Chemical Leaveners – Agent de Levage
Leavening with yeast is considered to be a biological process because it exploits the function of living organisms to produce the desired carbon dioxide gas. This same gas can be produced using a combination of faster-acting chemicals as well. While the origins of chemical leaveners are somewhat obscure, it is known that American colonists in the 18th century were using leavening agents made from a by-product of wood ash. Baking soda (sodium bicarbonate) and then baking powders (a combination of sodium bicarbonate and a leavening acid, such as cream of tartar) were subsequently developed and introduced onto the market. Apart from baking ammonia, which is seldom used, chemical leaveners involve a reaction that occurs when the alkaline sodium bicarbonate reacts with an acid to produce carbon dioxide gas that inflates a batter or dough. The reason chemical leaveners are used in place of yeast is that batters for cakes and quick breads are more liquid and do not have the developed gluten content of bread dough. This means that the batter does not have the structural ability to hold the carbon dioxide for the length of time it takes yeast to ferment. Because chemical leaveners are set off by moisture and heat, the batter rises while it is being cooked. In this way the proteins in the batter firm up just in time for the leavener to stop producing carbon dioxide gas.
Baking Soda – Bicarbonate de Sodium
Baking soda (sodium bicarbonate) is a white powder that reacts with acidic ingredients in a dough or batter to produce carbon dioxide that causes dough to rise. Quick-bread recipes that use only baking soda require acidic ingredients such as buttermilk, yogurt, various fruit juices, and even molasses and brown sugar to cause the necessary chemical reaction.
Baking Powder – Levure Chemique
Baking powder is a mixture of sodium bicarbonate (baking soda) and watersoluble acid crystals that are packed together in a protective starch medium the starch simply keeps the acid and alkaline ingredients from interacting.
When this mixture comes into contact with a liquid, the sodium bicarbonateand the acid crystals dissolve and interact. This causes a chemical reaction that produces carbon dioxide gas that leavens the batter. Different acid crystals can be used in baking powder, and each type comes with its own strengths and weaknesses. Cream of tartar, for instance, reacts with sodium bicarbonate at a low temperature. For this reason, preparations with this acid component must be cooked soon after mixing; otherwise the batter may rise and fall before it is finished cooking. The benefit of cream of tartar is that it leaves little or no aftertaste.
By contrast, sodium aluminum sulphate (SAS) reacts with sodium bicarbonate at higher temperatures which means the batter can sit for a while before being cooked. The downside is that SAS can leave an aftertaste, and, though it is used in such small quantities, its presence raises some health concerns. Double-acting baking powder contains a combination of both hightemperature and low-temperature acid crystals.
Source : Mastering the Art and Craft : Baking & Pastry The Culinary Institute of America 2nd edition
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