Is baking a cake an art or science, or both? The beautiful icing, sugar glaze, towering layers, fruit arrangements on the top and the fondant are all real work of art. However, the cake itself is a work of chemistry without which there will be no aroma, flavour, colour, porous texture, and the fluffiness.
The diverse ingredients used to bake a cake react with each other through a series of chemical reactions. Flour, sugar, egg, milk, baking powder and butter – each has a role in these reactions.
Wheat flour is used in most cakes, and it contains both starch and a type of protein called gluten. Gluten holds all the ingredients together. It also stretches as gas is produced by baking powder and baking soda. Baking soft cakes requires the right amount of protein in the flour because softness reduces as the amount of protein is increased. Cake flour is 7.5% protein, while all-purpose flour and bread flour is 10.5% and 12% protein respectively. Now you know why breads are slightly harder than cakes. Let us see how all other ingredients react with this flour to form a tasty, fluffy, and aromatic cake.
Baking soda and baking powder are the leavening agent that makes a cake rise. Baking soda or sodium hydrogen carbonate is an alkali. It reacts with the acid in the batter and produces carbon dioxide. The release of this gas makes the cake rise. Next time watch a cake rise through the oven glass while the cake is baking. Baking powder which is sodium bicarbonate has additional acidic salt and releases twice the amount of carbon dioxide. This happens when baking powder comes into contact with water and then again when temperature rises. The high temperature helps baking powder to produce tiny bubbles of carbon dioxide that creates the porous texture.
Sugar gives the sweetness to cakes. This is common knowledge. Here is the science. At temperature of 160°C, sugar undergoes Maillard reaction involving proteins in eggs and flour. Maillard reaction results in browning of the batter and forms the beautiful crust in baked foods. The flavour and aroma from baked goods are also from this reaction. The next time you see the brown crust on a bread loaf, think of Maillard reaction, the sugar and protein.
Let us see what butter or margarine do in a cake. If you watched anyone baking, butter is creamed with sugar during which it traps the air. This makes cakes light. Fat helps in browning and in heat transfer throughout the cake.
Eggs are the source of protein for Maillard reaction. Eggs are also the emulsifiers that play the role in combining ingredients that do not mix well like oil and water. Creamed cake batter has a smooth consistency that combines well because of eggs. The protein in eggs too gives the beautiful golden colour when baked.
Liquid like milk plays a role too. They help in the chemical processes to take place by hydrating the protein, starch and baking soda and baking powder. Vaporisation of liquid during the baking process releases steam that further increases the volume of the cake, making it fluffy and gives the right amount of moisture.
Another chemical process that takes place at high temperature is caramelisation that happens at 180°C. This is the final stage of the baking process. Caramelisation causes sugar molecules to breakdown, releasing water and steam is produced. The compound that is produced is called diacetyl, which gives the butterscotch flavour and aroma. Further caramelisation produces ester and lactones, and finally furan is produced that gives the nutty flavour, and maltol that gives the toasty flavour.
Since there is a lot of chemistry involved, baking a perfect cake requires the right amount of ingredients and the steps must be followed precisely. Too much of any ingredient will affect the reactions and this is the reason for cakes that sink, not soft or flavourful enough.
The next time when you indulge in a cake, have a closer look at the caramelised crust, fluffy texture, the aroma, and the nutty and toasty flavour, then think about all the ingredients and their chemical reactions.