The leavening acid, sodium acid pyrophosphate (SAPP) is an important component of double acting baking powder as well as self rising flour. SAPP reacts in stages and is desirable in baking applications for its slow action.
Properties of Sodium Acid Pyrophosphate:1
Chemical formula: Na2H2P2O7
Molecular Weight: 221.94
White crystalline powder or granules
Soluble in water
Initially, when moisture is added to form a dough, SAPP reacts with baking soda (sodium bicarbonate) to produce carbon dioxide gas. In fact, 22-40% of gas is released during this initial two minute mix. The remaining gas, over 50%, is released when heat is applied during the baking process.2
Because SAPP is slow acting and does not react quickly with baking soda, it is the most commonly used leavening acid for self rising flour for the home baker. Per 21 C.F.R. § 137.180(a) 2018, self rising flour must contain enough leavening acid to neutralize the baking soda, but the combination of both can not exceed 4.5 parts per 100 parts flour.
The quantity of leavening acid needed hinges on its neutralizing value (NV) which is defined as the quantity of baking soda needed to neutralize 100 parts of leavening acid. For SAPP, NV is 70.
Because SAPP can have a slight bitter taste, it’s important to use sufficient baking soda in applications as well as use this leavening acid in combination with sugary goods such as doughnuts and cakes. Cake doughnuts are an important application for SAPP, where initial gas production is necessary for buoyancy in a fryer system. Also, SAPP is useful for cakes, where initial gas production is necessary for consistency of pan fill.
Other non-bakery food applications of SAPP include use as a chelating agent for processed potatoes, an emulsifying agent in cheeses and a curing accelerator in processed meats.