Lesson 4 SCIENCE IN THE KITCHEN
or Easy Eggsperiments

Classroom time: 40 to 50 minutes

LESSON OBJECTIVES

Students will be able to:

identify the special properties and functions of eggs in recipes.

CONTENT SKILLS

  1. math: measuring, graphing and estimating

  2. science: observing, recording and concluding

  3. language arts: vocabulary and spelling

MATERIALS NEEDED

  1. cooking equipment

  2. foods for recipe preparation and eggsperiments

  3. Science in the Kitchen or Easy Eggsperiments (activity sheet 5)

  4. Food Safety Mystery (activity sheet 4)

  5. cookbooks, optional

LESSON BACKGROUND INFORMATION

     In addition to the basic ways eggs can be prepared, they also perform in other ways for the knowledgeable cook. Their cooking properties are so varied that eggs have been called the "cement that holds together the castle of cuisine".

     Emulsifiers stabilize mixtures so they don’t separate. One common way that eggs are used as an emulsifier is in making mayonnaise. Eggs keep the fat (oil) and the liquid (vinegar or lemon juice) of the mayonnaise evenly blended together. If egg yolks weren’t used to emulsify the mayonnaise, the heavier liquid would sink and the lighter fat would float just as they do in vinegar and oil dressing. The dressing, when shaken, is a temporary suspension. The mayonnaise is a more permanent suspension called an emulsion.

Coagulation occurs when a substance changes from a liquid to a semi-solid or solid. In a quiche or custard, the ability of eggs to coagulate when heated turns an egg-and-milk mixture from a liquid into a semi-solid. Eggs also turn from a liquid to a semi-solid when you scramble them and, because heat is used for a longer time, change all the way from a liquid to a solid when you hard cook them.

     Many recipes count on the ability of eggs to leaven. When eggs are beaten, a foam of tiny air bubbles is formed. The foam lightens the mixture and increases its volume. When beaten, egg whites will form more foam than egg yolks, so the whites are often beaten separately. Up to a point, the longer the whites are beaten, the more they will foam. If egg-white foam is put into a recipe that’s heated, the air bubbles will expand and the egg white’s protein will coagulate around the air bubbles. The coagulated egg-white protein will trap the air bubbles in the cooked or baked dish and make it light and airy. This process is called leavening. Egg white foams are used to leaven dishes such as cakes, meringues, puffy omelets and souffles.

     When beaten whole eggs, whites or yolks are brushed onto a food as a coating or glazing, they form a shiny, "crusty" layer on the top of the food after it’s baked. If, before baking, other ingredients – such as chopped nuts or seeds – are sprinkled on top of the egg coating, the ingredients will be held in place by the coagulated egg.

LESSON PROCEDURE

  1. Using lesson background information, define and discuss with students the words suspension, emulsification, coagulation, leavening, coating and glazing; explain their application to eggs.

  2. Divide students into three teams. Using the Science in the Kitchen and Food Safety Mystery activity sheets, assign one of the following eggsperiments to each team: Suspension/ emulsification, coagulation or leavening. Have each team perform its eggsperiment and, on a separate sheet of paper, record observations both before and after the eggs are added, cooked or beaten.

  3. As a class, discuss the final results of each team.

EGGSTENSION ACTIVITIES

  1. Have students sprinkle sesame seeds on uncooked, plain, ready-made biscuit or roll dough and on dough glazed with beaten egg. Bake. Then, compare the number of seeds remaining on the rolls.

  2. Have students research cookbooks for additional recipes containing eggs and identify which cooking function the eggs perform in the recipe.