Also know as Chemical Leaveners, Leavening Agents and Baking Powder
What is Chemical Leavening?
Chemical leavening is a mechanism used in the baking industry to provide volume through the release of gases to enhance the eating quality of baked goods.
Chemical leavening agents added to doughs and batters undergo various decomposition and neutralization reactions to produce carbon dioxide, water vapor and in some cases ammonia. These gases are responsible for expansion, flavor, color and other aesthetic aspects of baked products, namely crumb grain size, tenderness, etc.
Most commercially used chemical leavening systems include a combination of baking soda (sodium bicarbonate) and one or more acids or acid salts.
Chemical leavening was conceived as an alternative to yeast leavening and long sourdough preparations. Back in the 19th century, the limited knowledge of microbiology and the sensitivity of yeast cells to handling and atmospheric conditions made it difficult for bakers to consistently produce high-quality batches of bread. Further complications such as the absence of commercial refrigeration and hygiene practices made it impossible to properly maintain fresh yeast.
Modern baking soda was introduced in the 19th century where bakers had to mix it with sour milk prior to its incorporation into doughs and batters to produce carbon dioxide gas. However, this approach was unpredictable, due to challenges with estimating lactic acid content in milk. Further research and testing with a variety of compounds soon led to the development of baking powder and other ways to better control gas release in bakery products.1
How does chemical leavening work?
Chemical leavening can be achieved by producing two types of gases: CO2 and NH3. These may be released by the following methods, combined or alone:
1. Decomposition reaction of ammonium bicarbonate or ammonium carbonate in the presence of heat. Ammonium bicarbonate, for example, decomposes into ammonia, carbon dioxide and water. The reaction is as follows:2
NH4HCO3→ NH3 + CO2 + H2O
2. Reaction of an acid with a base compound. Combining a leavening acid with baking soda in the presence of moisture undergoes an exothermic reaction to produce neutral salt, water and carbon dioxide. The reaction is as follows:2
HX + NaHCO3 → NaX + H2O + CO2 X: non-metal or hydrocarbon chain
When creating a leavening reaction it is crucial to know the neutralizing value to avoid an unbalance in the formula. The neutralizing value (NV) is defined as the parts (by weight) of baking soda necessary to release all the carbon dioxide by 100 parts (by weight) of a leavening acid. For example, in the case of baking soda (sodium bicarbonate, NaHCO3), NV is expressed as:
NV = g of NaHCO3 neutralized by 100 g leavening acid
Chemical leavening is a faster than a yeast leavening approach. Certain applications such frozen pizza require a combination of chemical leaveners plus yeast to provide a secondary back-up in case the yeast fails to provide the necessary rise.
Chemical leaveners can be classified into three types. The choice of the chemical leavener type depends on the process/formulation and desired characteristics of the finished product:
- Fast-acting: systems such as sodium bicarbonate-monocalcium phosphate monohydrate react quickly during mixing, hydration and floor time standing as well.
- Slow-acting: typically use a combination of sodium bicarbonate and sodium pyrophosphate where gas evolution is triggered by high baking temperatures.
- Double-acting: consist of a mixture of sodium aluminium sulfate (SAS) and monocalcium phosphate (MCP). Typical applications of double-acting leavening include products that are baked at home such as biscuits, pancakes and waffles. In addition to their effect on gas expansion and subsequent volume building, chemical leavening affects cake’s pH, crumb texture and color.
Bases and acids used for chemical leavening in the baking industry include:3
The amount of chemical leaveners used in a bakery formulation is a function of availability of ingredients, desired volume, pH and flavor of the finished product. Bakers should always be mindful of maximum amounts permitted by the FDA.
- Smithsonian Institution. “The Great Uprising: How a Powder Revolutionized Baking.” https://www.smithsonianmag.com/science-nature/great-uprising-how-powder-revolutionized-baking-180963772/. Accessed 12 June 2018.
- Miller, R. “Leavening Agents” Encyclopedia of Food and Health, Elsevier Ltd., 2016, pp. 523–528.
- Delcour, J.A, and Hoseney, R.C. “Chemically Leavened Products” Principles of Cereal Science and Technology, 3rd edition, AACC International, Inc., 2010, pp. 177–180.