  a leavening agent (also leavening agent or leaven agent;  or ), also known as a raising agent, is any one of a number of substances used in doughs and batters that causes a foaming action that lightens and softens. the leavening agent incorporates gas bubbles into the dough. the alternative or supplement to leavening agents is mechanical leavening by which air is incorporated by mechanical means. most leavening agents are synthetic chemical compounds, but carbon dioxide can also be produced by biological agents. when a dough or batter is mixed, the starch in the flour mixes with the water in the dough to form a matrix (often supported further by proteins like gluten or other polysaccharides like pentosans or xanthan gum), then gelatinizes and "sets"; the holes left by the gas bubbles remain. ==types of biological leavening agents== * baker's yeast * beer (unpasteurisedâlive yeast) * buttermilk * ginger beer * kefir * sourdough starter == chemical leaveners == chemical leaveners are mixtures or compounds that release gases (again, usually carbon dioxide) when they react with each other, with moisture, or with heat. most are based on a combination of acid (usually a low molecular weight organic acid) and a salt of bicarbonate (hco3-). after they act, these compounds leave behind a chemical salt. chemical leaveners are used in quick breads and cakes, as well as cookies and numerous other applications where a long biological fermentation is impractical or undesirable. ===history=== chemical leavening were publicized by amelia simmons in her american cookery, published in 1796, wherein she mentions the use of pearl ash as a leavening agent. since chemical expertise is required to create a functional chemical leaven without producing off-flavors from the chemical precursors involved, such substances are often mixed into premeasured combinations for maximum results. these are generally referred to as baking powders. sour milk and carbonates were used in the 1800s. the breakthrough in chemical leavening agents occurred in the 1930s with the introduction of monocalcium phosphates (ca(h2po4)2). other leavening agents developed include sodium aluminium sulfate (naal(so4)2Â·12h2o), disodium pyrophosphate (na2h2p2o7), and sodium aluminium phosphates (nah14al3(po4)8Â·4h2o and na3h15al2(po4)8). these compounds combine with sodium bicarbonate to give carbon dioxide in a predictable manner.john brodie, john godber "bake
Fermentation_in_food_processing Leavening_agents