Leavening Agent

Leavening Agents

 Give rise to flour due to:

1.     Physical agents - air & steam

2.     Biological agents - yeast & bacteria

3.     Chemical agents - baking powder & baking soda

*most of the leavening is accomplished by CO2 produced by biological/chemical sources

1.     PHYSICAL AGENTS - AIR & STEAM

• Air is incorporated during mixing. creaming of fat and sugar, by sifting dry ingredients or by whipping egg whites.
• Water from liquids added or ingredients like eggs when heated , expanding 1600 times the original volume.

2.       BIOLOGICAL AGENTS – YEAST AND BACTERIA

• Yeast (saccharomymes cerevisiae) produce CO2 through fermentation of sugars. In the absence of oxygen, yeast produce ethanol.

When hydrated and at optimum temperature (20-27˚C), yeasts that are alive but dormant become activated.fermentation is best at 27-38˚C.Yeasts feeds off the sugar in flour and added sugar.

An enzyme in yeast hydrolyzes starch to glucose and fructose, while flour amylases break down some starch to maltose, which the yeast enzyme will further hydrolyze. Forms -  fresh, dry (active), instant (fast-acting).

• Bacteria that generates CO2 are used to leaven sourdough and salt-rising breads (beside yeast). The bacteria contribute a desirable slightly sour flavour.

3.       CHEMICAL AGENTS – Baking Soda and Baking Powder

o    Baking soda yields CO2 in the presence of moisture and acid. It is often used when the flour mixture includes lemon, vinegar, buttermilk, yogurt, chocolate, cocoa, citrus fruits, cream of tartar etc. the acid reacts with the baking soda which leads to carbonic acid reaction which produces carbon dioxide and water. This immediate leavening effect necessitates the product to be placed in the oven as soon as possible after mixing.

o    Baking powder yields CO2 in the presence of moisture. Acid is already present. when liquid is added, the acid reacts with the alkaline baking powder which leads to the release of CO2.

There are two different types – fast/single acting and slow/double acting baking powder. Single acting requires the product to be placed in the oven as soon as possible after mixing as CO2 escapes, the ability of the moisture to rise increases. Double acting, on the other hand, reacts twice: once during hydration and the other one during heating.