Key concepts
Chemistry
Food science
Recipes

Introduction
Have you ever wondered about the purpose of each of the ingredients in your favorite recipes? For example, why is baking powder used in some muffin recipes? How does the baking powder affect how the muffins look, feel and taste? In this science activity, you will use a scientific method to make some cornbread muffins to find out. And then you can decide on the best recipe to use if you want to make cornbread for New Year's Day, which is part of a common tradition in the South.

Background
If you examine the texture of a muffin or a slice of bread, you'll see that the basic structure is a random sort of meshwork that surrounds pockets of air. Without these air spaces, the end result would more closely resemble a brick than bread. The air spaces are created by bubbles of gas (mostly carbon dioxide) produced within the batter during the baking process. Ingredients that produce these bubbles are called leavening agents.

In "quick breads," which have no yeast (and don't require hours for dough to rise), the leavening agent is usually baking powder. Baking powder is typically a mixture of corn starch (which helps keep ingredients dry), sodium bicarbonate (a base, also known as baking soda), sodium aluminum sulfate (an acid) and monocalcium phosphate (another acid). When baking powder dissolves in liquid ingredients, the sodium bicarbonate reacts with the sodium aluminum sulfate and monocalcium phosphate. A product of this chemical reaction is carbon dioxide gas, the leavening for the baked product. As the batter bakes, the carbon dioxide produced by the baking powder makes bubbles in the batter. The bubbles are trapped by the surrounding structure of the batter, mainly supported by proteins in the flour and eggs.

Materials
• Muffin pan that holds at least six muffins
• Paper muffin cups for lining the pan (optional)
• Oven
• Three mixing bowls or other large bowls
• Measuring cups and spoons
• Three-quarters cup of all-purpose flour
• Three-quarters cup of cornmeal
• Three-quarters tablespoon of sugar
• Three teaspoons of baking powder
• Three tablespoons of butter
• Two eggs
• Two small bowls
• Three-quarters cup of milk
• Fork
• Oven mitts
• Cooling rack
• Timer
• Volunteers to taste test! (optional)

Preparation
• Butter the muffin pan or line it with paper muffin cups.
• Preheat the oven to 425 degrees Fahrenheit. Be sure an adult is present to help when using the oven during this activity.
• Prepare three mixing bowls, or other large bowls, with the dry ingredients for making three different batches of muffins. In each bowl, mix together one-quarter cup of all-purpose flour, one-quarter cup of cornmeal and one-quarter tablespoon of sugar. (Do not add any baking powder yet.)
• Melt three tablespoons of butter in a small bowl.
• Lightly beat two eggs in a separate small bowl.

Procedure
• Take one of the mixing bowls you prepared with the dry ingredients. You will add no baking powder to this batter—just go ahead and make a well, or hole, in the center of your dry ingredients, and mix in half of a slightly beaten egg, one-quarter cup of milk and one tablespoon of melted butter. Mix the batter until it is smooth. How do you think the muffins will turn out when baking powder is not added?
• Fill three of the (buttered or paper-lined) muffin cups in the pan about two-thirds full with the batter. Do your best to make each muffin with the same amount of batter, but do not spend too much time on this. 
• Take one of the other mixing bowls you prepared with the dry ingredients and add one teaspoon of baking powder to it. This is the amount of baking powder recommended for this recipe. Similarly mix in half of a slightly beaten egg, one-quarter cup of milk and one tablespoon of melted butter. Mix the batter until it is smooth. Why do you think it's important to bake the muffins shortly after mixing the baking powder with wet ingredients?
• Quickly fill three of the remaining muffin cups in the pan about two-thirds full with this batter, again trying to fill them similarly but without spending too much time on this because the baking powder starts working as soon as it touches liquid.
• Bake at 425 degrees Fahrenheit for 15 to 20 minutes, or until the muffins are nicely browned and baked through. When the muffins are done, place the pan on a cooling rack for a few minutes, and then tip the muffins out. Set them aside for now.
• Take the last mixing bowl you prepared with the dry ingredients and add two teaspoons of baking powder to it. How do you think the muffins will turn out when the batter has extra baking powder? Then similarly mix in half of a slightly beaten egg, one-quarter cup milk and one tablespoon melted butter. Mix the batter until it is smooth. Fill three of the (newly buttered or paper-lined) muffin cups in the pan about two-thirds full with the batter, distributing it equally. Bake the muffins as you did before, and then let the pan cool on a cooling rack again. 
• When all three muffin batches are done, compare how they each look, feel and taste. How do the muffins baked without baking powder compare to the other muffins? How about the muffins baked with extra baking powder? How are the muffins similar and how are they different? Can you explain this in terms of what baking powder does?
• Extra: Try repeating this activity but use different amounts of baking powder. For example, you could try half of a teaspoon or three teaspoons. How does using other amounts of baking powder affect how the muffins turn out?
• Extra: If you have a kitchen scale, you could measure the weight of each muffin, and even calculate their densities by measuring the dimensions of the muffins. How do the weights of the muffins compare to each other? What about their densities? Do your results make sense to you?
• Extra: Pick a different ingredient from the muffin recipe. Do research to understand the function of the ingredient in the recipe, and then predict what will happen when you change the proportion of that ingredient in the recipe. Can you accurately predict how changing the amount of a different ingredient changes how the muffins turn out? 

Observations and results
Did the muffins baked without baking powder turn out shorter and harder than the muffins from the other batches? Were the muffins made with one or two teaspoons of baking powder much more similar to each other? 

Baking powder is a leavening agent that produces carbon dioxide gas during the baking process. The carbon dioxide gas bubbles become trapped in the batter as it bakes, forming air spaces in the resultant muffins. This is why the muffins baked without baking powder should have had many fewer air spaces, which made them flatter and denser than the other muffins. These muffins may have tasted and felt more like bread than fluffy corn muffins. The muffins baked with one teaspoon of baking powder should have seemed like typical corn muffins—they should have been somewhat fluffy with many air spaces. The muffins baked with two teaspoons of baking powder may have seemed very similar to the muffins with one teaspoon of baking powder, indicating that additional baking powder did not make a huge difference in how the muffins turned out. That said, the muffins baked with two teaspoons of baking powder may have seemed slightly fluffier than the ones baked with one teaspoon of baking powder, but overall these muffins should have been much more similar to each other than the ones made with no baking powder.

Cleanup
Enjoy some tasty corn muffins!

More to explore
Leavening Agents, from David W. Brooks, University of Nebraska–Lincoln
What Is the Difference Between Baking Soda & Baking Powder?, from About.com Chemistry
The Difference Between Baking Soda and Baking Powder, from Amanda Greene, Huffington Post
Chemistry of Baking Ingredients 1: How Much Baking Powder Do Quick Breads Need?, from Science Buddies

This activity brought to you in partnership with Science Buddies