The Secret of the Rising Bread
FOOD EXPERIMENT: RISING BREAD
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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.
THE SECRET OF THE RISING BREAD
Flour made from wheat or rye is used to make bread. Did you ever wonder how a
lump of bread dough made from flour and other ingredients ends up as a light
and delicious loaf of bread? What makes bread rise?
Besides flour, some kinds of bread also have yeast as an ingredient. Yeast is
a living plant! Under the right conditions, yeast may use sugars as food,
and carbon dioxide gas is produced as a result. What does that have to do
with bread rising? Try this experiment to solve a food science mystery!
INGREDIENTS
3 packages active dry yeast (not the rapid rising type)
3/4 teaspoon sugar
1 cup ice water
1 cup warm water (100 to 115 degrees F)
1 cup boiling water
EQUIPMENT
3 empty soft drink bottles (16 oz. each), rinsed
3 deflated balloons, same size
Funnel
Masking tape
Marker
Measuring cup - liquid
Measuring spoons
Clock
PROCEDURE
1. Using masking tape and a marker, label each bottle with the temperature of
the water to be used (ice, warm, boiling).
2. Use the funnel to empty the contents of one package of dry yeast and 1/4
teaspoon sugar into each bottle.
3. Add the water to match the temperature on the label. Have the boiling
water ready before starting to add water to any of the bottles. Be careful
when adding the boiling water.
4. Immediately put a balloon over the top of each bottle. Swirl or shake each
bottle GENTLY. Be careful not to spill the boiling water since it could
burn you.
5. Look at the clock and write down the time when step 4 was completed.
6. Let the bottles stand undisturbed at room temperature. Get ready to
observe any differences in the sizes of the balloons. Record what you see
by listing the changes in the sizes of the balloons at different times. Do
they get large or stay small?
Time 5 min. 15 min. 30 min. 45 min.
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Ice water and yeast
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Warm water and yeast
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Boiling water and yeast
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7. See if you can answer these questions based on what you observed:
* What caused the balloon to inflate?
* Did the amount of gas produced vary with the different water
temperatures? If yes, which water temperature produced the most gas?
Why do you think this happened?
* Did the amount of gas produced vary with the amount of time? If yes, why
do you think this happened?
* What did you discover from this experiment that will help you when making
yeast breads?
EXPLANATION: THE SECRET OF THE RISING BREAD
Since yeast is a living plant, it is sensitive to temperature. Cold
temperatures slow down the production of carbon dioxide gas by the yeast.
Warm temperatures are best for yeast to grow and produce carbon dioxide gas,
which makes the balloon get larger. Temperatures that are too hot will kill
the yeast, so no carbon dioxide will be produced. When yeast grows and
produces carbon dioxide in bread dough, the gas is trapped in the dough and
the bread rises. This explains how you end up with a light loaf of bread!
SOURCE: Food Mysteries, Michigan State University
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Updated 8/15/05