Baking powder is a dry chemical leavening agent, a mixture of a carbonate or bicarbonate and a weak acid. The base and acid are prevented from reacting prematurely by the inclusion of a desiccant such as cornstarch. Baking powder is used to increase the volume and lighten the texture of baked goods. It works by releasing carbon dioxide gas into a batter or dough through an acid–base reaction, causing bubbles in the wet mixture to expand and thus leavening the mixture.
The first commercially sold baking powder ever was Borwick's Baking Powder, launched in England in 1842 by George Borwick, who had spent eleven years from 1831 perfecting a formula passed to him by his father-in-law, a chemist, as a yeast substitute for home baking. The following year, in 1843, pharmacist Alfred Bird developed his own single-acting baking powder (meaning that it releases all of its carbon dioxide as soon as it is dampened). In 1856, Eben Norton Horsford, the Rumford Professor at Harvard University, received an American patent, for monocalcium phosphate, for baking powder. In the 1860s, Horsford developed the first double-acting baking powder, which releases some carbon dioxide when dampened and later releases more of the gas when heated by baking
Baking powder is used instead of yeast for end-products where fermentation flavors would be undesirable, or where the batter lacks the elastic structure to hold gas bubbles for more than a few minutes, and to speed the production of baked goods. Because carbon dioxide is released at a faster rate through the acid–base reaction than through fermentation, breads made by chemical leavening are called quick breads. The introduction of baking powder was revolutionary in minimizing the time and labor required to make breadstuffs. It led to the creation of new types of cakes, cookies, biscuits, and other baked goods.
Formulation and mechanism Baking powder is made up of a base, an acid, and a desiccant to prevent the acid and base from reacting before their intended use. Most commercially available baking powders are made up of sodium bicarbonate (NaHCO3, also known as baking soda or bicarbonate of soda) and one or more acid salts.
Acid-base reactions When combined with water, the sodium bicarbonate and acid salts react to produce gaseous carbon dioxide. Whether commercially or domestically prepared, the principles behind baking powder formulations remain the same. The acid-base reaction can be generically represented as shown:
NaHCO3 + H+ → Na+ + CO2 + H2O
The real reactions are more complicated because the acids are complicated. For example, starting with baking soda and monocalcium phosphate, the reaction produces carbon dioxide by the following stoichiometry:
14 NaHCO3 + 5 Ca(H2PO4)2 → 14 CO2 + Ca5(PO4)3OH + 7 Na2HPO4 + 13 H2O
A typical formulation (by weight) could call for 30% sodium bicarbonate, 5–12% monocalcium phosphate, and 21–26% sodium aluminium sulfate. Alternately, a commercial baking powder might use sodium acid pyrophosphate as one of the two acidic components instead of sodium aluminium sulfate. Another typical acid in such formulations is cream of tartar (KC4H5O6), a derivative of tartaric acid.
Double-acting baking powders The use of two acidic components is the basis of the term "double acting". The acid in a baking powder can be either fast-acting or slow-acting. A fast-acting acid reacts in a wet mixture with baking soda at room temperature, and a slow-acting acid does not react until heated. When the chemical reactions in baking powders involve both fast- and slow-acting acids, they are known as "double-acting"; those that contain only one acid are "single-acting".
By providing a second rise in the oven, double-acting baking powders increase the reliability of baked goods by rendering the time elapsed between mixing and baking less critical. This is the type of baking powder most widely available to consumers today. Double-acting baking powders work in two phases; once when cold, and once when hot.
Thus, a double-acting baking powder, with baking soda, uses fast-acting acid that reacts in a cool (room temperature), wet mixture. Later, after heating, the slower-acting acid reacts, with baking soda, in the wet mixture, at the now-high-temperature. Slower-acting acids only react at higher than room temperatures.
However, Rumford Baking Powder is a double-acting product that contains only one leavening acid, monocalcium phosphate. With this acid, about two-thirds of the available gas is released within about two minutes of mixing at room temperature. It then becomes dormant because an intermediate species, dicalcium phosphate, is generated during the initial mixing. A further release of gas requires the batter to be heated above 140 °F (60 °C).
Common low-temperature acid salts include cream of tartar and monocalcium phosphate (also called calcium acid phosphate). High-temperature acid salts include sodium aluminium sulfate, sodium aluminium phosphate, and sodium acid pyrophosphate.
Starch component Baking powders also include components to improve their stability and consistency. Cornstarch, flour, or potato starch are often used as desiccantsJohn Brodie, John Godber "Bakery Processes, Chemical Leavening Agents" in Kirk-Othmer Encyclopedia of Chemical Technology 2001, John Wiley & Sons. An inert starch serves several functions in baking powder. Primarily it is used to absorb moisture, and so prolong shelf life of the compound by keeping the powder's alkaline and acidic components dry so as not to react with each other prematurely. A dry powder also flows and mixes more easily. Finally, the added bulk allows for more accurate measurements.
Commonly used bases and acids Baking powder is made of two main components: an acid and a bicarbonate base. When they are hydrated, an acid–base reaction occurs, releasing carbon dioxide. Commonly used acids and bases for baking powders are:
Bases
Sodium bicarbonate Ammonium bicarbonate Potassium bicarbonate
Acids Dicalcium phosphate dihydrate (DCPD) 33 neutralizing value Glucono delta-lactone (GDL) 45 neutralizing value Fumaric acid Dimagnesium phosphate (DMP) Anhydrous monocalcium phosphate (AMCP) 83 neutralizing value Acids, Low-temperature Potassium acid tartrate (cream of tartar) 45 neutralizing value Monocalcium phosphate (MCP) 80 neutralizing value Acids, High-temperature Sodium acid pyrophosphate (SAPP) 72 neutralizing value Sodium aluminium phosphate (SALP) 100 neutralizing value Sodium aluminium sulfate (SAS) 104 neutralizing value
Neutralizing value The neutralizing value (NV) is defined as the amount of baking soda required to neutralize 100 parts of a leavening acid (by weight).
Neutralizing value can be expressed through the following formula:
NV = g of NaHCO3 neutralized by 100 g leavening acid
Rate of reaction The rate of reaction (ROR) is represented by the percentage of carbon dioxide released by the acid-base reaction.
Other subcategories exist to classify the reaction rated during mixing and holding called “Dough Reaction Rate (DRR)” and during baking at a given temperature denominated “Batter Reaction Rate (BRR)”.
The ROR of baking powders is impacted by many factors, including:
Acid type: moisture and/or heat reactivity are influenced by its physicochemical properties, such as solubility and dissociation extent. Granulometry Temperature of dough or batter Concentration of leavening acid and base Hydration Presence of water-binding ingredients (e.g. sugars, alcohols, starches, gums, salt) Presence of cations (calcium)
History
Before baking powder When Amelia Simmons published American Cookery (1792), the first American cookbook, three known types of leavening were used in its recipes: baker's yeast, emptins (from the leavings of brewer's yeast), and pearlash. At that time, the mechanisms underlying the action of yeasts and other leavenings were not understood, and reliable commercial products were not available. Bakers obtained yeasts from brewers or distillers or made their own by exposing mixtures of flour and water to the open air. If lucky, they could capture useful wild yeast and keep some alive, regularly feeding it for ongoing use and trying to avoid contamination. Women who made their own ale could use the brewing dregs or "emptins" in their baking.
The effectiveness of such leavenings varied widely. Resulting baked goods often had a sour or bitter taste. Breads were made of grain, water, yeast, and sometimes salt. Cooks also made yeast, sponge and pound cakes. Yeast cakes were similar to breads but included fancier ingredients, like sugar, spices, fruits or nuts. Sponge cakes used beaten egg whites for leavening. Pound cakes combined butter, sugar, and flour and eggs, and were particularly dense. Making cakes was even more laborious than making bread: to prepare a cake, a manservant might have to beat the ingredients together as long as an hour.
Pearlash The third type of leavening, pearlash, was the precursor to modern baking powder. Pearlash was a purified form of potash. According to Joop Witteveen (1985), pearlash was used in Europe by professional bakers in the mid-seventeenth century. The Oxford English Dictionary credits the first written use of the term "pearl ash" to 1703 and the writing of Abel Boyer.
By the mid-1700s, practical treatises on the calcination of pearlash were available in both England and the United States. Pearlash was the subject of the first patent in the United States, issued in April 1790. Its preparation was time-consuming, but could be accomplished with a cast-iron kettle: it involved soaking fireplace ashes in water to make lye, and then boiling the lye to remove water and obtain "salts".
The active ingredient in pearlash was potassium carbonate (K2CO3). Combining it with an acidic ingredient like sour milk or lemon juice resulted in a chemical reaction that produced carbon dioxide. Once prepared, the white powder was much more stable than yeast. Small amounts could be used on a daily basis, rather than baking a week or two weeks' worth of bread at one time. American Cookery was the first cookbook to call for its use, but by no means the last. With pearlash, cooks were able to create new recipes for new types of cakes, cookies, and biscuits that were quicker and easier to make than yeast-based recipes.
Experimentation Between the publication of American Cookery in 1796, and the mid-1800s, cooks experimented with a variety of acids, alkalis, and mineral salts as possible chemical leaveners. Many were already available in households as medicinal, cleaning or solvent products. Smelling salts, hartshorn, and sal volatile were all ammonia inhalants, containing forms of ammonium carbonate. The term "saleratus" was applied confusingly to both potassium bicarbonate and to sodium bicarbonate (NaHCO3, what we now call baking soda). Baking soda and cream of tartar were relatively new ingredients for cooks: Soda may have been introduced to American cooking by female Irish immigrants who found work as kitchen help. Cream of tartar, also known as tartaric acid or potassium bitartrate, was a by-product of wine-making and had to be imported from France and Italy.
In 1846, the first edition of Catherine Beecher's cookbook Domestic Recipe Book (1846) included a recipe for an early prototype of baking powder biscuits that used both baking soda and cream of tartar. Several recipes in the cookbook compiled by Elizabeth Hall Practical American Cookery (1856) used baking soda and cream of tartar to form new types of dough. There were recipes for a "crust" similar to modern dumplings or cobbler, several for cakes, and one for "soda doughnuts". When the third edition of Miss Beecher's Domestic Receipt Book appeared in 1858, it included 8 types of leaveners, only two of which could be made at home.