Hot food is important because it changes the food we eat. It has both historical and current significance.
The heat created during cooking is an agent of a chemical process called denaturation which changes the proteins in food, unravelling the molecules and altering their physical and chemical properties. Depending on the proteins cooked, this causes them to decrease solubility or to cause hydrophobic proteins to bond together to reduce the total area exposed to water. Denaturation affects what food feels like, tastes like, looks like and smells like. A fried egg quite clearly shows denaturation and is a good example – the runny, clear egg white (albumen) reaches a set consistency and turns opaque white when heated. As with many denatured proteins, the process cannot be reversed, i.e. you cannot go back to raw egg once it has cooled down.
The process of denaturation can be desirable because food can look, taste and smell better when cooked and the chemical changes can allow for the creation of new foods such as meringue. To create a meringue, the chemical bonds between the egg molecules need to be broken so that they can recombine with those of sugar.
Cooking has another function because it also kills bacteria, parasites and viruses, making the food we eat safer. Bacteria such as Salmonella and E. Coli can cause serious illness in humans and at the very least cause an unpleasant stomach upset. In the worst case scenario it can cause death. Children, the elderly, pregnant women and immuno-compromised people are at a greater health risk from serious illness from food-borne illness and thorough cooking helps make food safer for them.
The process of heating also softens food and makes it easier to digest. Cooked food contains the same amount of calories as uncooked food, but requires less energy to digest. Cooking makes starches more digestible. Starches aren’t soluble in water so they need to be heated to break them down (a process called gelatinisation). When they are broken down, they are easier for the digestive juices in the stomach to get to. Raw starch foods are also generally unappetising and hard (think raw potato) and cooking makes them palatable.
Hot food also helps warm us up and it is comforting. It’s much nicer coming home in the winter to a hot stew than coming home to a pile of raw vegetables.
We prefer to have hot food as part of our diet. That’s not to say that raw food doesn’t play an important part too – it’s just that humans like a mix of both and it benefits us to do this.
The ability to heat food was one of the things that helped mankind to evolve into the dominant species that it is today. Cooking allowed us to digest some food types more easily and we were able to kill off bacteria and parasites, giving us safer food. Without the discovery of fire and the ability to cook food, we would not be in the position we are now, and this means that the addition of hot food to the human diet was a very important step forward in our evolution.