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What is Leavening?


In the first month, in the fourteenth day of the month, ye shall have the passover, a feast of seven days; unleavened bread shall be eaten. (Ezekiel 45:21)

Leaven is any agent that produces fermentation and causes dough to rise, by causing the formation of carbon dioxide gas to bubble into and spread throughout the dough. This is accomplished either chemically (as with baking soda) or biologically (as with yeast).


Leavening which has active yeast growing.

• Yeast (a single-celled fungi, used to leaven).
• Sourdough starter.

Are Leavening Agents Leaven?

Whether leavening agents by themselves (unmixed) are leaven, one must read the following and make up ones own mind.

In cooking, baking soda is primarily used in baking as a leavening agent. When it reacts with acid, carbon dioxide is released, which causes expansion of the batter and forms the characteristic texture and grain in cakes, quick breads, soda bread, and other baked and fried foods. The acid–base reaction can be generically represented as follows:

Acidic materials that induce this reaction include hydrogen phosphates, cream of tartar, lemon juice, yogurt, buttermilk, cocoa, and vinegar. Baking soda may be used together with sourdough, which is acidic, making a lighter product with a less acidic taste.

Heat can also by itself cause sodium bicarbonate to act as a raising agent in baking because of thermal decomposition, releasing carbon dioxide at temperatures above 180 °F, as follows:

When used this way on its own, without the presence of an acidic component (whether in the batter or by the use of a baking powder containing acid), only half the available CO2 is released. Additionally, in the absence of acid, thermal decomposition of sodium bicarbonate also produces sodium carbonate, which is strongly alkaline and gives the baked product a bitter, "soapy" taste and a yellow color. Since the reaction occurs slowly at room temperature, mixtures (cake batter, etc.) can be allowed to stand without rising until they are heated in the oven

• Baking Soda: a crystalline alkaline salt that gives off gas when an acid is added. 

The following are different types of baking soda:

• Sodium bicarbonate, also known as “Saleratus.”
• Potassium bicarbonate, or potash.
• Ammonium carbonate, or “baker’s ammonia.”
• Ammonium bicarbonate, also known as “hartshorn.”
• Baking Powder (baking soda + acid-forming ingredients + starch filler).

Not Leavening

* Autolyzed yeast: A yeast that has ‘self-destructed’ and is sterile – incapable of leavening.
* Brewers Yeast: A dead form of yeast that cannot leaven bread; a ‘nutritional’ yeast.
* Torula Yeast: A dead yeast that cannot leaven bread, considered a ‘nutritional’ yeast. Also hickory smoked torula yeast. Used as a savory seasoning that imparts smoky aroma to foods.
* Yeast extract(s): Derivatives of yeast, which are sterile and cannot leaven bread.
* Cream of Tartar: Tartaric acid – potassium bitartrate or potassium hydrogen tartrate. This is an acid used to combine with baking soda. By itself, this is not leavening.
* Tartrate powder: Phosphate powder or sulfate powder – usually added with cream of tartar. By itself this is not leavening.
* Alum: A metallic double salt, usually added with cream of tartar. Most common is sodium aluminum sulfate (SAS or sulfate powder), and potassium aluminum sulfate (or potash alum). By itself this is not leavening.

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