Home | Procedure | Observations and Questions | Instructor Information

Leavening can either be a result of a biological metabolism (as in yeast risen breads), a mechanical process (like the whipping of egg whites to form a meringue), or a chemical reaction. “The purpose of chemical leavening agents is to aerate a cake mix or dough, thereby making the resulting product light and porous (Sultan, 40).” Chemical leavening agents commonly used in the home kitchen and in the food industry include baking powder, baking soda, and cream of tartar. The following exercise focuses on baking powder.

“Baking powders are mixtures of chemicals varying in nature and composition that react in the presence of moisture and heat to release gas (Sultan, 40).” Baking powders come in two varieties: single-acting and double-acting. Both produce CO₂ as an end product when the reaction takes place.

“Single-acting baking powder begins to react as soon as the chemical gets wet because the acid is soluble in cold liquids (web)”. Mixing cream of tartar, an acid component, with baking soda called formally sodium bicarbonate, a basic component, creates a single-acting baking powder. The mixture when wet reacts in a two step process like this:

NaHCO₃ + KHC₄H₄0₆ → KNaC₄H₄0₆ + H₂CO₃

The CO₂enlarges existing air holes lightening the batter (Beranbaum, 473). In this way the batter expands, then as the heat of the oven evaporates moisture and coagulates proteins the batter sets around the expanded holes.

“Double acting means that part of the reaction takes place when the baking powder comes into contact with liquid and the remainder is activated by heat during baking.” “Double-acting baking powder is able to react twice because it is made with two different acids (web).” “Double-action baking powders are more commonly used and contain sodium aluminum sulfate or sodium acid pyrophosphate and the monocalcium phosphates making a partial solution and minor release of gas at low temperatures with a maximum release of gas at high temperatures (those of the oven). Starch is used as filler to stabilize by keeping the acid salts from contacting and reacting with the bicarbonate of soda if moisture should get into the powder. The amount of starch can be varied to standardize the strength of the baking powder (Sultan, 41).” Calcium carbonate and calcium lactate are know as anticaking-agents. They are used in many dry foods to allow them to flow smoothly and prevent clumping when exposed to moisture form the air.

This table from Baking Science & Technology shows the makeup of four types of baking powders. Sodium bicarbonate is the commonly used basic component, while the acidic component varies in all four types.

(Pyler, 917)

Which type would you identify as being single-acting? Why? Did you notice that corn starch is a commonly used ingredient in all four?

Here are some interesting facts about using baking powder in recipes from famed Food Scientist Shirley Corriher’s book Cookwise:

“Baking soda is four times as strong as baking powder (Corriher, 138).”The general rule is 1 to 1 1/4 teaspoons baking powder or 1/4 to a breath over 1/4 teaspoon baking soda per cup of flour in the recipe (Corriher, 138)Other variables factor in to determining the proper amount of baking powder or soda such as pan size or the weight of additives like fruit (Corriher).

Another fun fact: Did you know the US government regulates baking powder?

The law requires baking powder to produce 12 grams of carbon dioxide for every 100 grams of baking powder used.  Since all of the carbon dioxide comes from the baking soda in baking powder, at least 25 percent of baking powder must be baking soda.

This exercise demonstrates the chemistry and physics involved when using chemical leavening agents in the kitchen to raise doughs and batters. It reinforces the concept of proper measuring provides a demonstration on the mixing of acids and bases. It is designed for high school students studying food science or for culinary students.

Another side skill that could be gained is testing the baking powder for efficacy by simply putting a small amount of water and listening for fizz. If no fizzing occurs the powder should be discarded as it has passed its usability.

Warn students of the risk of working with a hot oven. Oven mitts or hot pads should be provided in order to avoid burn injury.

Other experiments in this series could include mechanical leavening and biological leavening activities. Mechanical leavening involves incorporation of air or manipulation of steam in the mixing process such as when preparing a laminated dough or whipping egg whites into a meringue. Biological leavening agents are primarily yeasts used in bread making.

	Types
	A	B	C	D
Component:	Per cent of total weight:
Sodium Bicarbonate	30	30	30	30
Monocalcium phosphate monohydrate	5		5	12
Sodium acid pyrophosphate	36	42
Sodium aluminum phosphate			26
Sodium aluminum sulfate				23
Calcium lactate	2
Corn starch	27	28	39	28
Calcium carbonate				7

Objectives

Each student team will prepare cupcakes according to the instructions.  Each team will include the mystery ingredient in the recipe as listed in the base recipe.

Team Red:  Mystery ingredient is nothing

Team Blue:  Mystery ingredient is 3 tsp. baking powder

Team Green:  Mystery ingredient is 1/4 tsp. baking powder

Team Yellow:  Mystery ingredient is 1 tsp. baking powder

Base Recipe

3/4 c. + 1 Tbsp. + 1 tsp. flour

1/4 c. butter

1/2 c. sugar

1/4 c. milk

1 egg

1 tsp. vanilla

Mystery ingredient

1.                    Gather necessary equipment.

2.                    Preheat oven to 350°F.

3.                    Line four cups of a six cup muffin tin with four muffin papers.

4.                    Combine flour, sugar, and mystery ingredient in a mixing bowl.  Set aside.

5.                    Cream butter and sugar in another bowl.  Beat in egg, milk, and vanilla.

6.                    Add creamed mixture to dry mix all at once.  Stir only until batter is smooth.

7.                    Spoon batter into paper liners filling 2/3 full.  Bake 15 minutes or until a toothpick can be inserted and removed clean.

It is important to measure correctly. Too much of a leavening agent allows too much carbon dioxide to form too fast, and the cupcake raises too fast and falls before the proteins “set”. Too little leavening agent does not give off enough carbon dioxide and does not raise enough. before the gluten sets.

Objectives, Cautions, and Lesson Plan Suggestions

Objectives

Procedure

Observations

Questions

Answers to Student Questions