Chemistry cake picture

Published on November 5th, 2016 | by Alice Rossi

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The Wee Scottish Science Off: Cake Week — A Tutorial

We are going to make a cake in the most informative way possible. Be warned, much of what happens cannot be credited to you (shame, I know). Baking is an incredible balancing act. You need all the ingredients but, more than anything, you need them to be present in the right proportions.

Baking is an incredible balancing act. You need all the ingredients but, more than anything, you need them to be present in the right proportions.

For a plain cake, a delicious conglomerate of sweet buttery crumbs, you will need: butter, sugar, self-raising flour and eggs in a 1:1:1:1 ratio (assume each egg weighs about 50g) and a pinch of salt.

Fats first!

Start by creaming together the butter (at room temperature) and sugar. This step is crucial to the formation of air bubbles, which will make the cake fluffy and light. The final result should be rather foamy, as the fats in the butter coat the newly formed bubbles and preserve them. The smaller the sugar granules, the more bubbles can form, which is why caster sugar is preferred to its cheaper granulated brother. Now add a pinch of salt; this will help strengthen the gluten network between your precious bubbles and enhance the overall sweetness.

It’s egg o’clock!

Whisk your eggs together until the fatty nucleus (yolk) looks evenly incorporated into the protein-rich cytoplasm (egg white). The eggs’ main mission will be to provide an additional coat to the air bubbles. This will harden when heated, preventing the air from escaping and becoming lost forever.

British vs. Continental Baking

Now, if you’ll allow me, I’d like to open a little bracket. According to my non-British baking background, eggs should be added first. I was taught first to whisk sugar and egg yolks until white and fluffy while the egg whites, whipped until firm, are supposed to be added only at the end.

According to my non-British baking background, eggs should be added first. Based on my experience, neither of these techniques is incorrect, but they yield different results. Following the second method, you often won’t need a chemical rising agent to achieve cloud-like fluffiness.

Based on my experience, neither of these techniques is incorrect, but they yield different results. The cake resulting from the first one is a trustworthy sponge cake which can be filled with cream, jams and coated with icing. The second one instead is much lighter, “genoise”-like, and tends to require less butter as not to squish the delicate bubbles from the egg whites.

Following the second method, you often won’t need a chemical rising agent to achieve cloud-like fluffiness.

Back to our original recipe.

It’s now time to add in flour. This has to be done in the most delicate way possible so as not to disrupt the bubbles. Some like to sift it first, to break off lumps and facilitate the incorporation of the individual particles. The starch in the flour will stabilise the egg foam, while flour proteins will create a gluten network, responsible for the elastic and firm structure of the baked product. Gluten requirements for cakes are not as extensive as those for bread, which is why cake flour usually uses low-protein wheat. As soon as the flour looks evenly incorporated, stop mixing! If the batter is over-mixed, the end result will be a cake tougher than a convicted rhinoceros, due to the excessive gluten formation.

As soon as the flour looks evenly incorporated, stop mixing! If the batter is over-mixed, the end result will be a cake tougher than a convicted rhinoceros due to the excessive gluten formation.

Once you are done, delicately pour the batter into a greased tin and place it in a preheated oven at 180°C. The baking time depends on the size and depth of the tin, but it should be around 30 minutes. While trying to resist the impulse of opening the oven before the cake is done, sit back and relax with the latest copy of AU Science.

While you relax the real sorcery is happening inside your oven.

The air bubbles you trapped into the batter begin to expand, stretching the gluten around them. The rising agents in the self-raising flour react and release CO2, making the bubbles even larger. As the heat increases water turns into vapour, further boosting the size of those bubbles into a plethora of rotund madness.

The rising agents in the self-raising flour react and release CO2, making the bubbles even larger. As the heat increases water turns into vapour, further boosting the size of those bubbles into a plethora of rotund madness.

When the batter reaches 80°C the egg proteins coagulate, starch absorbs moisture and the gluten becomes more rigid, giving the cake its final structure. It is on the now dry surface that the sugar caramelises, giving the cake its golden colour and delicious smell.

We now approach the end of our journey. You can now take a peak and open the oven door. Poke your beloved creation—or stab it if you like (responsibly)—it should feel quite sturdy. The knife should come out clean. Take the cake out of the oven and let it cool slightly before digging in; this lets the fats in it cool down and turn back to their solid form.

You produced a cake. A glorious, wonderful cake.

Featured image by fenwench (CC BY 2.0) at Flickr.

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