LeaveningLeavening is a chemical reaction that can be defined as: the process of incorporating one or more gases into a product, causing it to rise. Leavening can be done through various methods, including physical/mechanical (whisking, beating), chemical (leavening agents - baking powder, sodium bicarbonate) and biological (yeast).
The pictures to the right are examples of foods that require leavening to be made. |
In this recipe... |
Butter and self-raising flour are the two ingredients in this recipe involved in leavening. The gases incorporated into butter are put there by physical/mechanical means. Self-raising flour incorporates gases through chemical means. Self-raising flour contains baking powder. Baking powder is made up of sodium bicarbonate and tartaric acid. Leavening through self-raising flour relies on the fact that when an alkali (bicarb soda) and an acid (tartaric acid) come into contact with water, they produce CO2.
Analysis of chemical reaction in method: In step 3, when the butter and caster sugar is being creamed, air is beaten into the butter by the electric beaters. This is the first stage of leavening and creates a colloidal dispersion of air in fat. The self-raising flour that incorporates chemical leavening is added in step 5, along with milk, the liquid that is involved in the chemical reaction creating CO2 when it is mixed with the flour. In step 6, the batter is placed into the cake tin, so that it can rise in the oven. When a cake rises, it relies on the principle that gases expand when they are heated, so the gases inside the cake batter will make it rise. This is why it is important not to let all the gases escape by banging the batter on the counter too long, and scraping batter along the sides of the tin will make the cake expand from the side, which interrupts the rising of the cake batter on the bottom of the tin. In step 7, the cake is baked. The gases in the batter will expand, making the cake rise as well. During this step, another chemical reaction coagulation occurs. The coagulation in this recipe is due to the egg because it is a source of protein. When the egg in the batter coagulates, the shape of the cake sets as well, and helps with the cake's structure after the gases trapped in the batter have expanded and escaped. |
Physical changes |
There is a colour change in the butter due to leavening when it is being creamed by the beaters. The butter turns a pale colour when air is added into it. There is also a colour change in the cake batter after it has been through the oven (turns from pale to brown), but this is not a change resulting from leavening.
Any changes in aroma in this recipe would not be caused by leavening, but adding passionfruit and lemon zest give the final product a nice aroma. There would not be taste changes in this recipe due to leavening but the cake batter would taste different before and after it has been through the oven. The cake's appearance would change due to leavening, The cake batter would rise while it is in the oven, as shown in the diagram in the section above. This causes the baked cake to appear larger in volume than the batter. The texture of the cake would have changed due to leavening. The final product would be light and airy because of the air pockets in the cake, instead of dense in texture. |
Evaluation of recipe
The chemical reaction leavening is important in ensuring the success of the creation of lemon and passionfruit cake. It creates the light texture of the cake and makes it larger in volume and without it, the cake would be very flat and compact.
Physical properties of the cake are altered by leavening and help to improve the eating quality of the cake. The most significant change is the change in texture and volume. Even though the cake could still be made without leavening, the chemical reaction makes the cake better to consume.
Two factors that can determine the success or failure of the chemical reaction are the ratio of self-raising flour to the other ingredients and the amount of time it spends in the oven. If there isn't enough flour, the cake will not rise enough. To properly measure flour, make sure that there are no air pockets when using a measuring cup and smooth the top off with a butter knife. The amount of time the cake spends in the oven is vital. While it looks like leavening has finished occurring at a bit over half the time it takes to bake, the chemical reaction coagulation will need to occur to make sure the structure of the cake stays in place, or the physical changes of leavening would have been unsuccessful. A timer or clock is highly recommended to make sure the cake spends enough time in the oven.
Physical properties of the cake are altered by leavening and help to improve the eating quality of the cake. The most significant change is the change in texture and volume. Even though the cake could still be made without leavening, the chemical reaction makes the cake better to consume.
Two factors that can determine the success or failure of the chemical reaction are the ratio of self-raising flour to the other ingredients and the amount of time it spends in the oven. If there isn't enough flour, the cake will not rise enough. To properly measure flour, make sure that there are no air pockets when using a measuring cup and smooth the top off with a butter knife. The amount of time the cake spends in the oven is vital. While it looks like leavening has finished occurring at a bit over half the time it takes to bake, the chemical reaction coagulation will need to occur to make sure the structure of the cake stays in place, or the physical changes of leavening would have been unsuccessful. A timer or clock is highly recommended to make sure the cake spends enough time in the oven.