In December, I watched Lee Hansen, our STEM guru, work with our Learning for Life classroom teachers as he taught them how to teach chemistry by making bread and cake. In education, this activity fits within the common core standard and explores various aspects of yeast and soda-leavened breads, but for me yesterday,it was simple St. Patrick Day fun in the kitchen, because with green food coloring added to white cake and white bread, you get a holiday treat out of this experiment.
Yeast Based Bread Experiment
Yeast is a living organism that grows best on sugar at 100⁰F (37⁰C). Growth occurs by cell division. Active dry yeast, when added to water, activates the cells metabolically and they begin to grow and divide. The CO2 (Carbon Dioxide) is produced by oxidation of the sugar in the water which makes the bubbles you see in bread.
The history of yeast-leavened bread goes back at least 5000 years to ancient Egypt. Yeast bread is called leavened bread. Many breads are unleavened, i.e. made without yeast or inorganic leavening agents such as baking soda or baking powder. Sourdough breads are made with a different species of yeast than is used in this recipe.
Equipment and supplies for yeast based bread experiment
4 cups all-purpose flour
2 teaspoons salt
2 cups lukewarm water
3 teaspoons sugar
2 teaspoons active dry yeast
Butter flavored cooking spray
Small plastic or glass bowl
Large mixing bowl
2 large loaf pans or 2 metal mixing bowls, 1.5-2 quart
2 table forks
Purpose of experiment
To understand how to culture yeast and make bread.
- Make the lukewarm water by mixing ½ cup boiling water with 1.5 cups of cold water.
- Add the sugar to the water and stir to dissolve.
- Sprinkle the yeast over the top of the water and set aside for 10 to 15 minutes. As the yeast begins to grow the mixture will get foamy and begin to produce bubbles of CO2.
- Measure the flour into the large mixing bowl. Make sure to use level cups. Too much flour will make the dough too stiff.
- Add the salt to the flour and mix thoroughly.
- If the yeast mixture is foamy, stir and add to the flour mixture.
- Knead the dough until the mixture is uniform. It should be a sticky, but firm dough.
- Set the oven temperature to 250⁰F, start it, let it run for one minute, and turn it off.
- Cover the bowl with the dough with a damp cloth or plastic wrap and place in the warm oven.
- Let the dough rise in the warm oven for 1-2 hours. It should double in size.
- Remove the dough from the oven.
- Preheat the oven to 400⁰F.
- Spray the loaf pans or metal bowls with baking spray.
- With the forks, divide the dough into two equal portions and transfer the portions to the loaf pans or metal bowls.
- Rotate the dough so it is nicely rounded and coated with the butter spray and spread it so it is evenly spread in the pans or bowls.
- Cover the dough and place in a warm spot, on top of the stove with the oven on works well, or use steps 8 and 9 instead.
- Let it rise for 20-30 minutes, or until it doubles in size.
- Bake for 15 minutes at 400⁰F, then turn the temperature down to 375⁰F and bake an additional 15 minutes.
- The bread is done when the tops appear light brown.
- Remove the bread from the oven an turn the pans upside down on a rack. The loaves should fall out.
- If you wish, you can turn the loaves over and butter the tops of the loaves while they are still hot.
- Slice and enjoy! Because kitchen chemistry is fun!
1 cup of the flour can be replaced with cornmeal, or other flours such as whole wheat. Or, you can add raisins and cinnamon to make cinnamon bread. Other spices and herbs can be used for other flavors.
To make decorations in the finished loaves, use a sharp knife to cut your initials or other decorations into the top of the loaves just before you bake the bread. The loaves can also be baked on cookie sheets to make turtle bread or other animal shapes.
Unleavened breads are usually cooked in thin sheets. Why?
What are the advantages of unleavened breads over leavened breads?
What are the disadvantages of unleavened breads over leavened breads?
Where did bakers get their yeast before the modern convenience of active dry yeast was available?
If you don’t have sugar, what could you use to culture the yeast?
Do some research and reading on bread-making, and write a short report on what you find.
Soda Based Bread Experiment (an excellent apple bundt cake)
Baking powder is made of starch, sodium bicarbonate (NaHCO3), sodium aluminum sulfate (NaAl(SO4)2), and mono-calcium phosphate (Ca(H2PO4) or cream of tartar (potassium hydrogen tartrate, KHC4H4O6). The starch is an anti-caking agent. During cooking, the bicarbonate reacts with the acidic components (aluminum sulfate and dihydrogen phosphate or hydrogen tartrate) to produce CO2 gas that makes the cake rise by creating bubbles in the dough. The reaction is
H+ + HCO3– = H2O + CO2
Baking soda, which is pure sodium bicarbonate, reacts with acids in the apple juice to make more CO2.
Baking soda and baking powder are both leavening agents that produce CO2, but they have different effects on the flavor of baked goods. Bases such as baking soda taste bitter and acids taste sour. The amount of baking soda in this recipe neutralizes the sour flavor of the apple juice. Baking powder contains a stoichiometric amount of acids to react with the baking soda, so it does not affect the flavor. Baking soda is often used in quick breads such as pancakes and biscuits that contain acids such as fruit or buttermilk because of the fast reaction when baking soda is mixed with acids. Baking soda cannot be used in recipes that do not contain acids because the reaction
2NaHCO3 = CO2 +Na2CO3 occurs during baking, and Na2CO3 is extremely bitter.
Cinnamon and other spices are used to provide good flavors in baked goods.
Equipment and supplies for soda based bread experiment
Butter flavor baking spray
2 Large mixing bowls
1 Small bowl for melting butter
1 Large spoon
2 sticks of butter
2 cups of sugar
2 cups all-purpose flour
2 teaspoons baking powder
2 teaspoons baking soda
2 teaspoons ground cinnamon
6 large apples, or 9 medium size apples, or 12 small apples. Because they are more acidic, tart apples such as Granny Smith, Fuji or Gala work best in this recipe.
2 Tablespoons of powdered sugar for decorating the finished cake.
Purpose of experiment
To learn the purpose of each of the ingredients in baked foods.
- Preheat oven to 350⁰F.
- Spray the Bundt pan with the baking spray so the inside is completely covered and set it aside. The cake will stick to bare spots.
- Pour 2 cups of sugar into one of the large mixing bowls.
- In the small bowl, warm the butter so it is mostly liquid, but not entirely melted.
- Add the butter to the sugar.
- Use the mixer on low speed to beat the sugar and butter together until the mixture is smooth and creamy.
- Add the 4 eggs one at a time, and blend into the butter/sugar mixture after each addition.
- In the other large mixing bowl, add the 2 cups flour, 2 teaspoons baking powder, 2 teaspoons baking soda, and 2 teaspoons cinnamon, and mix well.
- Add the flour mixture to the sugar/butter mixture, ½ cup at a time, mixing well and scraping the bowl down after each addition.
- Remove the beaters.
- Do not peel the apples, the peel adds a nice texture to the cake. Core the apples by making four vertical cuts around the core. Discard the cores. Chop the apple slices into about ¼ inch pieces.
- Add the chopped apples to the flour/butter/sugar mixture and mix with the large spoon.
- Spoon the batter into the Bundt pan.
- Bake for about 60 minutes or until a knife inserted into the center comes out clean.
- Remove the pan from the oven and place on a rack to cool. The cake will shrink slightly as it cools and will then be easy to remove from the pan.
- To remove the cake from the pan, place a plate upside down over the pan, place one hand on top of the plate and the other hand under the pan, then turn the whole thing upside down. The cake will drop onto the plate. Lift the pan off.
- Decorate the cake by sprinkling with powdered sugar.
Cakes typically contain a solid fat (butter in this case), sugar, flour, and water in a 1:2:2:1 ratio. In this example, the water is provided by juice that comes from the chopped apples as the cake bakes. Because the fat, sugar, flour and water are not miscible, these must be mixed in the right order so the final batter is homogeneous.
Butter is made of non-polar molecules and sugar is made of polar molecules, so these will not dissolve to form a solution. An emulsion is created when the sugar and butter are mixed together.
Eggs are water and protein, both polar molecules that would not properly mix with the butter and sugar if these were not first emulsified.The molecules of the flour are intermediate in polarity, so the flour mixes easily with the butter/sugar/egg emulsion.
Polar molecules dissolve in water, but not in oils. Non-polar molecules are insoluble in water, but soluble in oils. Food products that contain a mixture of polar and non-polar molecules are usually prepared as emulsions. Make a list of things in the food market that are emulsions.
Solids with bubbles are called foams. This cake is an example of a foam. Make a list of things in the food market that are foams.
Acidic foods taste sour. Make a list of foods that are acidic.
Can you think of any foods that are basic? Why are there few of any basic foods?
List the ingredients in a cake mix from the market. Can you describe the purpose of each one?
Author: Lee Hansen | Saratoga Springs, BYU Chemistry prof. 32 years. More than 300 scientific publications. Children schooled in several states and Canada. Governor’s STEM committee 2 years. Boy Scouts 35 years, current chair of Learning for Life. Developing STEM curricula for 5th – 8th grade.