Technical Talk: Oct 06

Chemical Leavening

This column is written by Dr. John Michaelides of the Guelph Food Technology Centre.

Question: What are chemical leavening agents, what are the different types, and how are they used in baked goods?

Answer: The process of making many different types of baked goods requires the aeration of the dough or the batter. This is achieved by the action of the leavening agents. The process of aeration makes the structure of the dough and batter light and fairly porous, which translates into the crumb characteristics of the finished baked products. In the process of baking, the porosity of the batter is very important because it results in good volume and provides tenderness and good cell structure in the crumb.

The leavening in baked goods is achieved by the production of carbon dioxide, either from the action of yeast through the fermentation process, or by the release of carbon dioxide through the reaction of different chemical leavening agents. Leavening can also be achieved by the mechanical aeration of mixing and creaming of batters, and the water vapour that forms by the heat of baking.

In the last issue, we discussed how yeast is used as leavening agent for different yeast-raised baked goods. In this issue, we will discuss the different types of chemical leavening agents available and their role in the multitude of baked goods you make.

The most common chemical leavening agents used in cake products consists of the combination of sodium bicarbonate (or, as it is commonly called, baking soda) and various acidic agents. Sodium bicarbonate is the most commonly used source of carbon dioxide because it is relatively cheap, it is non-toxic, and it is easy to handle. When the combined mixture of sodium bicarbonate and different acids is brought into contact with water, they react to produce carbon dioxide at controlled levels and rates which are dependent on the type of acidic agents in the mixture. The different leavening acids are available for bakers to combine with baking soda and use in their formulations.

In addition, premixed baking powders are also available which are more convenient, but are restricted in their application. There are three basic types of baking powders: fast-acting, slow-acting and double-acting. The fast-acting powders release most of the carbon dioxide in a few minutes after coming into contact with water. For this reason a very quick processing of the batter is required in order to avoid loss of volume. The slow-acting baking powders, on the other hand, do not release any carbon dioxide until they are exposed to the heat of the baking. Double-acting baking powders react partially at low temperatures, releasing some carbon dioxide, and complete the reaction during the exposure to the baking temperatures. Double-acting baking powders are the most commonly used for commercial cake baking because they perform a uniform, regulated action, resulting in good cake characteristics.

Baking powders contain the same reactive compounds of baking soda and the particular leavening acids, but also contain other inert compounds, such as cornstarch, calcium carbonate, calcium sulfate, calcium lactate, etc. These inert compounds serve to keep the reactive compound apart in order to prevent premature reaction and to standardize the powder strength. It is important that these inert compounds contain very low moisture but also consist of a specific particle size in order to achieve good storage stability of the baking powder.

Another common source of carbon dioxide which can be used as a leavening agent is ammonium bicarbonate. When ammonium bicarbonate is heated it releases carbon dioxide and ammonia. Its use, however, is restricted to some dry cookies and crackers because in any products that contain moisture the ammonia will be retained and the baked goods will be inedible.

As I mentioned earlier, the baker or the baked goods formulator has the choice to use a complete premixed system of baking powder which is commercially available or combine sodium bicarbonate with various leavening acids. There are currently eight different leavening acids to choose from depending on the application required. These are:

1. Anhydrous monocalcium phosphate (AMCP), a very stable ingredient protected from ambient moisture by a coating of potassium and aluminum phosphates. It is fairly slow reacting, with only about 15 per cent of carbon dioxide released at the mixing stage.

2. Dicalcium phosphate dehydrate (DCP) has a very slow reactive rate and only reacts with sodium bicarbonate when the temperature of the batter reaches 60 C.

3. Glucono-delta-lactone (GDL) reacts slowly to release gluconic acid, which in turn reacts with sodium bicarbonate to release carbon dioxide. It may leave a bitter aftertaste in the product but is suggested to reduce fat absorption in donuts.

4. Monocalcium phosphate (MCP), a very fast reacting leavening acid which releases most carbon dioxide (60 to 70 per cent) by the end of the mixing stage with the remainder being released during baking. Its action results in batters with high viscosity and high volume.

5. Potassium acid tartrate (cream of tartar) is one of the fastest reacting leavening acids with about 70 per cent released within the first two minutes. For this reason, its use is very limited.

6. Sodium acid pyrophosphate (SAPP), which comes in different grades with different reaction rates form very slow to slow. Very slow SAPP grades are used in cake donuts because they require partial leavening action during the frying period in order to achieve buoyancy without full expansion. Cake donuts usually require a number of different fast and slow reacting acids. The slow acting grades of SAPPs are also used in canned refrigerated biscuit doughs.

7. Sodium aluminum phosphate (SALP) is one of the most commonly used leavening acids in double-acting systems. It releases carbon dioxide quickly during the baking stage, does not contribute to flavour changes, and does provide strong fine close texture with the added benefit of reducing tunnel formation in cakes.

8. Sodium aluminum sulfate (SAS) is a very slow-acting acid with practically no reaction at room temperature. It was used in combination with other fast leavening acids to produce the first double acting baking powder. SAS is used in special applications such as chocolate cake, where it contributes to a characteristic colour, and in English muffins, where it is responsible for the large gas holes due to the quick release of the carbon dioxide when the English muffins are heated on a grill.

This is a quick attempt to introduce to you the various chemical leavening agents and provide you with some options. Suppliers of leavening agents and leavening acids can provide a more complete list of their available ingredients that can help you with formulations of your products.

For more information, or fee for service help with product or process development needs, please contact the GFTC at (519) 821 1246, by fax at (519) 836 1281, by e-mail at gftc@gftc.ca.