How Heat Works
How Heat Works
What Is Cooking???
Cooking is the use of heat to produce a safe, edible, tasteful, and digestible product. There are many factors in cooking that change the composition of ingredients. The application of heat affects the texture, nutrition, color, aroma, flavor, and changes protein structure. The amount of change is varied by technique, temperature, and time.
- Texture – the texture of food changes during cooking because of the moisture that is lost. Proteins coagulate and tissues soften. Water molecules in food turn into steam when goes into the air and the fibers become more soluble – altering the texture of what is being cooked.
- Nutrition – All food will start to break down and lose their nutrient value when heat is applied. The amount of nutrient loss is varied by technique, temperature and time. Steaming is the most effective way to blanche vegetables – least amount of damage to the vegetable and they retain nutrients that are not lost in a poaching medium.
- Color – As heat is applied to food, the chemical composition changes, which in turn makes the appearance change. Sugars in food react with heat in what is know as the Maillard Reaction, also referred to as caramelizing. Typically, the longer a food cooks, the more the color will change, usually darken.
- Aroma – While food cooks – especially when cooked over direct heat, the aroma will change.
- Flavor – Using different cooking techniques, combined with ingredients cooked at different stages in their cooking process will result in different flavors and can drastically change the final taste of a composed plate or dish. Take some time and learn how to use different ingredients in stages of a multi-layered cooking process to achieve different and more complex results.
- The Coagulation of Proteins – When food cooks, the proteins inside coagulate, or change from a liquid to solid state. The longer proteins cook, the more firm they become. Because moisture is lost during the coagulation process, proteins will shrink. Following coagulation, proteins will naturally start to break down the collagen and the elastin in meat. Long cooking techniques (braising and stewing) are a great example of this.
At this point, I am going to have to stop and talk about the Maillard Reaction; Browning vs. Caramelization. Are browning and caramelization the same thing? The short answer is NO. The medium length answer is browning requires protein and since fruits and vegetables contain very little to no protein, they are unable to brown, but are able to caramelize due to the sugar molecules breaking down over high heat. And the long answer (and I was going to make this way longer, but I didn't want to dive too too far down the rabbit hole and lose anyone) is...
In 1912, a French chemist named Louis Camille Maillard discovered that there was a reaction between amino acids and sugars in proteins when applied to heat (over 300 degrees - more on that in a minute) that resulted in new flavors and aromas in browned food to develop. As Maillard discovered this reaction, it rightfully bears his name. Lets talk a little more about the Maillard Reaction.
The Maillard Reaction is a reaction that takes place generally under dry heat cooking process conditions and occurs when heat is applied to a protein, causing the tissues to soften and allow for reducing sugars to be released from the DNA and amino acids to be released from the protein. When these two molecules come into contact with each other, they react and form new and more complex chemical flavor compounds and the simple sugars (ribose and glucose are examples of simple sugars in many proteins) breakdown and then something amazing happens. During this reaction process, new bonds are created between the sugars and the amino acids that link together in ring-like structures and reflect light in a way that makes food take on that signature "browned" color and crust. Now back to the temperature thing. In order for this reaction to occur, not only is heat needed, but the temperature of the heat needs to be above 300 degrees... at a minimum. Up around the 320-330 degrees mark is when we starting seeing more noticeable browning. Above the 330 degrees temperature we start seeing rapid breakdown of the sugars, and then when the temperatures exceed 400 degrees, pyrolysis will eventually occur (your food starts to burn). Let's break all of that down a little bit.
- 300-320:330 - noticeable/visual and olfactory reaction occurring
- 330-350 - the "sweet-spot". This is where you are going to get the most even reaction across the surface of the protein.
- 350-400 - The reaction is happening faster and flavors are getting more complex. The flavors developed in this temperature range are going to be more roasty, malted, and are going to be approaching bitter if not careful.
- 400+ You're playing with fire here... No pun intended. Deep, dark flavors and aromas are produced at these temperatures. At this temperature there is more margin for error as the browning may be very uneven with some spots maturing to burnt before other spots have even picked up color. I'm not saying this temperature is off-limits, but does require a bit more attention and skill to ensure even browning and not burning. Also, of note, pyrolysis has been said to be carcinogenic. But remember back in like 2007 there was a smear campaign (by who I don't know) against grilled food, saying the "charring" from the grates of the grill was said to be linked to carcinogenic cancer causing cells. Well, same thing. Same exact thing. But some of us love "bitter". Along with sour and salty, bitter completes my favorite flavors pyramid.
But that's not it.. we're only like halfway into the Maillard Reaction. I keep bringing up dry heat. As I'll further breakdown dry heat cooking process below, dry heat is needed for the Maillard Reaction to take place. This goes back to the temperature... For Maillard to work the temperature needs to be above 300 degrees - and no moisture, obviously. Water, at sea level, boils at 212 degrees, here 198 degrees. Not hot enough for this reaction to occur. Also, excess water and/or moisture will not allow for reaction to happen, again, because of temperature. So if you have ever seen a recipe that tells you to make sure the surface of your protein is patted dry before cooking, this is why. To take it a step further, if you have ever seen a recipe for your Thanksgiving turkey to be left for 24 hours in the refrigerator uncovered before cooking, this is why - so the exterior can dry out and take on the best crust and color that it can during the cooking process.
Now, Caramelization. Caramelization is the breakdown and reaction of sugars from heat. The difference between caramelization and Maillard is that protein needs to be present. If protein is not present the reaction is caramelization - where the present sugars are undergoing thermal decomposition due to the high heat. To sum this up a bit more clearly, fruits and vegetables caramelize because of the lack of the presence of protein (or they appear in such small amounts their impact is nill. So, as the Maillard Reaction leads to browning and Caramelization is only the breakdown of sugar, can we by definition, use the two words interchangeable? NO! Doing that would be a bigger social faux pas than the time in 2010 when David Cameron showed up in China to observe Remembrance Day wearing a red poppy lapel. (I didn't forget.)
That about wraps up the Maillard Reaction and Caramelization in a nutshell. Except for this one last thing... and this is HUGE! If I have ever taken a utensil out of your hands because you're constantly stirring, poking or prodding, this is for you. The Maillard Reaction and Caramelization are chemical reactions that occur, again, when the temperature is right. When you remove the contact from the temperature required, the process stops, only to start again when contact has been re-established and the temperature rises to where it needs to be for the desired reaction to take place. This leads to uneven browning or caramelization!!! Let your food cook - it's chilling out and doing its thing. I know you think it's sticking, and that's because it is. Your food will tell you when its ready to be turned. It will release when that crust has formed/sugars have caramelized... I promise you. And you're flavor will be better by leaps and bounds.! Now lets move on to how heat mixed with cooking process makes this all possible.
How the Transfer of Heat Works –
Cooking is using heat to alter food. There are four ways that heat can be transferred:
- Conduction – The direct physical contact between two items, where heat moves inward throughout the food.
- Induction – A quicker cooking method using magnetic electricity transfer to heat cookware using a circular magnetic current to conduct heat. Aluminum and copper cannot be used because they have no magnetic properties. This is another example of heat being transferred to food through conduction.
- Convection – Heat being distributed by a liquid medium, or air. There are 2 types of convection: natural & mechanical. Natural Convection uses the natural transfer of heat from top to bottom in a circular motion. The liquid at the bottom of the vessel is heated and rises and the cooler liquid at the top falls to the bottom to reheat. Mechanical Convection is an outside convection source such as a fan blowing oven. Fans used in cooking devices heat quicker and circulate air quicker. This helps for an enhanced distribution of heat.
- Radiation (Infrared & Microwave) – this is the transfer of energy through waves. Waves convert into heat when they come in contact with food. Infrared cooking is when elements heat up to a very high temperature and distribute their heat waves. The waves travel at the speed of light in every direction and the food absorbs them. Microwave Radiation is a special piece of equipment that generates invisible waves and cooks the food by exciting the molecules inside the food which creates friction and heat spreads, cooking the food from the inside out.
Cooking Methods –
The transfer of heat can occur in many different forms, producing different results. Cooking methods are further sub classified by the type of heat applied. There are 3 ways you can apply heat.
- Dry Cooking – a dry cooking technique that transfers heat by direct contact of a hot surface, hot air, hot fat, or radiation.
- Moist Cooking – a wet cooking technique where heat is applied through a liquid medium (stock, steam, boiling, poaching, etc.).
- Combination – a cooking technique that employs both dry and moist preparations, using one process to start and the other process to finish.
- Baking– using dry heat to cook food in an enclosed environment. Temperature range is generally up to 375.
- Roasting – almost the same method as baking, but roasting usually takes place on a lifted rack (to allow airflow from all directions, including the bottom), with the item being left uncovered, and at temperatures at 400 degrees or above.
- Sauté – a cooking process using high heat and a minimal amount of fat. Quick cooking.
- Stir-fry – an Asian dry cooking method. Similar to sautéing but a large high wall pan, or wok is used.
- Shallow-fry – the use of fat to transfer heat to food. Uses more fat than sautéing. Shallow-frying is typically a method that uses lower heat and in turn cooking time is longer. The level of fat should come halfway up the sides of the food being cooked.
- Grill – Using a radiant heat to cook food from below on grates. This includes gas, electric, charcoal or wood burning grills. Charcoal and wood-burning grills are a great way to add a smoky flavor to your food.
- Broiling – Similar to grilling. Broiling uses radiant heat from above. Temperatures for broiling are much higher than grilling.
- Poaching (140-180 degrees) – cooking food in a small amount of a liquid medium, such as a court bouillon.
- Simmering (180-205 degrees) – the cooking of food in a larger amount of a liquid, where the food is cooked by the gentle convection of the liquid.
- Low Simmer - done on low heat. Great for stewing or for stocks - processes with long cooking times.
- Simmer - done on medium low heat. Great for thicker soups and stews. Maybe require more occasional stirring.
- Rapid Simmer - done on medium heat. Almost a full boil, but not quite. Great application for when reducing, or using reduction as a means of thickening. Contemporary pan sauces.
- Boiling (212 degrees, sea level) – the cooking of food in a liquid medium where the heat is higher than a poach or a simmer, and there is rapid convection of the liquid throughout the cooking process.
- Blanch – using boiling water to quickly par-cook ingredients to make them easier to eat or work with on another cooking method to finish them.
- Steam – using liquid that has turned into a vapor to cook ingredients in an enclosed environment.
- Deep-fry – food cooked by complete submersion in fat and heat transfer. Foods typically have a coating or breading that shelters the inside from falling out. There is a standard breading technique for deep-frying.
- Braising – a combination cooking method usually for larger cuts of meat. The meat is first browned on all sides, and then a liquid medium is added, generally 2/3 the way up the sides of the pan. The pan is then covered and cooked in the oven on a lower heat for many hours until the large tough muscle is broken down and very tender.
- Stewing – a combination cooking method usually for smaller cuts of tough meat. The meat is first browned on all sides and then a liquid medium is added the entire way up the cooking vessel, covered or uncovered, and cooked on the stove-top, usually on a simmer.
Now that we understand a little bit more about the cooking techniques, I'll break it down a step further with the method for each technique used and the heat method associated with it.
Technique | Medium Used | Heat Method
- Baking | Air | Dry
- Roasting | Air | Dry
- Sauté | Fat | Dry
- Stir-fry | Fat | Dry
- Shallow-fry | Fat | Dry
- Grill | Air | Dry
- Broil | Air | Dry
- Poach | Liquid | Moist
- Simmer | Liquid | Moist
- Boil | Liquid | Moist
- Blanch |Liquid |Moist
- Steam | Steam | Moist
- Deep-fry | Fat | DRY
- Braise | Fat, liquid | Combination
- Stewing | Fat, liquid | Combination
Time to mess you up a little bit. Look 3 lines above this one to Deep-Fry. Notice that it says that it is a DRY cooking technique? That's not a typo! Back to the temperature again... Water boils at a maximum (under regular conditions) at 212 degrees at sea level, 198 degrees here, not making it possible for the temperature to be hot enough for the reaction to occur. Deep-Frying however is done with oil, not water. Also, the most consistent temperature in which to fry, across the board is 350 degrees (remember above that this is the "sweet-spot"). This allows for the reaction to take place as even without a flame, the surrounding temperature of the food that is being submerged in the hot oil is sufficient enough to cause the reaction. Hey, if nothing else, that question + the provided explanation should win you a couple bets the next time you go to your local watering hole!