Raising agents

 Raising agents

                     The function of a raising agent is to puff up the food so that it spreads and rises, thus making it light instead of close and heavy. The tiny air spaces caused by the raising agents are retained during the process of cooking. The leavening of the flour mixture is accomplished by the expansion of incorporated air and by the internal production and 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 micro-organisms or chemical agents. During the first part of heating, gas production is accelerated and the gas formed expands as the temperature rises. Gluten, a substance found in flour, develops when moisture is added, and helps to keep the raising agent within until the food sets, thus helping to make the food light. 

                           Gluten is a sticky, elastic substance which stretches as the air or gas expands and prevents these from escaping. The air or gas trapped in the mixture expands further when heated and makes the cooked food light. Too much raising agent raises the food too rapidly, breaks the surface and allows the gas produced to escape, and as a result the product sinks and becomes heavy.

Air as a raising agent - Air is incorporated by sifting flour, by creating shortening, by benting 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.

Chemicals as raising agents - Chemicals such as sodium bicarbonate, cream of tartar, baking powder, ammonium enrbonate, etc., are added to mixtures to make food light. In each case the result in the production of carbon dioxide.

                Baking powders are mixtures of sodium bicarbonate with some suitable acid anche creom of tartar, diluted with cornflour to give a product the desired strength. The cornflour also serves to separate the acid and the base, thereby increasing the stability of the mixture during ahelf life. General proportions used are 1-2 tsp baking powder per 450 gin of foundation.

        

                    The richer the mixture, the less the haking powder required. When the mixture is of an acidic nature, Cas when sour milk, Buttermilk, treacle, vinegar or jams made from acid fruits are used) the addition of cream of tartar or tartaric acid in not necessary, since the soda will act upon these other foods and cause the required gas to be given off. Four tsp baking powder is equal to approximately one tap of soda in a carbon dioxide yield. In certain flotu mixtures variations from neutrality are deliberately sought by including a reaction with either soda or cretim of tartar, eg, to get the dark, rich colour in chocolate cakes which mony people prefer, sodium bicarbonate is used.

By the addition of yeast -  Carbon dioxide is produced either from sugar by yeast, or from a carbonate, usually sodium bicarbonate, by action of an acid.

               Yeast consists of microscopic, unicellular plants which are capable of rapid multiplication when conditions are favourable and which obtain energy by breaking down stugars to carbon dioxide and alcohol. This process is known as fermentation, and is brought about by the enzyme zymase found in yeast. Yeast also produces engymes which are able to split disaccharide sugars.

Dried yeast - This in a mixture of yeast and cornflour or cornmeal pressed into cakes and dried. The yeast continues to live but in an inactive state. When furnished with warmth and moisture, it begins to develop and multiply, but this process is slow. Dried yeast has to be soaked in lukewarm water and mixed with very soft dough (sponge) for a preliminary period of development before all the other ingredients are added.

Activated dry yeast - This develops more rapidly than dried yenst and is the type now available It can be used in straight dough mixing. It is legs perishable than compressed yuust. The whole life of both dried yeast and activated dried yeast is longer at refrigerated temperatures than at room temperature.

Compressed yeast -  This in a moist mixture of yoast plants and starch The yonst remains active and will grow and multiply rapidly when added to dough. It has to be kept at refrigerated temperatures and keeps well for only a few days. If held in the freezing compartment, it retains its activity for a longer period.