Presentation on theme: "Raising Agents Raising Agents are gases which are introduced into a food mixture : During the mixing process In a substance which is added to the mixture."— Presentation transcript:
1 Raising Agents Raising Agents are gases which are introduced into a food mixture :During the mixing processIn a substance which is added to the mixtureThe gas is incorporated or released when ingredients are combined.On heating (baking), the minute bubbles of gas enclosed in the mixture expand, causing the mixture to rise.
2 The three most common raising agents are steam, air and carbon dioxide. They are frequently used in combination with each othere.g. in a creamed cake mixture :-Steam from liquid (egg/milk/water)Air beaten in (creaming butter & sugar)Carbon dioxide from chemical raising agents in baking powder or self raising flour.
3 SteamSome food products have steam as the main raising agent. These products must contain a high proportion of liquid, e.g. Choux pastry, batter used for Yorkshire puddings.For steam to make the mixture rise, two conditions are needed;A large proportion of liquid (Milk/Water)A high baking temperature of 200oC or aboveDuring baking;Liquid reaches boiling pointSteam forces its way up through the mixture, stretching the mixture and making it rise.The steam escapes and is replaced by air, the mixture bakes and sets into the risen shape.Sometimes steam is trapped inside. It condenses on cooling and then the product collapses. This often happens in Yorkshire puddings.
4 AirMechanical action incorporates air into mixtures, it is the main raising agent in some food products, e.g. whisked sponge cakes and souffléAir can be mechanically introduced into mixtures by;Sieving flour – air is trapped between fine particlesRubbing fat into flour – air is trapped between breadcrumbsCreaming fat and sugar – air is beaten in, to form an air and fat foam.Whisking eggs/sugar or egg whites – air is whisked ino the egg to form a high volume foamBeating batter – air is beaten in, but steam is the main raising agent.Rolling and folding pastry – air is trapped between the layers
5 Carbon Dioxide This is produced in two ways; Biologically – from yeast cells during the fermentation processChemically from the action of bicarbonate of soda with an acid
6 Biological Raising Agents Yeasts are micro organisms, during the fermentation process, the yeast cells feed on sugar and reproduce to produce carbon dioxide.Certain factors affect the action of yeast :-Temperature – optimum temperature range is 25oC – 35oCAbove 60oC the fermentation process is destroyedBelow 25oC the reaction is slowed downFresh yeast can be frozen without killing it and it becomes active again once defrosted.Moisture – This is provided from milk/water/eggFood – During fermentation of yeast, the cells need to be fed on sugar to produce carbon dioxide. There is also a small amount of sugar in the flour
7 Chemical Raising Agents Carbon dioxide is produced from chemical reactions. This can be made to happen in many recipes by the addition of a chemical raising agent.Chemical raising agents must be measured accurately, they ;Are used in small quantitiesAre easy to use and often already combined – e.g. self raising flourWill produce controlled amounts of carbon dioxideto aerate mixtures evenly.Three types of chemical raising agent are :-Bicarbonate of Soda – known as sodium bicarbonateBicarbonate of Soda & Acid (alkali & acid)Baking Power or baking powder in self raising flour
8 Bicarbonate of Soda :-Simplest type of chemical raising agent. When heated in a mixture, it produces sodium carbonate (soda) steam and carbon dioxide.The carbon dioxide and steam aerate the mixture. The soda leaves a dark yellow colour and gives a sharp alkaline taste to the mixture.Used in recipes which have other strong flavoured ingredients e.g. chocolate cake & gingerbreadBicarbonate of Soda plus AcidThe bicarbonate of soda reacts with the acid to produce carbon dioxide. The acid helps to neutralise and prevent the taste and colour residue left when bicarbonate of soda is used on its own.A traditional source of acid is sour milk. This is still used in some mixtures, an other sources of acid is Cream of Tartar (Tartaric Acid), when combined with bicarbonate of soda this releases the carbon dioxide slowly, leaving a tasteless salt behind. The ratio used is 2 parts Tartar to 1 part bicarbonate of soda.Baking PowderCommercial mixture of bicarbonate and acid substances ready mixed in the correct proportions. A buffer is added in the form of cornflower or rice flour to absorb any moisture and prevent the reaction taking place in the storage container.Baking powder is added to plain flour to produce self raising flour.