Raising Agent

A raising agent (also called leavening or leaven) is a substance used in doughs and batters that causes a foaming action intended to lighten and soften the finished product.

The function of the raising agent is to puff up the food that it spreads and rises and becomes full of holes, thus making it light and not close and heavy. The holes made by the raising agents are retained during the process of cooking. The leavening of the flour mixture is accomplished by the expansion of water vapour and carbon dioxide. When the product is heated the air expands and part of the water vaporizes. The formation of carbon-dioxide requires the presence of suitable microorganisms or chemical agents. During the

first part of heating gas production is accelerated and the gas formed expands as the temperature rises.

The following are the different types of raising agents:

· Biological raising agents

· Chemical raising agents

· Mechanical leavening

· Other leaveners

Biological Leaveners

Microorganisms that release carbon dioxide as part of their lifecycle can be used to leaven products. Varieties of yeast are most often used, particularly Saccharomyces species (i.e. baker's yeast), though some recipes also rely on certain bacteria. Yeast leaves

behind waste byproducts (particularly ethanol and some autolysis products) that contribute to the distinctive flavor of yeast breads. In sourdough breads, the flavor is further enhanced by various lactic or acetic acid bacteria. Leavening with yeast is a process based on fermentation, physically changing the chemistry of the dough or batter as the yeast works. Unlike chemical leavening, which usually activates as soon as the water combines the acid and base chemicals, yeast leavening requires proofing, which allows the yeast time to reproduce and consume carbohydrates in the flour.

While not as widely used, bacterial fermentation is sometimes used, occasionally providing a drastically changed flavor profile from yeast fermentation; salt rising bread, which uses a culture of the Clostridium perfringens bacterium, is a well-known example.

Some typical biological leaveners are:

§ beer (unpasteurised - live yeast)

§ buttermilk

§ ginger beer

§ sourdough starter

§ yeast

§ yogurt

Chemical Leaveners

Chemical leaveners are chemical mixtures or compounds that typically release carbon dioxide or other gases when they react with moisture and heat; they are almost always based on a combination of acid (usually a low molecular weight organic acid) and an alkali (though ammonia-based leaveners are also available, though in decreasing quantity). They usually leave behind a chemical salt. Chemical leaveners are used in quick breads and

cakes, as well as cookies and numerous other applications where a long biological fermentation is impractical or undesirable. Since the chemical expertise required to create a functional chemical leaven without leaving behind off-flavors from the chemical precursors involved, such substances are often mixed into premeasured combinations for maximum results. These are generally referred to as baking powders.

Chemical leavening agents include:

§ baking powder

§ baking soda (sodium bicarbonate)

§ ammonium bicarbonate (hartshorn, horn salt, bakers

ammonia)

§ potassium bicarbonate (potash)

§ potassium bitartrate (cream of tartar)

§ potassium carbonate (pearlash)

§ monocalcium phosphate

Mechanical Leavening

Mechanical leavening is the process of incorporating air by whisking, beating and sieving. Creaming is the process of beating sugar crystals and solid fat (typically butter) together in a mixer. This integrates tiny air bubbles into the mixture, since the sugar crystals physically cut through the structure of the fat. Creamed mixtures are usually further leavened by a chemical leavener. This is often used in cookies.

Using a whisk on certain liquids, notably cream or egg whites, can also create foams through mechanical action. This is the method employed in the making of sponge cakes, where an egg protein matrix produced by vigorous whipping provides almost all the structure of the finished product.

Other Leaveners

Steam and air are used as leavening agents when they expand upon heating. To take advantage of this style of leavening, the baking must be done at high enough temperatures to flash the water to steam, with a batter that is capable of holding the steam in until set.

Air as a Raising Agent:

Air is incorporated by sifting flour, by creaming shortening, by beating eggs or by beating the mixture itself.

Water Vapour as a Raising Agent:

Water vapour is formed in quantities sufficient to raise the mixture when liquid and flour are in equal volumes.