Heat in Cooking: Back to Basics #1

I was wondering today – what is the most basic thing about food, the most overlooked, obvious thing we never think about while cooking? And then it hit me – we never think about what it really means to cook.

Know your heat

Know your heat

According to the Merriam Webster dictionary, “to cook” means “to prepare food for eating, especially by means of heat”. According to the Oxford English dictionary, it means either “to prepare (food or a meal) by mixing, combining, and heating the elements or ingredients” or (with reference to food) “heat or be heated so as to reach an edible state”. Simply put, cooking is the application of heat to food to prepare it for human consumption.

Ergo, the most basic cooking principle to master is the application and effect of heat on different kinds of ingredients. Time to go back to school, people…

When we apply heat to any substance, changes take place at a molecular level. In the context of food, this means changes in color, flavor, texture, aroma, and, of course, nutritional content.

There are different ways in which you can transfer heat to food; each method has a different effect, and produces different results. Mastering these basics is the first step in bettering your cooking skills.

Types of heat transfer

Different kinds of heat transfer

Different kinds of heat transfer

When we put a pan, skillet, or pot on the stove, we are applying heat by conduction. Heat travels –  is conducted – from the flame to the cookware to its contents, from molecule to adjacent molecule. Conduction continues to take place after the heat source has been removed – in other words, cooking continues after you take the pot off the stove.

Overall, conduction is a somewhat slower method of heat transfer because it relies on direct contact. Depending on the material your cookware is crafted from, you can adjust the speed of cooking; metals are good conductors of heat, with some being better than others; glass and ceramics are generally not as effective.

Convection cooking involves applying heat to food via the medium of a liquid or a gas. Bear with me while I explain how a pot of water boils (remember your physics teacher? I do. Groan).

Convection at work

Convection at work

The pot, and the water at the bottom of it, heats up first (through conduction), expands, rises to the top of the pot, cools, then sinks to the bottom again. En route, it transfers heat to the cooler water through which it travels. This continual “circular” movement eventually heats all of the water, and is called a convection current. The same principle applies when air is heated too.

Stirring achieves the same effect.

Yeah, yeah, blah blah blah, but how does this conduction-convection stuff apply to cooking?

Think of that pot of water again, only now stick an egg into it. Convection currents in the water transfer heat to the surface of the egg – and then conduction takes over and transfers heat from there to its interior. Voilà – ve ‘as le boiled œuf.

Some ovens also employ fans to circulate the air heated by their internal electric or gas heating elements, thereby adding the power of convection to that of…

radiation, which is the transfer of heat energy via electromagnetic waves that travel through space (ooooh, freaky!).

Radiant infrared heat

Radiant infrared heat

There are two kinds of radiant energy used in cooking: infrared radiation (such as that emitted by glowing coals, or the red-hot heating element in an electric oven); and microwave radiation. Food or cookware that absorbs radiant energy from these sources are  heated.

If  you’re using infrared radiation to cook, bear in mind that dark, rough surfaces absorb radiant energy better than smooth, light-colored ones – with the single exception of transparent glass.

A potato's best friend

Microwaves: best for foods with high moisture/sugar/fat

Microwave radiation, produced by microwave ovens, transfers energy through high-frequency waves that penetrate foods, causing their molecules to vibrate rapidly and generate heat. Because microwaves directly reach the interior of a food, the cooking process is much faster.

Foods with a high moisture, sugar, or fat content are best suited to microwave cooking because they readily absorb microwaves. The reason we never use metal in a microwave oven is that metal reflects microwaves, and could cause a fire or explosion.

What Effect Does Heat Have on Food?

Depends on what you’re cooking. These are possibly the most important things you will ever learn about cooking, so pay attention! There are just five things to remember, really:

  1. Water Evaporates. All foods contain some water. Heating water causes it to evaporate. The evaporation of water during cooking dries foods.
  2. Fats Melt. Four key facts: Fats do not dissolve in water. Fats melt and liquefy when heated. Oils are fats that remain liquid at room temperature. Fats do not evaporate.
  3. Sugars Caramelize. As sugars cook, they oxidize, turning brown and changing in flavor. Caramelization of the different kinds of sugars in food – and the associated browning – is one of the most important principles we use in everyday cooking.
  4. Proteins Coagulate. When proteins transform from a liquid state to a solid state, it’s called coagulation. Examples: egg whites changing from a clear liquid to a white solid when heated.
  5. Starches Gelatinize. When mixed with a liquid and heated, starch granules swell, thus thickening the liquid.  Examples: Milk thickens when you add flour (starch) to it and heat it.

Cooking techniques

So now you know the different ways in which heat can be transferred to food, and the effect that heat has on different kinds of ingredients. Still with me?

All cooking processes are either dry-heat or moist-heat cooking techniques.

  • Cooking  with steam, water, or any other liquid (except oil) is a moist-heat technique.
  • Cooking in the absence of any of these is considered dry-heat cooking, even if you’re using oil or fat.

Some cooking techniques, such as braising and stewing, may involve a combination of dry-heat and moist-heat methods.

Dry heat cooking typically involves high temperatures, usually above 150°C; baking, roasting, grilling, broiling, deep frying, and pan frying are all examples of dry-heat cooking. Best suited for ingredients that require

Dry-heat is best for tender cuts of meat

Dry-heat: best for tender cuts of meat

short cooking times or dishes that need to be browned.  Dry-heat cooking methods add crispness and concentrate flavors, but do not tenderize foods. Use for:

  • Thin, tender cuts of meat such as chops or steaks
  • Ground meats
  • Most vegetables
  • Most seafood

With the exception of steaming, moist-heat techniques require lower temperatures – up to 100°C, the boiling point of water – and include steaming, poaching, boiling, simmering, and blanching.

Use for:

Moist heat: Good for starches

Moist heat: Good for starches

  • Tender cuts of poultry, such as chicken breasts
  • Starches and pasta
  • Some fruits
  • Most vegetables
  • Most seafood

Combination techniques, including braising and stewing, are best suited for ingredients that require tenderizing with long, slow cooking times. Use for:

  • Large or dense cuts of meat
  • “Hard” vegetables like carrots, onions, artichokes, cabbage, leeks
  • Tough greens
  • Firm fish

As I continue this series, I will try and explain each of these cooking techniques individually. Of course, you could always visit a restaurant. Otherwise, let’s get cookin’!

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4 thoughts on “Heat in Cooking: Back to Basics #1

  1. This is a good series, Suman. For those wanting a video demo of many of these techniques, should try ‘Cooking Coarse’ series by Tedd Mohr on youtube – I found it very structured and informative. Some of it is directly based on Escoffier, but to be fair to Chef Mohr, he clearly mentions that he is doing so.

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