Chemistry
The chemistry of cooking
Your kitchen is a chemistry lab: frying, baking and caramelising are reactions you can taste.
What you need first
Why does fresh bread smell so good? Why does a raw, wobbly egg turn firm and white in the pan? And why does cake batter rise in the oven? All of these are chemical reactions: cooking and baking transform substances into new substances, with new colours, new aromas and new textures. Your kitchen is the lab where you experiment every day, often without noticing.
Brown crust: the Maillard reaction
The brown, savoury crust on steak, bread and fried potatoes comes from the Maillard reaction: from about 140 °C, protein building blocks called amino acids react with sugars and form hundreds of new aroma compounds and brown pigments. That is why fried food tastes so much more intense than boiled food: in a pot of water at normal it never gets hotter than 100 °C, so the reaction never even starts. Its relative is caramelisation: heat pure sugar above 160 °C and it breaks down into brown, aromatic caramel, no protein needed.
The egg turns solid: denaturation
Protein are long chains folded into tiny tangles. The clear part of a raw egg is almost entirely water with about ten percent protein in it, and these tangles float around freely, which is why it is liquid and transparent. Heat makes the particles move ever more violently: the tangles unfold, the open chains catch onto each other and form a solid network. The egg turns firm and white. This process is called denaturation, and it cannot be undone: a fried egg never turns liquid again as it cools.
Water (liquid). Particles move faster.
Fluffy dough: raising agents
For cakes and bread to become light, they need gas bubbles in the dough. Raising agents such as baking soda or baking powder provide them: when baking soda meets an acid, such as lemon juice or yoghurt, the reaction produces the gas (CO₂). Baking powder is the convenient ready-made version: it already contains baking soda together with a dry acid, and the two only start reacting once liquid is added. The tiny bubbles inflate the dough, and during baking it sets around them. Yeast achieves the same by biological means: the fungi break down sugar and give off CO₂. That takes longer, which is why yeast dough has to rest before baking. Cut open a loaf of bread and you can see the bubbles as holes in the crumb.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
What is the name of the reaction that creates the brown, aromatic crust when frying?
Why does the white of an egg turn solid in the hot pan?
Why does a dough with baking soda and lemon juice rise?
Complete the sentence: heating pure sugar without any protein above 160 °C produces ….
The Maillard reaction starts at about 140 °C, but boiling water only reaches 100 °C. How many degrees Celsius short of the Maillard temperature is the water?
Match each kitchen process to its chemistry.