Food Science Friday: How Heat Affects Food During Cooking

By Brian Montgomery

Now that we've talked about the three methods of cooking, let's talk about what actually happens to the food when you cook it! All foods of are made up of a combination of protein, carbohydrates, water, fat, plus small amounts of vitamins and minerals. Understanding what happens to each of these things when heated, and how that changes the shape, flavor, texture and color of foods well help you control the process to get the delicious results you want!

Proteins Coagulate

Proteins are complex molecules that are made of various amino acids bonded into long, loose chains. When heated, the chains unfold (denature), and then they can re-bond into a more solid mass. More simply, when cooked, proteins shrink, lose moisture, and become firm. Coagulation actually refers to this process of proteins changing from a liquid (or semi-liquid) state to a solid state.

frying eggs

In most cases, this process begins at around 140 degrees Fahrenheit. Easy-to-recognize examples of this process include egg whites changing from a clear liquid to a white solid, or a piece of meat becoming firmer as you cook it.






Starches Gelatinize

Starches, which are the complex carbohydrates found in grains, potatoes, wheat, rice, corn and other items, undergo a series of interesting changes when heated. When they gelatinize, the molecules absorb water which makes them swell, soften, and clarify. Liquids will visibly thicken. This process happens gradually over a wide range of temperatures (anywhere from 150 to 212 degrees Fahrenheit), depending on the starch itself. Think adding a starch to a sauce or liquid specifically to thicken it. Another example is the flour in a cake batter, which gelatinizes when it absorbs the water from eggs, milk and other ingredients, which makes it partially responsible for the firming and drying of a baked good!

Sugars Caramelize

Heating up sugar past 330 degrees Fahrenheit results in caramel, and not surprisingly, this process is called Caramelization. The same thing happens when you cook onions down for French Onion Soup or make a rich creme brulee. When the sugar is exposed to heat, first it melts, but as the temperature continues to rise, the sugary syrup gradually turns yellow, and then brown, changing not only the color but imparting the rich, delicious flavor.

heating sugar to caramelize it

Add some protein to the mix, like with a steak, and the end result looks similar--the food gets brown and the taste changes, but it's actually a completely different chemical process happening. What is actually taking place is called the Maillard Reaction, which is named after chemist Louis-Camille Maillard, who first described it in 1912.

steaks browning

As you heat the steak, the sugars in the meat start reacting with the amino acids (parts of the protein). The delicious result is a lovely brown color, and all the mouth-watering flavors and aromas we experience when we think of steak. We can all thank the Maillard Reaction for tastiness of coffee, chocolate, baked goods, dark beer (the malted barley), and even roasted meats and nuts!

Water Evaporates

Every food has some amount of water in it, some more than others. For example, up to 75% of raw meat is water! As a food is heated, the water begins to evaporate, resulting in the food drying as it is cooked.

Fat Melts

Fats are used for energy in the plant or animal that stores it. Their textures can range from firm to liquid. For example, oils are just fats that stay as a liquid at room temperature. Fats melt when heated, softening and liquefying. They won't evaporate, and can usually be heated to relatively high temperatures without burning so they are often used to brown or fry foods.

Fats also provide the rich flavor and texture we associate with many of our favorite foods. For example, during baking, fat helps tenderize, leaven, retain moisture, and create a flaky or crumbly texture.

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