1st – 6th
Difficulty of Project
$10.00 for cream, bread ingredients, and poster board
Adult supervision may be needed when using the oven and whipping the cream.
Approximate Time to Complete the Project
Fats are often criticized in the press for contributing to obesity and heart disease. However, in addition to being an essential part of a healthy diet, the long chains of carbon and hydrogen atoms found in fats often provide a structural framework that helps bread rise, makes whipped cream, and is essential for flaky pastry. In these experiments, students will explore the effects of fats on bread rising and cream whipping.
The goal is to learn about fats in foods.
Materials and Equipment
- White, unbleached flour
- Heavy cream
- Light cream
- Non-fat light cream
- Non-fat milk
- Bread machine
- Tape measure for measuring the bread
- Stop watch for measuring how long the cream is whipped
- Electric hand mixer
Fats belong in a class of molecules called lipids. There are many different types of lipids, but all of them share a similar chemical structure. All of them have a three-carbon glycerol backbone.Long chains of fatty acids are attached to each of those three carbons.The fatty acid chains can differ in their length and the type of chemical bonds therein. These differences explain why some fats (such as butter) are solid at room temperature and why other fats (such as those in olive oil) are liquid at room temperature.
Although not strict necessary, a small amount of fat is often added to bread dough. This fat coats and lubricates individual strands of protein and helps hold the structure together. As the yeast in bread grows, it gives off bubbles of carbon dioxide, (CO2). As these bubbles expand, they cause the gluten in the dough to stretch. Since slightly lubricated gluten stretches more, dough to which a small amount of fat has been added will rise more. However, it is very important not to add too much fat because excess fat will make the structure weaker and cause it to collapse. A fat content of 3% by weight will produce the greatest leavening action. Students who make multiple loaves of bread with different fat content will observe that bread with too much fat will not rise as much as bread with a tiny amount of fat.
Fats also play a critical role in whipped cream.Commercial products that come in a can or in the freezer section of the grocer’s are little more than an amalgam of chemical stabilizers and air. True whipped cream involves beating air bubbles into high fat cream. When you make whipped cream, air is beaten into the fat globules which stick together, forming a structure around the air. Just as the gluten in bread formed a structure around the bubbles of CO2, fats in whipped cream form a structure around the air bubbles. As students experiment with making whipped cream from heavy cream, light cream and low fat milk, they will appreciate how the different fat content of the ingredients affects the outcome!
- Does bread rise more if the recipe includes a small amount of fat? Why?
- How do the long polymers present in fats help make whipped cream?
- Why is it harder to froth the milk for a latte using low fat milk?
Terms, Concepts and Questions to Start Background Research
- Carbon dioxide
- Add the following to your bread machine: 1 cup of water 3 cups of unbleached white flour ½ tablespoon salt 2 tablespoons sugar 1 tablespoon yeast
- Follow the directions for your bread machine as if you were making regular white bread. When the bread is done, remove it from the bread machine and let it cool.
- Repeat Step 1, but add 2 teaspoons of butter to the ingredients.
- Compare your two loaves of bread. Which rose more? If you have time, experiment by making more loaves with increasing amounts of butter (good amounts to try are 3 and 4 tablespoons of butter). Is there a point where butter stops helping bread rise and has a contrary effect?
- Measure the size of your bread loaves. How long are they? How wide are they? Take pictures!
- Chill a 2 quart metal bowl and the beaters of an electric hand mixer in the freezer for a half hour.
- When the bowl and beaters are chilled, pour 1 cup heavy cream into the bowl and begin whipping with the electric hand mixer. Start at a low speed for the first minute before slowly increasing the speed. Do not use the high speeds! How long does it take to whip the cream? Use your stop watch to measure how long it takes.
- Repeat steps 1 and 2 using light cream. How long does it take to whip the cream?
- Repeat steps 1 and 2 one more time using non-fat milk. Are you able to make whipped cream?
- Take pictures of your whipped cream.Make a table comparing the fat content of the cream to the time needed to whip the cream.