Key concepts

Have you ever wondered what makes pancakes so fluffy? Why do pancake recipes always tell you not to overmix the batter? The answers to these questions lie in a protein called gluten. In this activity you'll learn about the chemical processes that make pancakes fluffy—and also why overmixing your pancake batter will result in tough, rubbery and flat pancakes.

Pancake batter is composed of two crucial parts: dry ingredients (usually flour, sugar, baking powder, baking soda and salt) and wet ingredients (usually milk, eggs and butter). Flour contains starch and protein. A starch is like a long chain of simple sugars. An example of a simple sugar is glucose, which is what plants produce to feed themselves in a chemical process called photosynthesis. A protein is a long, chainlike molecule made up of smaller molecules called amino acids. Flour contains a protein called glutenin (or gluten), which is crucial for the formation and structure of pancakes and baked goods. Gluten also provides the "chewy" texture in pancakes and breads.

When the flour is dry, the gluten molecules are nearly immobile, which means that they do not move much. They also do not bond (or "link") to one another. When the flour is moistened with water (or with milk and eggs, which are composed mainly of water), the gluten molecules become active. Wet gluten molecules are elastic and springlike (which means that they can change shape under pressure) and plastic (meaning they can maintain their shapes after being stretched and moved around). When flour is mixed with water, gluten proteins loosen from one another, stretch out and begin to rearrange. Further mixing allows the end of a gluten protein to bond with the end of another gluten protein. As the gluten proteins come in contact with one another, they continue to bond. With additional mixing, the proteins create a tighter and tighter weblike network of proteins that are able to trap air bubbles. When chemical leaveners, such as baking powder, create bubbles in a cooked pancake, the gluten network traps these bubbles and allows a pancake to rise and stay fluffy yet still keep its shape.

Pancake Recipe from

Recipe makes about 12 small pancakes, enough for four to six people.

• One tablespoon (tbsp) lemon juice from one lemon
• Two cups of milk
• Two cups unbleached , all-purpose flour
• Two tbsp granulated sugar
• Two teaspoons (tsp) baking powder
• One-half tsp baking soda
• One-half tsp salt
• One large egg
• Three tbsp butter, melted and cooled slightly
• Two tsp vegetable or canola oil
• Large mixing bowl
• Small mixing bowls
• Rubber spatula
• Griddle or 12-inch nonstick skillet
• Wire whisk
• Measuring spoons
• Dry - ingredient measuring cups
• Liquid - ingredient measuring Cups
• Three labels: "Mixed until combined-lumpy," "Mixed until smooth," "Mixed until smooth + 3–5 minutes"
• Stove top
• Ruler

• Have an adult help you to safely turn on the stove - top burner when you are ready to cook the pancakes.
• Make sure to wash your hands thoroughly both before and after the experiment.
• Remember to clean the kitchen and dirty dishes after the experiment.

• Whisk lemon juice and milk in a medium bowl or large measuring cup; set aside to thicken while preparing other ingredients.
• Whisk together flour, sugar, baking powder, baking soda and salt in the medium bowl labeled "Mixed until combined-lumpy."
• Whisk egg and melted butter into milk until combined. Make a well in the center of the dry ingredients in the "Mixed until combined-lumpy" bowl. Pour in milk mixture and whisk very gently until just combined. Some lumps of flour should remain in the batter; you may see streaks of flour , too. (Do not mix until smooth.)
• Transfer one third of the batter to the bowl labeled "Mixed until smooth," and another third of the original batter to the bowl labeled "Mixed until smooth + 3–5 minutes."
• In the bowl labeled "Mixed until smooth," whisk the batter thoroughly until completely smooth, then stop mixing. What do you notice about this batter?
• In the bowl labeled "Mixed until smooth + 3–5 minutes," whisk the batter thoroughly until completely smooth, and then mix for another three to five minutes. What are the differences among the three bowls of batter? Based on the background information, what do you think will distinguish the three batters in the final cooked pancakes? What do you think is happening to the overmixed batter in the second and third bowls?
• Heat a 12-inch nonstick skillet over medium heat for three to five minutes.
• Add one teaspoon of oil to the skillet or griddle and coat the bottom evenly. Use a measuring cup to scoop batter. From the "Mixed until combined-lumpy" bowl, place one-quarter cup of batter onto two to four spots on the skillet (each pancake will contain one-quarter cup of batter). Cook the pancakes until large bubbles begin to appear. Using a thin, wide spatula, flip pancakes and cook until golden brown on second side. Put the two pancakes on a plate. What do you notice about the pancakes made from the lumpy batter?
• Make observations of the fluffiness and height of the pancakes . (Use a ruler and write down your observations if you would like). How much did they rise? How much did the pancakes spread out on the pan as they cooked? Taste the pancakes and note their flavors and textures. Are the pancakes soft and fluffy? Save one or two of the pancakes to compare with the other batches.
• Cook the "Mixed until smooth" batter in the same manner as the first batch. How are these pancakes different from the pancakes from the lumpy batter? Are they taller or shorter than the first batch of pancakes? How much did they spread out compared with the first batch?
• Put this batch of pancakes next to the first batch and compare height and width. Taste the pancakes and note their flavors and textures. Are they fluffier or tougher than the first batch? How would you describe the texture?
• Cook the "Mixed until smooth + 3–5 minutes" batter in the same manner as the other two batches, making sure the pan or griddle remain at the same heat. How are these pancakes different from the pancakes from the first two batters? Are they taller or shorter than the first two batches of pancakes? How much did they spread out compared with the first and second batches?
• Taste the pancakes and note their flavor and texture. Are they fluffier or tougher than the first and second batches? How would you describe the texture?
• Make sure to turn off the burner completely when you are finished cooking.

Observations and results
When you mixed together the wet and dry ingredients in the first bowl, "Mixed until combined-lumpy," you allowed the gluten proteins to become loose, mobile and perhaps begin to link to one another in a relaxed weblike network. When cooked, the chemical leaveners (the baking powder and baking soda) in the pancakes created large air bubbles. The loose gluten network captured the air bubbles and maintained the each pancake's shape while still keeping it fluffy with air.

In the second and third batches, overmixing the batter until smooth or very smooth overdeveloped the gluten. This means that the gluten organized itself into more tightly wound, side-by-side bonds in a very strong weblike network. So there is more of a tough gluten network than in the first batch, leaving less space for fluffy air pockets in between each gluten protein. The second and third batches of pancakes might have been a little tougher than the first batch. This is because there were fewer and smaller air pockets. You might have observed that the bubbles rising to the top of the pancakes during cooking were rose more slowly and were smaller than the large, frequent bubbles in the first batch of pancakes. You probably also noticed that the second and third batches spread out more on the pan when you poured the batter than did the first batch. This is because overmixing the batter allows for more of those gridlike side-by-side gluten bonds, which make the cooked pancake turn out flatter.

Eat any remaining pancakes—and share with helpers, family and friends.

More to explore
Chemical Reactions and Pancakes, from the Minnesota Science Teachers Education Project
Flat as a Pancake? Exploring Rising in Baked Goods, from the American Chemical Society
Chemistry of Gluten Proteins, from Food Microbiology

This activity brought to you in partnership with CityScience