Why Do We Cook Food?

The most immediate reason is safety. Heat kills most bacteria, parasites and viruses that cause food borne illness, which is why cooking temperatures for meat and eggs are specified so precisely in food safety guidance.

The second is digestion. Heat breaks down tough plant cell walls and denatures proteins, unfolding them so digestive enzymes can reach them more easily. Cooked food yields more usable energy for less digestive effort, which has been measured directly in feeding studies.

Cooking triggers a set of physical and chemical changes:

• •Proteins denature and coagulate, firming meat and setting eggs
• •Starches gelatinise, absorbing water and becoming digestible
• •Collagen in tough cuts converts to gelatin during long slow cooking
• •The Maillard reaction and caramelisation create hundreds of flavour compounds
• •Cell walls in vegetables soften, releasing nutrients

The primatologist Richard Wrangham argued that cooking was central to human evolution. Compared with other primates our teeth and jaws are small, our guts are short, and our brains are enormously expensive to run.

His argument is that cooked food, being softer and more energy dense, allowed the digestive system to shrink while freeing energy for a larger brain. Chewing time supports the point: chimpanzees spend around half their waking hours chewing, while humans spend a small fraction of that. The dating of controlled fire use is debated, which is the main open question in the theory.

Cooking is not purely beneficial. Vitamin C and several B vitamins are heat sensitive and degrade, and water soluble nutrients leach into cooking water if it is discarded.

Very high temperature cooking also creates some undesirable compounds, including acrylamide in browned starchy foods and certain compounds in heavily charred meat. Food safety agencies suggest cooking to golden rather than dark brown and avoiding burnt portions, which is a modest adjustment rather than a reason to change how you eat.

The assumption that raw is always healthier does not hold up. Cooking tomatoes increases the availability of lycopene substantially. Cooking carrots improves access to beta carotene. Cooking spinach reduces oxalates that block calcium and iron absorption.

Some foods are effectively inedible raw. Kidney beans contain a toxin that requires proper boiling, and many staple root vegetables need cooking to be safe or digestible. The sensible position is that some foods are better raw, some better cooked, and variety handles it.

Beyond biology, cooking has social consequences that anthropologists have written about extensively. Cooking requires a fire, and a fire is a fixed location that people gather around and return to.

It also introduces delay between acquiring food and eating it, which creates opportunities for sharing, division of labour and food being kept for others. Most primates eat as they forage, individually and immediately. The hearth turns eating into a scheduled communal event, and a large amount of human social structure has been built around that pattern ever since.

The cooking hypothesis depends on when people began controlling fire, and that is hard to establish. A campfire leaves little behind: ash, charcoal, burned bone, reddened soil and stone tools cracked by heat. The main difficulty is telling a hearth apart from the traces of a natural wildfire or from burned material washed in by water. Researchers therefore look for burning concentrated in one spot, repeated over time, and closely associated with human tools and food remains.

Modern methods help. Microscopic study of sediment can reveal plant ash and tiny fragments of burned bone, while heated flint can be dated and its heating temperature estimated. Some of the oldest widely discussed evidence comes from Wonderwerk Cave in South Africa, where ash and burned bone deep inside the cave have been dated to around a million years ago. Other sites are younger, and researchers still debate when fire use became regular rather than occasional.

Not every method that looks like cooking works like heat. In ceviche, raw fish is soaked in lime or lemon juice. The acid denatures the proteins, so the flesh turns opaque and firm as though cooked, but acid is far less reliable than heat at killing bacteria and parasites. This is why fish served raw or in ceviche is often frozen first in commercial kitchens, since deep freezing kills many parasites. Curing with salt, smoking and fermentation also change food and help preserve it, but each works by its own mechanism.

Boiling seems simple today, but it needs a container that can survive heat, and heatproof pottery is much younger than the human use of fire. Before pots were common, people could still boil food by stone boiling: heating stones in a fire and dropping them into water held in a pit lined with hide or in a tightly woven basket or wooden vessel, adding fresh hot stones to keep it bubbling. Earth ovens, pits in which food is buried with hot stones and covered, were another widespread method and are still used for feasts in parts of the Pacific.

Making food safe depends on time as well as temperature. Killing bacteria is not like flipping a switch at one temperature; the hotter the food, the faster they die. UK food safety guidance treats 70 degrees Celsius held for two minutes in the centre of the food as a safe standard, but it also accepts equivalents such as 65 degrees for ten minutes or 60 degrees for about 45 minutes. This is how sous vide cooking works. Meat is sealed in a bag and held in a water bath at a moderate temperature for long enough to make it safe, while staying juicier than meat cooked at higher heat.

Where the bacteria sit also matters, which explains a common puzzle. In a whole steak, harmful bacteria are found mainly on the outside surface, because the inside of intact muscle is normally close to sterile. Searing the outside kills them, so a steak can be served rare in the middle. Mincing changes that. When meat is ground, surface bacteria are mixed all the way through, so a burger needs to be cooked thoroughly in the centre, with no pink meat and juices running clear. The same reasoning applies to rolled joints and to any meat that has been pierced or mechanically tenderised.

Boiling water seems like a fixed point at 100 degrees Celsius, but that is only true near sea level. The temperature at which water boils depends on the air pressure pressing on its surface, and pressure falls as you climb. At around 3,000 metres water boils at roughly 90 degrees, and on the summit of Everest at only about 70. Since cooking depends on the temperature the food reaches rather than on the bubbles, pasta, rice and dried beans take noticeably longer in high mountain towns, and some foods struggle to soften at all at very high altitude.

A pressure cooker uses the same physics in reverse. Its sealed lid traps steam, raising the pressure inside to roughly twice normal air pressure, and water then boils at about 120 degrees. Those extra 20 degrees greatly speed up the softening of tough cell walls and the breakdown of collagen, so dried beans or a beef stew can be ready in a fraction of the usual time, which is why cooks at altitude rely on them. Baking needs adjusting at height too, because lower air pressure lets the gas bubbles in dough and batter expand more, so recipes often reduce the raising agents.

We cook food to make it safer, more digestible and better tasting, the extra available energy may have supported the evolution of our large brains and small guts, and cooking increases the nutritional value of some foods while reducing it in others.