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Baking powder

Dry chemical leavening agent

  • 20 min read
  • 6 chapters
Baking powder, showing a 2013 container and the powder itself. Labeled aluminum-free, gluten free, double acting, non-GMO, rumfordworld.com. Ingredients: monocalcium phosphate, sodium bicarbonate, cor
Lou Sander · CC BY-SA 3.0

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Through Acid, Carbon dioxide and Acid–base reaction

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 desiccants 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

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)

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