Leavening/aerating agents

Baking soda, sodium bicarbonate, "soda", NaHCO3

This compound is relatively cheap and is obtainable in various particle size grades, for example, Free Running Grade, Refined Standard Grade and Fine Granular. Each of these is suitable for baking, but coarser grades may not dissolve sufficiently quickly during the preparation and baking of a dough.

As many biscuit ingredients, including flour, have an acidic reaction it is often useful to use sodium bicarbonate as a means of adjusting the acidity of the dough and thence the taste of the resulting biscuits.

In the presence of moisture, soda will react with any acidic materials to liberate carbon dioxide gas. If the carbon dioxide liberated is required as a raising agent it is best to keep the soda away from the other ingredients for as long as possible by, for example, in multistage mixes, adding at the last stage with the flour. In these circumstances the soda powder must be evenly dispersed through the mix and if necessary the soda should be screened with a fine sieve before use to remove any lumps.

An excess of sodium bicarbonate will give biscuits with an alkaline reaction and a yellowish crumb and surface colouration with an accompanying unpleasant taste (this taste is known as soda bite).

Baking powders

Domestic baking powders are balanced mixtures of sodium bicarbonate and a crystalline acid or acid salt. When they become wet or when the dough is heated they react to liberate a gas, carbon dioxide, the bubbles of which are the basis of the open structure in a baked biscuit or cake. In the biscuit industry it is unusual to use blended baking powders and the soda and acid salt are added separately. Self raising flour has baking powder added.

Acid salts

There are several different acid salts that can be used in doughs but the most common are Acid Calcium Phosphate, (ACP) Ca(H2PO4)2.H2O and Sodium Acid Pyrophosphate, (Puron or SAPP) Na2H2P2O7. Both of these are fine white powders with an acrid acid taste. SAPP is to be preferred in biscuit doughs as the reaction with soda is very slow until the dough is heated in the oven. Much of the reaction between ACP and soda will occur in the mixer so its effect is not so good during baking because the gas bubbles produced will be squeezed out during sheeting and gauging of the dough. There are optimum ratios of soda to each of these salts but the calculations are confused because the acid salts are often sold as blends with a diluting material such as starch to make the metering easier. Refer to the suppliers’ data sheets to find out the optimum ratio of acid to sodium bicarbonate in a dough.

1.25 units of pure ACP will neutralise 1 unit of sodium bicarbonate.

1.33 units of pure SAPP will neutralise 1 unit of sodium bicarbonate.

Baking acids are always sold in multiwall paper bags and they should be stored in dry conditions.