Here it is to distinguishing between non chemical and chemical leaveners.
A nonchemical source of leavening is Air.
During creaming of shortening and sugar Air is incorporated into the dough.
The amount is depending on
sugar particle size;
temperature and mixing speed
While mixing the shortening coats the sugar particles and the shortening incorporates Air. Continued mixing beyond a certain point results in a decrease of incorporated air. Melted fat or liquid oils will not incorporate Air.
The leavening happens during the baking process by expansion. Air which is incorporated expands and contributes to the leavening.
A second non chemical source is Steam.
Steam generated during the baking process of cookie or crackers contributes to the leavening of the product. Important hereby is the timing of the release and is controlled by baking temperature.
Essential is to prevent the setting of the surface in the early stage of baking. This is controlled by the right damper setup. Dampers should be closed to create a higher moisture atmosphere in the oven. In the latter stages of baking dampers are opened to facilitate moisture removal and drying of baked product to the desired moisture level.
Sodium Bicarbonate (Soda)
Soda is used in combination with monocalcium phosphate (MCP) and sodium pyrophosphate (SAPP). Both are reacting chemically with Soda to release CO2
By using different percentage of Soda cookie characteristics can be modified, as pH, diameter, height and spread ratio.
Ammonium Bicarbonate (ABC)
If ABC breaks down, it gives two molecules, ammonia and CO2 and will leave no residual salt, therefore it will have little effect on final product pH. Varying levels of ABC has the same effect on cookie characteristics as soda but have no effect on pH.
In products that have a moisture of more than 3-5% ABC should not be used. Ammonia when released dissolves in final moisture and the product will have an ammonia flavor and odor.
Monocalcium Phosphate (MCP)
MCP is a fast acting leavening acid and reacts immediately with soda when both dissolve in dough or water batter. MCP is used to provide CO2 during mixing, due to the release of CO2 by MCP influences the grain by creating the gas cell nuclei, which later determines the final grain.
MCP is an effective tool for adjusting cookie pH and other characteristics.
Sodium Acid Pyrophosphate (SAPP)
SAPP is a slow acting leavening acid and release CO2 from soda by either time delay or when the temperature is raised by baking. SAPP will also affect pH by neutralizing soda.
Function of Leaveners
… attributes are cell wall thickness and cell size, shape and uniformity. Grain differs from texture. Leaving gas incorporate during mixing of dough have an effect on grain, particularly of cookies. If achieving the optimum out of the mixing process gas cells provide a uniform grain in the baked product. The final Grain of a cookie or cracker is largely a function of the number and size of gas cells incorporated during mixing. A rule of thumb; the larger the number and smaller the size, the finer and more uniform the Grain of the baked product.
… refers to hardness or tenderness of cookies or crackers. A tight grain will give a hard Texture, where as an open grain gives a more tender product. The possible relationship should kept in mind when adjusting leavening to achieve the desired effect. It should be also taken in consideration that there are more ways to affect Texture than through to leavening. A more tender product will achieved with increased shortening levels or reduced sugar or use of a softer flour. Rich products will require lower levels of leavening and lean, inexpensive products a higher level.
… is important from the sight of the end product qualities and proper packaging. Spread can vary from day to day due to variations in the flour supply for example.
To control Spread a number of adjustments can be used, including leavening. Spread can be adjusted by modifying the level of leavening. An increase in leavening results in greater Spread. Further to that Spread can be used by using a flour higher in protein, also sugar and shortening levels affecting Spread.
…are formed through a delayed release of leavening gas. This is due to a still molten internal dough, when the surface has already set by the heat of baking.
Most effective in controlling Surface Cracks are through adjusting soda and ABC levels.
Color and Flavor
… are effected by pH on the finished product and can be controlled by balancing or unbalancing the leavening system. A balanced systems is one where the pH is close to neutral and where the leaving acids have offset the alkalinity of soda just enough.
Still very little is to find about the technology of leavening cookies and crackers. Even if in modern times the WWW provides a lot of informations, guidelines are still missing and it remains a type of art in formulators hand.