1. Mise en Place for Baking
  2. Essential Baking Equipment and Their Uses
  3. Common Baking Terminology Definitions
  4. How to Measure for Baking: Weight vs Volume Measurement
  5. The Function of Sugar in Baking
  6. The Function of Flour in Baking
  7. All About Gluten and its Role in Baking
  8. All About Leavening in Baking
  9. All About Eggs and Their Function in Baking
  10. All About Fat and its Function in Baking
  11. Ingredient Temperature Guidelines for Baking
Text image saying "Baking Fundamentals Lesson #9: All About Leavening"

All About Leavening in Baking Lesson Overview:

Today we are reviewing a very important topic in baking: leavening. If you’ve ever baked anything before you are likely somewhat familiar with what leavening is, but today we will review what leaven means exactly and all of the different forms of leavening.

Watch the Video Lesson

What is Leavening?

Leavening refers to the gasses that are trapped in a baked good when it is baked. There are numerous ways baked goods are leavened. At times certain ingredients, like baking soda and baking powder, are used to cause chemical reactions in the baked good which leavens it. Other times, the mixing method forces air into the baked good to leaven it. Whatever the method, leavening is an essential part of baking.

Kinds of Leavening

There are 3 main categories of leavening:

  • Chemical Leavening (Baking Powder & Baking Soda)
  • Biological Leavening (Yeast)
  • Physical Leavening (Air & Steam)

Baking Soda & Baking Powder

Baking soda and baking powder are both forms of chemical leavening. This means that that when they are added to a baked good, a chemical reaction begins to occur producing carbon dioxide. This gas gets trapped in the structure of the baked good, leavening it.

Baking powder and baking soda
Chemical Leavening

Baking soda, also known as sodium bicarbonate or bicarbonate of soda, is alkaline in nature on the ph scale. This means that it needs an acidic ingredient to react with in order to leaven the baked good. Common baking ingredients that are acidic include: buttermilk, brown sugar, chocolate, molasses, lemon juice, and natural cocoa powder (dutch processed cocoa powder is not acidic).

While baking soda must be used in a recipe that contains an acidic ingredient in order to be effective, baking powder can be used in any recipe to leaven it. Baking powder contains baking soda combined with an acid. This means that when baking powder is hydrated it will immediately begin reacting because the acidic component is already present. You can read more about how baking soda and baking powder function in baking here. 


Yeast is a type of biological leavening because it is a living organism- a fungus! Yeast eats sugars and starches present in dough and produces carbon dioxide and alcohol. This process is called fermentation and is what makes yeast dough rise.

Gif of yeast working to leaven a bread dough
Yeast working to leaven a bread dough (fermentation)

Yeast produces carbon dioxide slowly which means the surrounding dough must be very elastic so it can contain the gasses for a long period of time. This is why yeast dough is kneaded to develop the gluten structure. This is why yeast is not typically used for dough and batters with a weak structure. Learn more about how yeast works in baking here. 


Stiff peaked meringue

Air is a type of physical leavening that is used frequently in baking. The most common instance of air leavening our baked goods is by creaming together butter and sugar. This process of beating solid fat and sugar together forces air to get trapped in a web of sugar and fat adding volume to the baked good.

Air is also used when whipping egg whites or cream. This process also traps little pockets of air in the substance which lighten and leavens.


Steam is another powerful type of physical leavening. Certain ingredients such as butter, eggs, and milk contain water which will evaporate in the oven, creating steam. While this may not sound as exciting as the chemical and biological reactions of other leavening agents, when water evaporates it increases in volume by 1500 times. Steam can create a great deal of volume in a baked good.

Pinwheel shaped danish using puff pastry

One of the most evident examples of steam leavening a baked good is with puff pastry. Puff pastry is made up of many layers of alternating dough and butter. When the water present in the butter evaporates in the oven, the steam causes the dough to puff up tremendously. Steam is the only leavening agent doing all the work in this incredibly puffy pastry.

Choux pastry is another example of a baked good leavened using only steam. The evaporation from all of the liquid present in choux pastry is what makes cream puff and profiterole shells completely hallow in the middle.

Homework for this Lesson

As always, the homework is optional but is a good way to practice. Now that you understand all of the different types of leavening and how they function in baking, I want you to try your hand at making something with choux pastry. Choux pastry is an incredibly example of how powerful steam can be to leaven our baked goods. It is also a baking staple that can be used to make so many different kinds of pastries.

You can find the tutorial for how to make choux pastry here, and then this batter can be used to make a variety of things listed below. If this is your first time making choux pastry, I think you will be surprised and how much volume is gained just from the steam!


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