Chemical leaveners are important ingredients used in cookie and cracker products that cause expansion to occur by releasing carbon dioxide (CO2) gas into air cells established in the dough during mixing. The most common chemical leaveners used are ammonium bicarbonate or a combination of sodium bicarbonate with one or more acids. Ammonium bicarbonate, in the presence of moisture, requires only heat to react and provide expansion. Sodium bicarbonate (commonly called baking soda, or simply soda) requires an acid to produce CO2 gas. Some chemical leaveners will react during mixing, while others work during the baking process. All impact critical quality measures of your finished product including grain, texture, spread, height, surface appearance, color, and flavor.
- Grain: refers to the internal geometry of the product, including the shape, uniformity, size of the air cells, as well as the cell wall thickness. These air cells are established during mixing, and the grain is largely determined by their number and size. The larger the number and the smaller the size of air cells produced during mixing, the more fine and uniform the grain. The leaveners we use will expand within those air cells, also called nucleation sites. Using baking soda alone will react with the natural acidity of your other ingredients and begin to react in the mixer, contributing to an increase in nucleation sites. This process is enhanced by the addition of a fast acting acid such as MCP (Monocalcium phosphate) that will cause more of the soda to react early in the process. The use of slow acting leaveners, such as SAPP (sodium acid pyrophosphate) will only have some reaction during mixing, and delay the full reaction of the soda until heat is applied during the baking process. Ammonium bicarbonate, on the other hand, will not contribute significantly to gas production until baking. As you increase the quantity and type of leaveners that contribute to expansion during mixing, the grain will become more fine and uniform.
2. Texture: the hardness or tenderness of a product. There are many ingredients that will contribute significantly to texture, including the type of flour and the type and quantity of fats and sugars used. The leavener’s contribution is tied to its influence on the grain described above. Generally, products that are more open will be more tender, and products that are more dense will be harder. Very lean formulas, those with low levels of fat and sugar, can be made more tender by increasing the leavening and opening up the grain, giving a less dense, more tender texture. Other, more rich formulas have more varied options for creating tenderness with adjustments to fats, flours, and sugars.
3. Volume: While most cookies and crackers don’t rise much during baking, height is still a critical measurement, as is spread for cookies in particular. Height in crackers is achieved largely through steam expansion during baking, but this is enhanced through the use of chemical leaveners. Spread is extremely important for the finished cookie characteristics as well as for packaging concerns. The chemical leaveners you choose will have a greater influence on spread than they do on height in most cookies, and because many types of cookies will collapse or settle to some extent as they cool, height is often controlled indirectly by controlling spread. As you increase the leavening in cookies, both the spread and height will increase, although to a varying degree depending on the leavener you choose. Additionally, there are many other ingredient and process considerations that will determine whether or not you are able to maintain the height you achieve during baking.
4. Surface Cracks: The surface appearance is often the first thing a customer will notice about the product. Many cookies have a smooth surface, but in other products a cracked surface is desired to give a more rustic or homemade appearance, as with some varieties of wire cut cookies. These cracks are formed when the moist interior continues to produce steam and expand after the surface has dried set during the beginning of the baking process. Increase in the occurrence and size of surface cracks can be influenced by an increase in total quantity of leavener, choosing slower acting leaveners, and adjusting bake settings in the first zones of the oven.
5. Color and Flavor: Another major factor that your customers will notice immediately, and is view as important to the perception of quality is color and flavor. Both elements are impacted by the level of browning that occurs during baking. The reactions that cause color and flavor generation during baking, caramelization and the Maillard Browning Reaction, are influenced by pH. Both are accelerated at a higher (more alkaline) pH and slowed at a lower (more acidic) pH. An increase in the quantity of soda (an alkaline ingredient) will increase the product pH, causing a darker color and a more alkaline flavor in the finished product, since not all of the soda added is neutralized during baking. Some of the soda is neutralized due to the acidic nature of other ingredients (flour and liquid sugars, for example), and more yet may be neutralized by the addition of MCP or SAPP to further react the soda.
These adjustments in your formula will determine how much of the soda remains during baking and in the finished product. Ammonium bicarbonate, the other primary chemical leavener, is also an alkaline ingredient. However, when properly handled and balanced in your formula, all of the ammonium bicarbonate is baked out, leaving no residual in the product. (This is, in fact, critical, as the ammonium bicarbonate is caustic and has an extremely unpleasant aroma that would render the product inedible if any residual remained). So, in this case, the browning reactions are still accelerated during baking while the ammonium bicarbonate is present, but the finished product pH is not affected since there is no residual left after baking.
Leavening choices can achieve a wide range of results that will affect the customer’s first and lasting impression of your products. It is important to understand the influence of your ingredient functionality and interactions whether you are developing new products or troubleshooting your current products.