabouteggs/foam.html

4. www.baking911.com/howto/egg_whites_beat.htm

5. www.pslc.ws/macrog/ kidsmac/foams.htm

6. www.ucalgary.ca/.../ CHEM/GenInstBottomFrame.htm

7. www.lpappliances.com/.../ Verona_BIG24b.jpg

8. www.newyorkmetro.com/. ../cake_200.jpg

9. www.allcompu.com/.../ pages/misc/lightbulbman.htm

10. www.texascooking.com/.../ apr98nomoreshells.htm