Leavening or raising means to increase the surface area of any dough or batter by creating gas bubbles inside the dough or batter. This also makes a product light in weight. The expansion of gas bubbles during baking increase the volume of the product and gives a desirable porous structure. Raising agents that are used in kitchen can classified into following categories:
- Biological (yeast)
- Chemical (baking powder, baking soda, baking ammonia)
- Mechanical (beating, whisking, creaming, sieving)
- Combination of all
Biological Raising Agent
Biological leavening agents are the ones that involve the use of some harmless micro-organisms in the process of leavening. Yeast or Saccharomyces Cerevisiae species is one such agent which produces carbon dioxide when added into food.
It refers to the various yeast strains used in baking bread and other bakery products. The primary function of yeast is to convert fermentable sugars present in the dough into carbon dioxide and ethanol. Baker’s Yeast is activated by adding it to a warm sugar water solution. The water must be warm & not too hot (which could kill the yeast) or too cold (which would not help in activating the deactivated yeast) Yeast growth can be slowed down or stopped using salt or some fats.
Yeast can of two types:
- Fresh or compressed yeast
- Dry yeast The scientific name of yeast is Saccharomyces Cerevisiae. Yeast is unicellular microscopic fungi.
The structure of yeast consist of:
- Cell wall
Food: Simple sugar like dextrose or fructose.
Suitable climate: 80 to 85 degrees F, at least 70% humidity can give the best result.
Fermentation activity: the protoplasm of yeast contains the following enzymes:
- Invertase: it converts cane sugar or sucrose into a simpler form of sugar which is known as invert sugar, which is a combination of dextrose and fructose.
- Maltase: it converts maltose sugar into dextrose which can be directly fermented by yeast.
- Zymase: this is the most important fermenting agent which breaks invert sugar and dextrose to carbon dioxide, some amount of pure alcohol, and a very small amount of glycerine, acetic acid, and some amount of lactic acid. It also produces a flavorful aroma which gives a pleasant fermentation flavor.
- Protease: it softens down the flour protein, thus giving a better stretchability for the bread (to be specific on gluten) to get a good volume and structure.
Storage of yeast: Stored at 45 degrees F. Yeast is killed by heat in a range of 127 degrees to 140 degrees F.
Symptom of damaged or rotten yeast:
- Buttery consistency
- Brownish in color
- Crumbly in texture,
- Very obnoxious smell.
The most popular drink in the world after water and tea is formed by the fermentation of starches mainly derived from cereal grains. Beer is also used as a leavening agent due to the presence of carbon dioxide in it.
It is a carbonated drink available as an alcoholic and non-alcoholic beverage. It is prepared by the natural fermentation of ginger, yeast, and sugar. It can be used in baking and other dishes involving leavening due to the presence of carbon dioxide in it.
Kefir, also called Milk Kefir or Bulgaros is a fermented milk drink made using kefir “grains”. Mildly intoxicating, this sour, carbonated drink is similar in taste to thin yogurt. Due to the presence of lactic acid bacteria and yeast, Kefir can be used as a good leavening agent in cooking and baking.
It is a form of bread made by the fermentation of dough using naturally occurring lactobacilli and yeast. It is mixed with flour to give the effect of leavening. The action of sourdough starters is slower than baker’s yeast and is generally not suitable for use in a bread machine.
Chemical Raising Agent
Chemical leaveners are made up with mixtures or compounds that release gases when they react with each other, with moisture or with heat. Most leavening agents are a combination of a salt of bicarbonate and an acid. The reaction of this acid and salt leaves behind a chemical salt. Chemical leaveners are used in cooking that requires a quick fermentation effect such as in breads and cakes. Most common chemical leavening agents are:
- Baking Powder:
It is a leavening agent made up of a mixture of an acid reacting salt with bicarbonate of soda. We also add some starch to the mixture to keep it in a dried condition and also to act as a separator between sodium bicarbonate and acid reacting salt, until used.
On the presence of both heat and moisture, the acid reacting salt reacts with sodium bicarbonate and releases carbon dioxide. A part of the gas is entrapped into the gluten structure or small air cells of a batter which already has developed because of creaming action of fat, these structures now expand with the production of the gas and during baking also and the small part of the gas is absorbed by the media itself.
Cream of tarter is actually a forum of refined tartar which is a by product or precipitation from grape wine manufacturing process
- Baking Soda
Also called as Bicarbonate of Soda or Sodium Bicarbonate, a fine white powder consisting of a mixture of alkaline salts. It is manufactured by adding carbon dioxide to huge vats of water containing sodium chloride and ammonia. When the resultant sodium bicarbonate settles at the bottom, it is filtered, washed in cold water, dried and ground to a fine powder. Baking Soda needs an acidic ingredient to activate it like molasses, honey, fruit/fruit juice, lemon juice, yoghurt etc.
Mechanical Raising Agent
It is incorporation of air by beating, creaming, whisking and sieving. Whisking of egg and sugar, creaming of fat and sugar, sieving of flour are the eg of mechanical raising. All these actions involve physical movement hence known as mechanical raising or leavening.
Creaming is also a leavening process where the sugar crystals are beaten together with solid fat. The sugar crystals cut through the structure of the fat integrating tiny air bubbles into the mixture. This process of leavening is mainly done in cookies.
- Whipping or Whisking
Whipping or Whisking is also a process of leavening where cream or egg whites are whisked vigorously to create a foaming action. This process is usually done in the making of sponge cakes.
Natural Leaving Agent:
Steam can be used as leavening agents for cooking that is done at very high temperatures. The batter must be capable of holding in the steam until it is set. Steam gives the effect of leavening as it expands upon heating. This way of cooking is generally applied in popovers and Yorkshire puddings.
Air is another leavening agent that can be incorporated by beating the batter thoroughly with Mechanical leavening agents. The trapped air expands upon heating.
Lamination acts as a raising procedure where the fat and dough is folded and rolled. The moisture incorporated in the fat and in the dough also will vaporise during baking and gives it the lift (or raising).
In indian cuisine , idlis and dhoklas are steamed where heat helps to puff up the final product by vapourising the steam. In popcorn, the corn pop because of the moisture present inside and ultimately its volume increase. In choux pastry water vapour acts as raising agent.
Combination Of All
Danish pastry is an example of combination raising where we use yeast in the dough and fat is used by lamination process. Some other eg are vanilla buns, fruit cake etc, where we use whisking, creaming and chemical raising agent.