Methods of Leavening and the Science Behind Them

Leavening helps baked products rise and develop an airy consistency. In the case of yeast, it also adds to the flavor of the bread that it is baked into. But yeast is not the only form of leavening, there are several others, each with a unique way of achieving that rising action.

What Is Leavening?

Leavening consists of any substance or agent used to ferment dough (i.e. yeast), any material which produces gas to lighten dough (i.e. baking soda), or any method that modifies or lightens dough or batter in some way (i.e. whipping air bubbles into the mixture). Leavening agents are substances or mechanisms designed to cause a foaming action or case air to be incorporated into a dough or batter to make rise, creating a softer, lighter finished product.

The Science Behind Leavening

There are three types of leavening agents that create this rising effect in doughs and batters: biological, chemical, and mechanical leaveners.

Biological leavenersrelease CO₂ into the dough or batter as part of the agent's life cycle. The most common biological leavener is yeast, though some recipes hinge on the use of bacteria to perform the same function. Sourdough techniques use a natural fermentation process to produce the gas that makes the bread rise. Yeast produces ethanol waste products when it comes into contact with a sugar which causes the gas while the sourdough process creates a lactic acid bacteria during fermentation to create the gas. Biological Leaveners include:

· yeast

· bacteria

· the sourdough process

Chemical leaveners use a mixture of chemical compounds (based on a combination of acids and alkali) that release gases (i.e. CO₂) when the chemicals come into contact with heat or a combination of moisture and heat. Baking soda reacts to heat only to create the gas necessary for rising. Baking Powder has two key components, one of which reacts when it comes into contact with moisture, the other reacting to heat. Chemical Leaveners include:

· baking soda

· double acting baking powder

· tartrate baking powder

· phosphate baking powder

Mechanical leavening involves creaming some of the ingredients, which whips air into the batter or dough. The air bubbles expand when coming into contact with heat which cause the rising process. When the baking is done, the expanded air pockets are trapped in the baked product. While the cooling process will cause the air pockets to shrink somewhat, the structure of the finished product will prevent the air bubbles from collapsing altogether. In the case of angel food cake, hanging the cake upside down during the cooling time makes use of gravity to keep the air pockets fully expanded, creating a lighter, fluffier cake. Mechanical Leavening includes:

· creaming the wet ingredients

· whipping air into egg whites or cream

Resources

Webster's Dictionary. Leaven.
http://www.merriam-webster.com/dictionary/leaven

Wikipedia. Leavening Agent.

http://en.wikipedia.org/wiki/Leavening_agent

Fillipone, Peggy Throwbridge. About.com. Leavening - What Is Baking Powder?

http://homecooking.about.com/od/specificfood/a/bakingsoda.htm

Fillipone, Peggy Throwbridge. About.com Leavening - What Is Baking Powder?

http://homecooking.about.com/od/specificfood/a/bakingpowder.htm

Wikipedia. Sourdough.

http://en.wikipedia.org/wiki/Sourdough

Answere.com What Is the Leavening Agent in Soufflés?

http://wiki.answers.com/Q/What_is_the_leavening_agent_in_a_souffle

Braker, Flo. Fine Cooking. When It Comes to Angel Food Cake, God Is in the Details.

http://www.finecooking.com/articles/angel-food-cake.aspx