Figure 1. The rate of reaction of various leavening acids as a function of temperature. The width of the triangles indicates the rate of reaction. MCP is the fastest-acting acid, while DCP.Di is the slowest leavening acid. Source: Ref. 9 (data for MGP from B. Heidolph, personal communication).

though the basic molecule is the same in all cases, Ca+ + slows the dissolution rate of SAPP granules. Thus the inclusion of milk in a SAPP-leavened formulation (eg, a pancake batter) delays the time of leavening slightly. The various reaction grades are made by intentionally adding a certain amount of Ca+ + to the disodium salt during manufacture (adjustments in granule size also control dissolution rate). The grade designations used by Monsanto Chemical Co. range from SAPP-43 (the fastest) through 40, 37, and 28 to 21 (formerly called SAPP RD-1, the slowest). The corresponding grades marketed by Stauffer Chemical Co. (now a division of Rhone-Poulenc) are named Perfection, Donut Pyro, Victor Cream, BP Pyro, and SAPP #4. The slowest grade is used in making refrigerated biscuits and doughs, whereas for other uses (cakes, cake doughnuts, biscuits, and pancakes) a combination of SAPP acids is used to get continuous leavening throughout the baking cycle.

The high reaction rate of MCP may be moderated by coating it with a somewhat insoluble material. This coating dissolves slowly with time, allowing the MCP to then dissolve and form H+. Instead of 70% of the reaction occurring during the first 10 min after mixing, coated MCP typically gives 20% reaction immediately and then the other 50% over the next 30 min.

The slow-reacting SAIP and DMP leavening acids are useful in pancake and waffle batter for restaurant use, where little or no evolution of C02 is desired during the holding period between uses.

Formula Balance. Some of the ions found in leavening acids may influence other properties of certain baked goods. The pyrophosphate ion gives a certain taste that is detectable by some people. Aluminum ion plays a role in developing optimum layer cake structure (15), and SAIP and/or SAS is useful as part of the leavening system. So dium aluminum sulfate is reported to contribute to rancidity in dry cake mixes stored for a long time. Calcium ion also helps set protein structure and contributes to fine grain in cakes and cake doughnuts. One leavening acid may be selected over another with an equivalent reaction rate just to take advantage of these ion effects.

Developing a formulation with a properly balanced chemical leavening system is partly science and partly art—preplanning followed by trial and adjustment. The selection of timing of the leavening acids, the ratio between the various ones that might be used, the total amount of C02 required, and the amount of excess of sodium bicarbonate desired are all factors that interplay with other ingredients and structural functionalities in the baked goods. Achieving the correct leavening balance in a particular formula requires a certain amount of trial and error.

Baking Powder

In the latter part of the nineteenth century, baking powders were developed that combined both parts of the chemical leavening system—baking soda and a leavening acid. The first baking powder contained only one leavening acid, anhydrous MCP, and reacted fairly quickly in cake batters, biscuits, and so on. Soon afterward, sodium aluminum sulfate was incorporated; this gives leavening action during the middle of the baking process, in addition to the early action due to the MCP. This double-acting baking powder was a great success. In Table 3 some typical compositions of baking powders are shown. In addition to the soda and acid, various fillers and calcium salts are also included. The level of potential leavening gas is nearly constant: it is the amount of C02 equivalent to 28% sodium bicarbonate in the single-acting powder, and carbon dioxide equivalent to 30% soda in all the double-acting types. Thus these powders are interchangeable from the standpoint of the amount of leavening achieved during baking.

Table 3. Baking Powder Compositions

Double-acting types

Table 3. Baking Powder Compositions

Double-acting types

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