Why does a boiled potato take longer to cook at high altitude?

Water boils at a lower temperature because air pressure is lower

The thin air is colder, so heat escapes faster

Water holds less oxygen at altitude

Starch absorbs less water in dry air

What makes a yeasted bread dough rise?

Carbon dioxide produced by the yeast

Oxygen folded in during kneading

Steam from the water in the dough

Why does long, slow cooking make a tough cut of meat tender?

Collagen in the connective tissue breaks down into gelatin

The muscle fibres soak up water and swell

Fat gradually converts into protein

Why does egg white turn from clear to opaque as it cooks?

Its proteins unfold and bond into a network that scatters light

The water in it evaporates and leaves salts behind

Why does chopping an onion make your eyes water?

Cut cells release enzymes that build a volatile sulphur compound

The juice is acidic enough to sting

Fine fragments of skin float up into the eye

Chilli heat is felt as burning because capsaicin binds to what?

A receptor that normally detects high temperature

The taste buds that detect bitterness

The nerve endings that sense pressure

The enamel surface of the teeth

Why does adding salt to a pan of water not make it boil noticeably faster?

It slightly raises the boiling point rather than lowering it

It lowers the boiling point but only above 2,000 metres

It has no effect on water at any concentration

It stops convection currents forming in the pan

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Food & Drink Hard ⚡ 10 Questions ⏱️ ~8 Mins +100 XP

The Science of Cooking

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Recipes tell you what to do. This quiz is about why it works, from the crust on a steak to the reason a stew needs hours rather than minutes.

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About this topic

Cooking is chemistry that happens to be edible. Heat unravels proteins so they tangle into new structures, sugars and amino acids react to build hundreds of aroma compounds that were not there before, and gas gets trapped in a stretchy protein net to make bread rise. None of it requires a laboratory, but all of it obeys the same rules one would. These ten questions cover the reactions a home cook runs into most often, and one or two that explain long-standing kitchen advice. The reason you rest a braise for hours, the reason milk beats water against a chilli, and the reason a boiled potato takes longer in the mountains all turn out to have short, precise answers.

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The Science of Cooking: all 10 questions and answers

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1The browning of a seared steak and of toast is chiefly which reaction?
- A Fermentation
- B The Maillard reaction Correct
- C Caramelisation
- D Oxidation
Answer: B. The Maillard reaction

Why: Amino acids and reducing sugars react under heat to create hundreds of new colour and aroma compounds. It is named after Louis-Camille Maillard, who described it in 1912 while investigating something else entirely.
2Why does a boiled potato take longer to cook at high altitude?
- A Water boils at a lower temperature because air pressure is lower Correct
- B The thin air is colder, so heat escapes faster
- C Water holds less oxygen at altitude
- D Starch absorbs less water in dry air
Answer: A. Water boils at a lower temperature because air pressure is lower

Why: At 2,000 metres water boils at roughly 93 degrees Celsius, so the food never gets as hot. A pressure cooker works the other way round, raising the pressure so water can pass 100 degrees without boiling off.
3What makes a yeasted bread dough rise?
- A Oxygen folded in during kneading
- B Steam from the water in the dough
- C Nitrogen released by the flour
- D Carbon dioxide produced by the yeast Correct
Answer: D. Carbon dioxide produced by the yeast

Why: Yeast feeds on sugars and gives off carbon dioxide and ethanol, and the dough traps the gas as bubbles. The alcohol boils away in the oven, which is part of what you smell while bread bakes.
4Which two wheat proteins combine with water to form gluten?
- A Collagen and elastin
- B Albumin and globulin
- C Glutenin and gliadin Correct
- D Casein and whey
Answer: C. Glutenin and gliadin

Why: They link into an elastic network once the flour is hydrated and worked. High-protein bread flour builds a stronger net and a chewier crumb, while low-protein cake flour deliberately builds a weak one.
5Why does long, slow cooking make a tough cut of meat tender?
- A Salt slowly dissolves the bone
- B Collagen in the connective tissue breaks down into gelatin Correct
- C The muscle fibres soak up water and swell
- D Fat gradually converts into protein
Answer: B. Collagen in the connective tissue breaks down into gelatin

Why: Collagen needs both heat and time, converting to gelatin over hours rather than minutes. That gelatin is also what gives a good braise its glossy, slightly sticky sauce.
6Why does egg white turn from clear to opaque as it cooks?
- A Its proteins unfold and bond into a network that scatters light Correct
- B The water in it evaporates and leaves salts behind
- C The fats in it crystallise
- D Air bubbles form throughout it
Answer: A. Its proteins unfold and bond into a network that scatters light

Why: Heat unravels the coiled proteins so they can tangle with each other, and the resulting mesh blocks light. Acid does the same job without heat, which is exactly how ceviche firms raw fish.
7Mayonnaise holds together as an emulsion mainly because of what in the egg yolk?
- A Gluten
- B Gelatin
- C Starch
- D Lecithin Correct
Answer: D. Lecithin

Why: Lecithin molecules have a water-loving end and an oil-loving end, so they sit on the surface of each oil droplet and stop the droplets merging. Add the oil too quickly and there is not enough lecithin spread around yet, which is when mayonnaise splits.
8Why does chopping an onion make your eyes water?
- A Fine fragments of skin float up into the eye
- B The onion contains capsaicin
- C Cut cells release enzymes that build a volatile sulphur compound Correct
- D The juice is acidic enough to sting
Answer: C. Cut cells release enzymes that build a volatile sulphur compound

Why: Damaged cells set off a reaction chain ending in a sulphur gas that irritates the eye, which then produces tears. A very sharp blade bursts fewer cells, and chilling the onion first slows the reaction down.
9Chilli heat is felt as burning because capsaicin binds to what?
- A The enamel surface of the teeth
- B A receptor that normally detects high temperature Correct
- C The taste buds that detect bitterness
- D The nerve endings that sense pressure
Answer: B. A receptor that normally detects high temperature

Why: Capsaicin activates TRPV1, a receptor that otherwise fires at temperatures above about 43 degrees Celsius, so the brain reads it as heat. It dissolves in fat rather than water, which is why milk clears it faster than a glass of water.
10Why does adding salt to a pan of water not make it boil noticeably faster?
- A It slightly raises the boiling point rather than lowering it Correct
- B It lowers the boiling point but only above 2,000 metres
- C It has no effect on water at any concentration
- D It stops convection currents forming in the pan
Answer: A. It slightly raises the boiling point rather than lowering it

Why: Dissolved salt actually raises the boiling point, by a fraction of a degree at kitchen quantities. Salt is added for seasoning, not speed.

Read alongside this quiz

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Browning, resting, salting, seasoning a pan. The handful of chemical processes behind nearly every rule in the kitchen.

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