Eduqas GCSE Food Preparation and Nutrition: Student Book

THE SCIENCE OF COOKING FOOD 79 SECTION 1 Sourdough Sourdough uses the natural yeasts in flour as a raising agent and is made using a ‘starter’ rather than commercially produced yeast. Sourdough bread tends to have a dense texture and a slightly tangy flavour. Gluten Gluten is a mixture of two proteins, gliadin and glutenin, found in wheat, rye, spelt and barley grains, and it is responsible for the elastic texture and structure of all doughs. When flour is mixed with water, the two proteins combine to create gluten particles, which come together to create stretchy gluten strands in the dough. The gluten strands in the flour need to be worked during kneading to become stronger and able to stretch. Gluten forms the structure of many different foods such as pasta, pastries, cakes and bread. Yeast-raised doughs and pasta use‘ strong ’ flour with gluten levels of about 12%+, so the dough can be stretched and expanded during kneading. Chemically risen baked goods such as cakes, biscuits, and scones use‘ soft ’ flour with 7-10% gluten levels because the mixtures do not need stretching and the mixtures should be handled gently to prevent gluten development . Over- worked gluten makes biscuits and pastry heavy and tough and batters rubbery. Emulsions We all know that oil and water do not mix. Some dishes we make need to have the oil and water permanently mixed together. To do this we create an emulsion . If you place olive oil and vinegar into a jar and shake it vigorously, a salad dressing is made. However, if the liquids are left in the jar to settle, the oil and vinegar will separate. This is called an unstable emulsion. By gradually beating egg yolk into the oil and vinegar solution mayonnaise is made which is classed as a stable emulsion. The egg yolk contains lecithin which is a good emulsifier. The oil and vinegar now cannot separate. Other emulsions are homogenised milk, butter and creamed cake mixtures. Foams A foam is a food that has been aerated , which means that a gas has been added to a liquid. Foaming denatures the proteins causing the food to become light and airy. Whisked egg white, whipped cream, marshmallow and soft scoop ice cream are very good examples of foams. Under-whisked egg white and cream become unstable and cannot hold the required shape. Over-whisked egg white protein denatures causing the food structure to lose volume and break down making the mixture very dry. Over-whisked cream ‘splits’ because the fat globules clump together forming butter. How to stop things going wrong At the start of this chapter we stated that having some food science knowledge can help us prevent errors from happening. It is best to understand what is happening when you are cooking rather than to rely on luck. There are a number of points that need to be learned to prevent your cooking from failing. Olive oil and vinegar in a jar – an unstable emulsion Make sure you understand the differences between soft and strong flour and their uses. Check it How well do you understand the terms ‘aerated’, ‘denatured’ and ‘globules’? Check it These egg whites have been aerated and the proteins denatured, making them stiff Gluten ball Cereals: Gluten formation  p184, What are sourdoughs and starters?  p191