A leavening agent is an ingredient generally added in dough or batter mixtures to help the mixture expand and rise. Once a leavening agent is added to a flour mixture, gases are released causing an expansion and therefore a lighter, fluffier and more permeable finished product. These gas bubbles are generated through a production of carbon dioxide. There are two main types of substances that can achieve this result: Biological agents & Chemical Agents. However; you can also achieve an integration/production of air bubbles through Mechanical Leavening agent as well. Here is a brief review of each:
Biological Leavening Agent: A biological leavening agent is a microscopic organism that, when fermented, releases carbon dioxide into the mixture. Fermentation of this type needs moisture, sugar and carbohydrates. Yeast is the primary Biological leavening agent used. Fermentation is a biological reaction that splits complex components into simpler substances. The science behind Yeast is relatively straightforward. Yeast works to convert the sugar into ethyl alcohol(eventually evaporates) and carbon dioxide, then the carbon dioxide causes the dough mixture to eventually rise. The fermentation stage is also referred to as the “Proofing” stage. Proofing is a slow process and gives the yeast time to reproduce and ingest carbohydrates in the flour. Warm temperature helps to speed up this process but it will still be a relatively slow process. When working with yeast, it is best to use warm water in addition to leaving it in a very warm place to rise. Out of all leavening agents, yeast delivers the leading increase in size. Fermented yeast also excretes a certain flavor into the baked product creating a unique flavor. It is best to use a biological agent such as yeast when working with mixtures that can hold in the carbon monoxide gas the fermented yeast creates. Such mixtures would include bread, focaccia, buns, rolls, etc.
Chemical Leavening Agent: A Chemical Leavening Agent is a compound created by chemicals. The two main aspects of this chemical compound are bicarbonate and acid.
- Bicarbonate: provides carbon dioxide gas.
- Acid: triggers the release of carbon dioxide from the bicarbonate immediately when introduced to moisture.
Unlike biological agents, chemical agents react almost immediately when introduced to liquid creating a quick rise to the dough/flour mixture. They are generally used in cakes, cookies, and many other quick rise type baked goods. The different types of Chemical Leavening Agents include:
Baking Soda: is a chemical compound that consists of mainly sodium bicarbonate. When heating this compound carbon dioxide as well as sodium carbonate is released. The sodium carbonate when released into the mixture creates a specific taste, odor and color that is normally not preferred in many recipes. In order for baking soda to function appropriately as a leavening agent, it must also be combined with acidic ingredients. Addition of acidic ingredients prevents the release of sodium carbonate. Such ingredients would include cream of tartar, fruits, vinegar, lemon juice, fruit juices, buttermilk, honey, etc. The ultimate chemical reaction produces carbon dioxide gas causing the batter/dough to rise.
Baking Powder: is a chemical compound that consists of Baking Soda, dry acids and fillers (normally starch) that reacts in the presence of liquid and heat. When working with Baking powder it is important to understand appropriate quantities. Too much baking powder will cause the flour mixture to stretch too far causing the flour walls to break and then collapse whereas, too little will create a compact product. Baking powder is generally used to make muffins, puddings, cakes, waffles, cookies, pancakes, etc. There are two types of Baking Powder:
- Single Acting Baking Powder: Contains cream of tartar or tartaric acid (Potassium hydrogen tartrate). They quickly release carbon dioxide when added to liquid. Such mixtures must be baked relatively quickly in order to preserve the released gas and to avoid your baked goods from falling flat. Quickly baking the mixture ensures that it retains the gas and rises as desired.
- Double Acting Baking Powder: Contains calcium acid phosphate and sodium aluminum sulfate. This type of leaven is referred to as “Double Acting” primarily because it has a 2-step rising process. It contains 2 types of acids one that reacts to cold liquid and the other reacts to heat. So, when added to a flour mixture, in the first step the baking powder is mixed with a liquid ingredient causing carbon dioxide gas to form causing the mixture to rise. But it releases only a portion of its gas during the first step and the remaining part is released during the baking process when the mixture is heated causing a further expansion.
Cream of Tartar: Is an acidic ingredient that is generally used in combination with baking soda. Cream of Tartar is a byproduct of wine-making and can also be used as a leaven. It can be used as a stabilizer in egg whites and whipped cream to increasing heat tolerance and volume. It can also be used in candies and/or sugar syrups to prevent crystallization. As discussed previously, cream of tartar in commonly used as a component in baking powder to activate the baking soda.
Ammonium Bicarbonate (Baker’s Ammonia): was used prior to Baking Soda. This can create an even lighter and extra crispier baked good but may cause a slight ammonia odor. It produces carbon dioxide as it decomposes and is best used when making crackers, gingerbread cookies, specialty cookies and certain pastries because of its texture/flavoring effects.
Other chemical leavens include Potash and Pearlash
Mechanical Leavening Agent: It is a manual process where air is incorporated into a mixture or by releasing gas already confined in the product. Creaming is a common mechanical leavening process which consists of beating sugar and solid fat such as butter in a mixer. This allows for an integration of air bubbles into the mixture creating a fluffy consistency.
Other Leavening Agents: Steam can be used as a Leavening Agent and when heated at a high temperature the dough mixture expands. Air is another leaven which is used when making a Meringue. Meringue is created by beating egg whites with an electric mixer. The protein in the mixture traps the air bubbles in the foam which creates a light and fluffy texture. Other types of foods that use mechanical leaven include angel food cakes, certain puddings, Fish Batters, etc. Nitrous oxide is another type of a Leaven. It is normally used in whipped cream cans and when released it escapes and creates a temporary foam into the fat mixture of the cream.