What is Leavening Agent?
Leavening agents are the agents that increase the surface area of the dough or batter by creating gas bubbles in the dough or batter. When the gas bubbles start to expand during baking and increase the volume of the product and give a desirable porous structure. Leavening agents are also known as Raising agents.
Table of Content
Classification of Leavening Agents
Leavening agents that are used in the kitchen can be classified into the following categories,
- Biological (yeast)
- Chemical (baking powder, baking soda, baking ammonia)
- Mechanical (beating, whisking, creaming, sieving)
- Combination of All
Biological Leavening Agents
Yeast: Yeast is a single-celled microorganism, a tiny living fungus. The scientific name of yeast is saccharomyces cerevisiac.
There are two types of yeast,
- Dry yeast
- Fresh or compressed yeast
Structure of yeast consists,
- Cell wall
Food: Food is a simple sugar like dextrose or fructose.
Suitable Climate: Need 80-85 degree F, and a minimum of 70% of humidity for the best result.
Fermentation Activity: The protoplasm of yeast contains following enzymes,
- Invertase converts sugar or sucrose into simpler forms of sugar which are inverted sugar. It is a combination of dextrose and fructose.
- Maltase helps convert maltose sugar into dextrose which will directly be fermented by yeast.
- Zymase is the most important fermenting agent which helps invert sugar and dextrose to break into carbon dioxide, a little amount of pure alcohol, and a small amount of glycerine, acetic acid, and little amount of lactic acid. It also produces flavourful aroma which gives fermentation flavor.
- Protease helps soften the flour protein which gets stretchability for the bread so it can get good volume and structure.
Storage of yeast: Yeast should be stored at 45 degrees F. The bacteria is killed if the temperature is between 127-140 degrees F.
Symptoms of Damaged or Rotten Yeast: The following are the symptoms of damaged or rotten yeast,
- Buttery consistency
- Brownish in color
- Crumbly in texture
- Very obnoxious smell
Chemical Leavening Agents
Chemical leavening agent is brought about by the production of carbon dioxide in a solution of acid and alkali, in the presence of heat.
Baking Powder: Baking powder is a leavening agent that is made of a mixture of an acid reacting salt with bicarbonate of soda. When the mixture is in dried condition starch is added to act as a separator between sodium bicarbonate and acid reacting salt till used.
In the heat and moisture, the salt reacts with sodium bicarbonate and releases carbon dioxide. When gas is entrapped into gluten structure or small air cell of the batter is developed because of the creaming action of fat. This structure expands with the production of gas and when baking the small parts of the gas gets absorbs by media itself. Cream of tarter is an actual form of refined tartar which is a by-product of precipitation from the grape wine manufacturing process.
Ammonium Carbonate: Ammonium Carbonate produces carbon dioxide in the presence of heat but because of the strong offensive flavor, it is always to be used with very strong flavoring agents.
Mechanical Leavening Agent
It is a mixture of air by beating, creaming, whisking, and sieving. Whisking of egg and sugar, creaming of fat and sugar, sieving of flour are the best examples of mechanical raising. All of the above actions involve physical movement hence it is known as mechanical raising or leavening.
Lamination or Water Vapour
The process lamination acts as raising procedure where the fat and dough is folded and rolled. When the moisture is incorporated in the fat and the dough also will vaporise during baking and give it the raising or lift.
This process is adapted by Indian cuisine like idles, dhoklas and utappam are steamed where heat helps to puff up the final product by vaporising the steam. Also in popcorn the corn is popped because of the moisture present in the corn and ultimately its volume is increased, and in choux pastry water vapour acts as raising agent which helps to cook in the oven.
Combination of All
Danish pastry is the best example of a combination raising where we use yeast in the dough and fat is used by the lamination process. Vanilla buns, fruit cake are some examples of the combination process where the use of whisking, creaming, and chemical raising agent are used to finish the product.