Eduqas GCSE Food Preparation and Nutrition: Student Book

78 Chemical raising agents Most cakes and some biscuits need Carbon dioxide (CO 2 ) to create the baked light, airy texture. • Bicarbonate of soda + moisture + heat will create bubbles of CO 2 to raise the food. However, the food can have a slightly ‘soapy’ flavour so only use bicarbonate of soda in strong flavoured foods such as chocolate cake and ginger bread or biscuits. • Baking powder is a commercially made mixture of bicarbonate of soda + cream of tartar. Baking powder works the same as bicarbonate of soda, needing both moisture and heat to produce CO 2 . The inclusion of the cream of tartar stops the food having the ‘soapy’ flavour. The majority of the CO 2 gas is released once the mixture is heated. Baking powder is used in the ‘all-in-one’ cake method because it is quicker than using the traditional, lengthy creaming method. • Self-raising flour is plain flour with baking powder added in a correct quantity to suit most cake making recipes. Chemical raising agent experiment 1 Place 100ml cold water in a glass. 2 Stir in 1 tsp bicarbonate of soda. 3 State what happens. 4 Repeat steps 1, 2 and 3 using bicarbonate of soda and warm water. 5 Repeat steps 1, 2 and 3 using bicarbonate of soda and very hot water. Repeat the experiment using baking powder. Biological raising agent Yeast is a living organismgrown commercially for breadmaking and alcohol production. Yeast can bought either fresh or dried. Yeast +moisture + oxygen + food + time will produce masses of carbon dioxide gas bubbles. Bread needs lots of gas bubbles to raise the dough so yeast is the perfect raising agent when breadmaking. To make bread the yeast is added to strong flour and water to form a dough. After kneading the dough must be left to rise or‘ prove ’in a warm environment allowing the yeast to do its work. The yeast is activated by the warmth, oxygen andmoisture found in the dough and it feeds on the natural sugars in the flour creating the carbon dioxide gas bubbles. This process is called fermentation . As the dough rises the gluten strands in the flour form a complex mesh trapping the gas bubbles which creates a soft, spongy doubled in size dough. Traditional bakers knock back the risen dough and give it a second proving. This helps give a better flavour and creates a uniform, finer texture to the finished bread. Yeast experiments You will need: 6 test tubes labelled A-F 6 balloons – to seal each test tube 1 test tube rack 6 x ½ tsp dried yeast 2 x ½ tsp sugar 1 x ½ tsp salt ½ tsp yeast in each test tube Observations after 10 mins / 20 mins A Add 4cm cold water B Add 4cm warm water C Add 4 cm very hot water D Add 4 cm cold water + ½ tsp sugar E Add 4 cm warm water + ½ tsp sugar F Add 4 cm warm water + ½ tsp salt Fresh and dried yeast Fermenting yeast Cereals: The importance of yeast  p190 Make sure you understand how yeast raises a baked product. Check it Make sure you understand how baking powder raises a baked product. Check it Yeast experiment: Look at the liquid in the test tubes after 10 minutes – make notes on what you see. Look at the liquid in the test tubes after 20 minutes – make notes on what you see. After 20 minutes look at the balloons: Which balloon/s has inflated the most? Why do you think this is? Which balloon/s has not inflated? Can you explain why? Activity CORE KNOWLEDGE