Eduqas GCSE Food Preparation and Nutrition: Student Book

THE SCIENCE OF COOKING FOOD 77 SECTION 1 RAISING AGENTS What will I learn? • Why raising agents are used in baking and how they work • The different types of raising agents • What happens if too much raising agent is used Why raising agents are used in baking Raising agents are added to most baked products during the making process using gas, air or steam which, when heated, expands causing the food to swell and rise up. Raising agents produce a risen, light and airy texture in the food. Unleavened products don’t use a raising agent. Types of raising agent Mechanical raising agents Air will expand when heated is incorporated into the recipe through: • Sieving flour will trap air. Used in pastry, cakes or batters. • Whisking eggs. Whole egg plus caster sugar or egg whites, when whisked, will trap a large volume of air creating a foam. The mixture must be cooked immediately to set and stabilise the foam. Egg whites create a stiff foam and will be stabilised by the addition of a drop of lemon juice (acid) or some sugar. The foam is formed due to the unravelling and stretching of the protein, ovalbumin, creating the increased volume. Unstable foams lose the air particles very easily and become liquid again. Whisked eggs are used in meringue, mousse, sponge cake to give a very light texture. • Rubbing fat into flour will incorporate a little air. • Creaming fat and sugar together traps minute air bubbles. The fat becomes pale in colour and the mixture looks creamy. • Lamination – air is trapped each time flaky and rough puff dough is rolled and folded to create the layers. Experiment to trap air 1 Place 200g flour in a measuring jug. 2 Mark the level of flour on the jug. 3 Sieve the flour onto a piece of greaseproof paper. 4 Carefully pour the flour back into the jug. 5 Mark the level of flour on the jug. 6 Repeat steps 3, 4 and 5. Has the volume of flour appeared to increase? Explain your findings. Physical raising agent Steam is created in products such as Yorkshire pudding and choux pastry which contain large quantities of water. The high temperature of the oven turns the water to steam forcing it through the mixture, pushing or raising it upwards. The heat of the oven then sets the egg and flour creating a hollow, risen food. The oven must be hot for the steam to be created quickly before the egg and flour ‘set’. Opening the oven repeatedly during cooking or removing the food too early will cause the food to collapse. Whisked egg white foam Yorkshire puddings Choux pastry Make sure you understand how air, steam and baking powder raise a baked product. Check it Make sure you understand how steam raises a baked product. Check it