There are several types of leavening agents that aid in the bread rising process: yeast, natural leavens and chemical leavens.
Yeast is an essential ingredient that makes the dough rise and gives home-baked yeast bread its wonderful taste and aroma. Other ingredients are added to complete the reactions that result in a perfectly baked loaf of hot, crusty homemade bread. When activated by warm liquid, and fed by sugar or starch, the yeast releases tiny bubbles of carbon dioxide gas. This gas is what makes the dough rise and achieve its light texture after baking.1
Yeast is available in four different forms: active dry yeast, quick-rise yeast, bread machine yeast and compressed fresh cake yeast. All types of yeast are interchangeable.
Active dry yeast - The original dry yeast was introduced in 1943. It works best when dissolved in water prior to mixing. It is manufactured by Fleischmann's, Red Star and SAF and sold in dated 1/4-ounce flat packets, in three-packet strips, 4-ounce jars, or in bulk at natural food stores. One scant tablespoon of dry yeast is equal to a 1/4-ounce pre measured package or a 6-once cube of fresh cake yeast. Keep dry yeast stored in the refrigerator in a tightly covered container. If it is unopened, it will remain active for up to a year. If it has been opened, it should be used within 3 months for optimum use.
Quick-rise yeast - This type of yeast was developed in 1984 and is manufactured by Red Star and Fleischmann's (RapidRise™). You do not need to dissolve it first, you can combine it with other ingredients when you use the quick, one-rise method. Since only one rise is required, the time it takes for dough to rise is significantly shortened...by as much as 50%. Follow the manufacturer's instructions, as dough temperature and rising times are different than for general bread making. This yeast is available in 1/4-ounce packages and sold in a three-package strip.
Bread machine yeast - Bread machine yeast is the latest member of the yeast family and was developed to meet the demands of electronically oriented home bakers. It is fast-acting and reduces rising time by as much as 50% by eliminating the first rise. It is designed for mixing directly with other dry ingredients before use and can be used interchangeably with active dry yeast, fast-acting, and quick-rise yeasts. It is manufactured by Fleischmann's, SAF and Red Star and is available in a 4 oz. glass jar.
Compressed fresh cake yeast - This type of yeast comes in a cake form. To use, simply crumble into dry ingredients or soften in warm water first. This type of yeast is known for its dependability and excellent rising ability. It is favored by artisan bakers. Fresh yeast is highly perishable and must be refrigerated; it will keep for about 2 weeks. Fresh yeast should be dissolved in tepid liquids before being added to the dry ingredients. A 6-ounce cake of fresh yeast is equal to a 1/4-ounce package of active dry yeast. It is manufactured by Fleischmann's and Red Star and is sold in 6-ounce and 2-ounce cakes and 1-pound blocks.
Breads can also be made with natural leavening agents. It is thought that since the early days, leavening mixtures for bread making were formed by natural contaminants in flour such as wild yeast and lactobacilli, organisms also present in milk.2 Breads made with natural leavens such as a Sourdough Starter have a different flavor and texture from breads made with commercial (fresh or dry) yeast.
You can use leavening agents other than yeast to make breads. These chemical leavens - baking soda, baking powder and cream of tartar - are most commonly used for tea breads or quick breads that are mixed in a bowl, then baked in a bread pan.
Baking Soda alias sodium bicarbonate, is a naturally occurring substance that is found in all living things, where it helps regulate their pH balance. It is an alkaline raising agent that is often used for quick breads. When you moisten baking soda with liquid, it gives off carbon dioxide which makes the quick bread rise.
Cream of Tartar is a by-product of the wine industry. It is an acid which is often combined with baking soda to boost the baking soda's leavening ability. It also helps to neutralize the slightly soapy taste of the baking soda.
Baking Powder is a ready-made mixture of acid and alkaline chemicals, usually baking soda and cream of tartar. You can make your own baking powder if you have baking soda and cream of tartar. Simply mix two parts cream of tartar with one part baking soda.
Tip: All of the chemical leavening agents are fast acting. The reaction begins immediately upon mixing the dry ingredients with liquid, so you need to mix and bake these recipes immediately, or else they will collapse.
1© 1996-2007 ACH Food Companies, Inc. All rights reserved.
2© 2008 Lesaffre Yeast Corporation All rights reserved.
© 2008 Church & Dwight Co., Inc. All Rights Reserved.
Helmenstine, Ph.D., Anne Marie. "What is the Difference Between Baking Soda & Baking Powder?" About.com
Hensperger, Beth. Bread Made Easy: A Baker's First Bread Book. Copyright 2000. Ten Speed Press.
Shapter, Jennie. Bread Machine - How to prepare and bake the perfect loaf. Hermes House 2003.