Why Does Roast Chicken Taste So Good? Inside the Science Behind the Flavors We Love

When we cook our favorite meals, what happens to the carbo-hydrates, proteins and fats? I confess I am a less-than-average cook, but God loves a trier. I remember being about 23 years old and trying to cook a chicken from scratch, and I mean really from scratch, in that the chicken was alive at the start of the process. Most people in London are unlikely to have killed a chicken and so it is not a skill I came equipped with.

I was in our bright windowed kitchen in Owerri, south-east Nigeria. It had just stopped raining and the air was still humming with moisture, the mud outside our single-story house was thick with the watering. I had just started work as a research fellow in pharmacy in Lagos and I was enjoying the shiny laboratories of the university, full of coveted equipment. As well as teaching students how to measure and measure again the components of medicines, I was also working as a research assistant on a project that was looking at what happens to a painkiller called naproxen when it was taken and documenting how it was broken down by the body’s enzymes.

However, on this day, I was home for the holidays, visiting the family, and had offered to make dinner.

After taking a sharp blade to the chicken’s neck, I’d then poured hot water on the chicken in an effort to uncurl the skin proteins and loosen the feathers ready for plucking. As soon as the hot water made contact with the chicken, the bird realized it wasn’t dead after all and, on the contrary, very much alive. It immediately made a bold leap for freedom through the tiny window opening in our family kitchen. It all happened in a flash. One minute, there was calm, with me humming a tune, and the next minute, the atmosphere was rudely punctured by a flurry of feathers, loud smashing noises against the partially open window and manic clucking. The fowl’s head was still stubbornly attached. The chicken had only feigned death to put me off my game.

We need fats in our diet as, remember, the fats we eat end up being used by our cellular enzymes to make all the specialized fats that the cells need.

My father was furious when he got home. He lamented the loss of the star of our dinner, decried the chicken’s painful suffering and chastised me for my obvious incompetence. He continued his sweaty complaints as we settled into a meal of chicken soup without the chicken. As we chewed wordlessly and sulkily on our vegetables, I decided not to regale my dad with the joys of the naproxen waste products that I had found in human urine.

When I had attempted to put that chicken in a pot of steaming hot water, I was trying to use heat to break the weaker bonds that make the proteins in the chicken keep the chicken’s shape. Breaking down these bonds would have made the proteins easier to digest. Heat just makes every molecule that little bit easier to handle for our digestive enzymes, so that our stomachs and intestines can turn the long polymers of carbo-hydrates and proteins into smaller molecules that can cross our gut membranes and go on to build new cells, nourish old cells and provide energy for a whole host of biological processes that are going on each and every second of our day. The application of heat really changes the carbohydrates, proteins and fats in our food for the better.

Starch is present in raw food as starch granules. If you look down a microscope at a slice of uncooked potato, you will see that starch is arranged in visible tiny granules, sitting in highly ordered crystals. Solid starch granules consist of starch polymer chains linked to each other by weaker physical bonds. Once starch is heated, this organization starts to fall apart as the starch molecules are hopelessly separated from each other, free to roam; the weaker bonds holding the molecules in a strict ordered state are now broken.

While the starch molecules maintain their length initially, they lose the three-dimensional granule arrangement and disperse in the water in a process known as gelatinization, bursting forth from the starch granules in joyful exuberance. We can see starch molecules making sweet connection with the cooking water when we cook potatoes or rice, the cloudy nature of the water is all down to the freeing of starch molecules from their holding cells. At this point, the starch chains become shorter. Shorter starch polymers mean that there is less work for the enzyme amylase to do when it attacks the starch molecules as we chew our potatoes, boiled, roasted or fried. This enzyme sits around in our saliva, waiting expectantly for starch molecules, eagerly breaking them down once they make an appearance. Amylase starts work right away, as soon as we crunch into our starchy lunch, reducing these starches into glucose molecules while they are still in in our mouth. These glucose molecules are easier to absorb into our blood, as they are now nice and small compared to the starch polymer.

Once we’ve chewed our food, it makes its way down to our stomachs. The amylase stops work once it enters the acid environment of our stomach with our food. At this point, a new form of amylase is secreted by our pancreas and continues to break down the starches when they enter our small intestines. The acidity in our intestines is much lower than that in our stomachs, the most acidic region of our bodies. On a pH scale, where a pH of 1 is very acidic and a pH of 14 is very alkaline, the pH of our stomachs is about 1 and the pH of our intestines is about 7. Our guts become less acidic as we head from our stomachs to our colon.

This acidity in our stomach is protective. As our stomach is the first stop for our food on the gut express after consuming our meal, this acid tries its best to kill off as many harmful microbes as possible and to degrade any harmful chemicals that has made its way in within our food. This first stab at our enemies happens just before the food enters our small intestine. Our small intestine is where most of the absorption of food, or indeed the absorption of any leftover harmful molecules, takes place. So, the stomach prepares the food to enter our small intestine by essentially “cleaning” it of as many toxic substances as possible.

As amylase continues its work, our blood becomes flooded with glucose, which provides us with the energy that allows us to flick the remote control to a new channel as we eat away at our boredom through bag after bag of potato chips on a sad, wintery Saturday night. While some of the glucose will, as we know, be stored as glycogen (thanks to our insulin), the remaining free glucose enters our cells. Here, it is further transformed to produce a form of glucose that is trapped in the cell and eventually to an energy-giving compound called adenosine triphosphate, or ATP for short. ATP fuels all the energy-sapping processes in our cells and in effect can be viewed as the ultimate molecule that keeps the lights on in our cell factories. So, we really need the starch in our foods, as this is what breaks down to become glucose, which in turn produces ATP and ATP is energy. The energy that we need to stay alive.

The heat we use when we cook our foods and the various environments within our bodies help to break down starch into something we can use and convert ultimately into energy in our cells. We know what happens to starch when we cook it in water at 100°C or less, but what happens when we heat our foods to even higher temperatures, such as when we bake or fry our food, for example?

At higher temperatures, such as when baking, the sugar molecules in our food undergo some more chemical reactions to produce new molecules. These new molecules react chemically with our taste buds and provide a vital dopamine release that makes us go back for more food.

One such reaction is the Maillard reaction. In the Maillard reaction, the sugars in our potatoes, for example, react with the amino acids in the protein molecules (potatoes contain a small amount of protein as well as starch and sugar) to give a pleasing brown color to our baked potatoes. Many flavorful brown compounds, known as melanoidins, emanate from the Maillard reaction. The ideal temperature for the Maillard reaction to take place is about 140°C, although the reaction can and does take place at lower temperatures too. However, as the temperature increases, the Maillard reaction proceeds at a faster rate. We do not really know the nature of all the compounds formed during a Maillard reaction but we do know that those formed from a low-temperature Maillard reaction are different from the compounds formed from a high-temperature reaction and this has a direct influence on the flavor of the food. For me, the flavor of a perfectly fried chip is absolute heaven, so I am voting for the high-temperature Maillard reaction every time.

Caramelization is another reaction that adds flavor to our foods and takes place when we heat our food to a high temperature of just above 150°C. You’ll have seen this if you have had crème brûlée at a fancy restaurant. In this reaction, the solid sugar granules melt into a liquid state (with the help of a blow torch), bubbling on top of our dessert, and eventually decompose. The flavor arises from the fact that the sugar molecules are broken down when we apply our blow torch with wild enthusiasm and form volatile (liquid) molecules with that familiar caramel smell. Polymers are also formed from the destruction of the sugars with our handy blow torch and it’s these that impart the rich, dark color we see on caramelization. The actual nature of the brown compounds that give our crème brûlée its warm brown color is still a mystery, however; though we know one thing about them, they are large polymer molecules and do not evaporate to produce a nice smell and their job is to do the coloring-in of the crème brûlée. In the crème brûlée world, every molecule has a job to do, color, smell, taste.

One of my absolute favorite carbohydrates is fried plantain, as the sugar provides the caramelization compounds on high temperature cooking (frying) and the browning gives a light crisp, depending on how much water the plantain contains.

We understand what happens when we heat our carbohydrate sugars and starches, but what happens when we take heat to our proteins? Eating protein is essential, as food proteins are broken down to make the amino acids that in turn make the workhorse proteins that do the heavy lifting in our cells. We also need these amino acids to replenish compounds like dopamine, to make sure that pleasure still has a dominant place in our lives, and to restore compounds like melanin to make sure that sunlight does not have a negative influence on our health.

All food is good and the trick is to get the balance right. Goldilocks knew what she was doing. Things have to be just right.

Unlike the carbohydrates, which unravel from the starch granules, for example, when cooked, sometimes proteins change from a liquid to a more palatable solid, as when we cook egg whites. Remember that in raw egg white, the protein molecules are curled in on themselves. This curled-up state of albumin all changes when we heat the egg white to about 74°C.

With the heating of our eggs in our frying or poaching pan, we broke the hydrogen bonds and then made new van der Waals bonds and disulphide bonds between the albumin molecules. Generally, when we cook proteins, we break weaker bonds, unravel the protein and transform it. Breaking the weaker bonds in our meat creates a protein texture that our teeth find easier to crush as we chew, our esophagus finds easier to despatch downwards by peristaltic waves, and both the pepsin in our stomach and other protein-digesting enzymes in our small intestine find easier to break down.

Pepsin and other protein-destroying enzymes break proteins down by smashing through the amino acid bonds that keep them together. The individual amino acids, or smaller protein fragments, that result from all the enzymatic frenzy in our stomach and intestines are then absorbed. These amino acids are essential as we cannot make them in our bodies and we need the nutritional amino acids to make the new protein workhorses of our cells.

Now let’s turn to cooking fats. Fats and oils are composed of relatively small molecules, which have one distinctive feature, they do not mix with water. If I had managed to cook that wily chicken on the fateful day (I cannot let it go), the fats in the bird’s meat would have softened and the solid fats turned to liquid. Fat molecules become more mobile with heating. You can sometimes see this liquid fat drain out of your roast chicken on to the base of the roasting pan when it’s cooking. If I had attempted to fry our long-lost chicken, the heating of the oil to about 170-200°C during frying would have converted the fatty compounds in the oil from one form of fat, polyunsaturated fat, to another form of fat, the saturated fat variety. All this means is that I would have changed the bonding between the carbon atoms in the fat to a form that is less healthy and more likely to cause disease, such as a clogging of my arteries, eventually.

The frying would also have created some other new chemistries from the fats in both the frying oil and in the chicken. For one, oxidation would have involved the addition of more oxygen atoms to the fats, with the oxygen atoms being harvested from the air. This would have given rise to compounds known as lipid oxidation products. These lipid oxidation compounds are also suspected of being deleterious to health. However, roasting and frying does produce chemical changes that cause the myriad fat molecules to change into more flavorsome entities, and this would have made the chicken more delicious as a result. Frying and roasting also eliminate the water from foods and this is why our roast beef shrinks in the oven, changing from a succulent hunk to a shriveled disappointment after roasting for too long. Frying also increases the fat content of our foods so we consume more fat as a result, which could lead to weight gain.

All these warnings and cautions are all well and good, but it must be emphasized that we need our fat friends. We need fats in our diet as, remember, the fats we eat end up being used by our cellular enzymes to make all the specialized fats that the cells need, such as the soldier fat molecules that encircle all of our cells, for example. All food is good and the trick is to get the balance right. Goldilocks knew what she was doing. Things have to be just right.

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Excerpted from Chain Reaction: How Chemistry Shapes Us and Our World by Ijeoma Uchegbu. Copyright © 2026 by Ijeoma Uchegbu. Reprinted by permission of Mariner Books, an imprint of HarperCollins Publishers. All rights reserved.