FOOD SCIENCE EXPERIMENT: LIQUID TO SOLID
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The following experiment is designed to supplement activities in already
existing food and nutrition projects. First read the section "Caution-Be
Science Wise" and then help 4-H members work through the experiment.
CAUTION - BE SCIENCE WISE!
Before you begin any science experiment, you should always follow these basic
rules:
1. Be sure to read ALL directions before starting the experiments.
2. In many experiments, a "control" is used. The control is the standard
against which you compare the experimental food.
3. When doing the experiments, keep everything the same as the control except
for the one thing the directions say to change. Use the same size pans,
the same type of bowls and the same mixing speeds. Be sure that just ONE
thing changes each time.
4. Be sure to label each food when conducting these experiments. Use a piece
of masking tape, a marking pencil, a crayon or anything that will help you
remember which food is which. In some experiments, you'll have no trouble
telling the foods apart. In others, the foods may look the same.
5. The experimental food is not meant to be perfect. Since you are purposely
doing something wrong, you can't expect it to be perfect! So it's all
right when something turns out "bad." That's what is SUPPOSED to happen.
6. Not all experiments in food science yield products that can be eaten.
NEVER SAMPLE PRODUCTS IN AN EXPERIMENT UNLESS YOUR LEADER SAYS THEY ARE
SAFE TO EAT.
7. Records are an important part of any scientific project. You should write
down what happens in each experiment. Experiments may not turn out exactly
the same every time. Recording your results will help you and others who
may try to repeat your experiment.
FROM LIQUID TO SOLID
INTRODUCTION
Custard is a mixture of eggs, milk and sugar that has been heated to coagulate
the protein in the eggs and milk. Custards need to be cooked properly or the
egg protein will overcoagulate. In this experiment, you will see what
happens when egg protein overcoagulates. You will also discover the best
method for cooking custard.
INGREDIENTS
3 eggs
1/2 cup sugar
1/8 teaspoon salt
1 teaspoon vanilla extract
2 cups milk
Hot water
EQUIPMENT
6 custard cups or other oven-proof cups
2 baking pans, 2 inches deep
1 quart mixing bowl
Electric beater or rotary egg beater
Measuring cups - liquid and dry
Measuring spoons
2 pot holders
Knife
2 paper plates
Marker
Cooling racks
PROCEDURE
1. Preheat the oven to 350 degrees F.
2. Combine the eggs, sugar, salt and vanilla extract in the mixing bowl with
the beater. Slowly beat in the milk. Divide this mixture equally into the
six custard cups.
3. Place three of the cups in the baking pan and pour HOT water around the
cups to 1 inch deep. Place the other three cups in the other pan but DO
NOT add hot water. Place both pans in the oven.
4. Bake the custards for about 45 minutes. Test the custards baked in water
for doneness by putting the tip of a sharp knife into the center. If the
knife comes out clean, the custards are done. If the knife is coated, let
the custards bake a little longer.
5. Remove both pans from the oven at the same time. Take the cups out of the
water immediately and place on cooling racks. Be careful when taking the
custard cups out of the water. They will be hot! Label one paper plate
"baked in water" and label the other "baked without water." Put the
custards on cooling racks next to the appropriately labeled paper plate.
Let all six cups cool about 20 minutes.
6. Run a knife around the edge of each cup. Turn the custards out onto the
labeled paper plates. Cut each custard in half vertically and record what
you see. Also taste the custards and record any difference in flavor.
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Appearance Texture Flavor
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Baked in water
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Baked without water
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7. See if you can answer these questions based on what you observed:
* Why does the thin liquid custard mixture thicken and set into a firm
product when heated?
* What differences in appearance did you notice between the custards baked
in water and the ones baked without water?
* Which method of baking is the best method for custard? Why?
EXPLANATION
Baked custards should be cooked by placing custard cups in a pan of hot water
to protect the custard from overheating which would cause the egg protein to
overcoagulate. However, to prevent the custard from overcooking, the custard
cups should be removed from the oven and water as soon as the custard
coagulates.
The custard is done or coagulated when the tip of a sharp knife inserted in
the center comes out clean. An overcooked custard will leak liquid when cut
and feel tough to the touch. It also might have small bubbles on the outer
surface and small holes inside. The tops are usually browner on overcooked
baked custards and there may be a slight flavor difference. Overcooking can
produce a carmel-like flavor.
SOURCE: Food Mysteries, Michigan State University
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Updated 8/15/05