The Thermodynamics of Food And Cooking On An Infrared Grill


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Thermodynamics Of Food And Cooking On An Infrared Grill

 

What if I told you that cooking is all about chemistry and physics? Would you have flashbacks to your third-grade science teacher and have a breakdown? Would you wish that you paid more attention in science class? Or would you be more interested in cooking because now it seems there is more than meets the eye? Cooking on an infrared grill is not as scary as it sounds and in this article, I will break down for you.

When you think about cooking as a little more than just ‘cooking’ it gets far more interesting. Think about cooking as an experiment with a tasty outcome! Here are a few cooking concepts that should know.

What is Cooking?

Firstly we need to break down and understand exactly what cooking is. Foods are made up of water, protein, fat and carbohydrates. Each food type is made up of a different mix of these elements.

The cooking process is the changing of these elements within the food, usually from transferring energy from a heat source to the food. Primarily this cooking process is done for a long enough period of time until the food is at a temperature where is it safe to digest. Secondly, this process is done until the desired flavour, appearance, juiciness, tenderness or peak nutrient levels of the food is achieved.

What Are The Different Cooking Techniques?

Food is made hot when the molecules around it vibrate so fast that their temperature rises. There are three main cooking techniques, each technique transfers heat to food in a different way. The one that you select for your specific food is crucial.

Convection Cooking

Convection cooking is when the heat source is transferred through to the food by a fluid. Think water, oil or air. Imagine cooking a sausage in your kitchen oven where it is surrounded by hot air. This is convection cooking.

Convection cooking is also cooking that same sausage in a deep fryer, and boiling it in a pot of water. Convection cooking would also be if you turned one side of your grill on (leaving the other side off) and placed the food on the off side leaving the food to be cooked by the natural convection air flow from the hot side. You will find that a good portion of gas grills use this method of cooking.

Conventional indoor ovens also use natural convection air flow to cook foods, but a convection oven includes an extra fan and an extra heat source close to the fan and uses a forced air flow to cook foods.

Convection ovens in general cook foods 25 – 30% faster. Think wind chill.. But the complete opposite. This is because moving warm is can transfer more energy than still air can.

In both cases, airflow is only able to cook the exterior of the meat. The interior of the meat is cooked through conduction as the heat travels through.

Conduction Cooking

Conduction cooking is when the heat is transferred to the food by being in direct contact with the heat source. Think cooking that same sausage in the frying pan. The heat from the element is transferred to the frying pan where the molecules vibrate and pass through to the sausage.

As the outer surface of the sausage heats up, heat is transferred through to the centre of the sausage by the fats and moisture in the sausage.

A classic example of what conduction cooking can be found on meat after using a grill. The grill marks are a branding from where the heat has been transferred from the grill grates to the meat.

Radiation Cooking

Radiation cooking is the transfer of heat from direct exposure to an energy source. Think, putting that sausage on a stick and cooking it to the side of a campfire. This method is how a charcoal grill is cooked. 

When cooking indoors with radiation cooking there are two more methods of radiation cooking that can be used:

1. Excitation: This is how a microwave oven works. In short, a microwave uses radio waves to penetrate the food and vibrates the molecules that are inside of the sausage until it gets hot. It does this without heating the air that is around it. This technology is a form of radiation, however, that I am aware of there is not a grill that works with this technology.

2. Induction cooking: Induction cooking is the latest technique to use on stovetops. It is made up of a copper coil that is placed under a cooktop and uses alternating currents to heat a cast iron or steel pot. The pot then transfers the heat to the sausage without the cooktop or space around getting hot. Induction cooking is one of the most efficient ways to convert energy to heat on a cooktop. This method is very easily controlled (with the knob). Unfortunately, this method is limited to steel or cast iron and does not work with copper, glass or aluminium.

What is the Difference Between Heat and Temperature?

Here is an interesting thought. What is hotter to the touch? A pot of water at 100°C, an oven at 100°C or a frying pan at 100°C?

Pop an empty frying pan and a pot full of water in the oven at 100°C, now leave in there for an hour or so. Now if you were to open the oven and place your hand on the frying pan, in the pot of water or just in the oven in general what would be hotter? (Please do not actually try this). However,  If you were to actually try this you would find that the pot of water and the frying pan will be far hotter than the oven itself. This is because of not all surfaces and transfer heat at the same rate.

This is because steel is around 8,000 times denser than air, which conducts heat at around 1/50 of the rate that steel does.   

Water is also denser than air and it also holds more energy than air so it is able to cook faster than air, then oil is able to cook even faster again. You can speed up the process of an oven by adding a fan, however, this is still not going to be as fast as the other methods.

Temperature is measured by taking an average of each atom, where heat is a total of all atoms. Think of this like money. For example, the average wage in Australia is around $78,000, but the total wages are in the trillions of dollars.

Now radiant heat delivers more heat than convection heat. Let’s give you an example.

You have two separate grills. On the first, you turn on the two burners to the right-hand side and leave the left-hand side off. Now pop a steak down on the left-hand side.

Now on the second grill, you want to turn everything on. Place a steak on the grill and compare it to what happens on the first. It will cook much faster than the first grill. If you leave it on for the same amount of time it will also burn to a crisp. This is because the first grill is using convection heat and the second grill is using radiant heat.

Cooking on a charcoal grill is simple. The more charcoal the more heat. You can easily up the cooking temperature by adding more coals to the fire or take away the heat by taking away coals.

When cooking another thing to remember is how far away the food is from the heat source. The closer the food to the heat source the faster the outside will cook. This can be a fine balancing act. To close and you will burn the outside and not cook the inside. On the flipside, if the food is too far away from the heat source you might only just cook the outside and not cook the inside at all.

When is Food Ready to Eat?

Food is deemed safe to eat when the internal temperature has reached a degree where any harmful bacteria in the food has been killed. This temperature varies between different foods. For example, we know that chicken is safe to eat at 75°C and beef is safe to eat at 55°C. It does not matter which cut of the meat you are cooking, how thick or thin it is or the style you cook it. Its all about the temperature. 

The best (and safest) way to tell if your selected meat is safe to eat is to check it with a digital thermometer. Some foods such as ribs or vegetables it is hard to check with a digital thermometer, with these foods you can normally go off the look of the food or the time it has been cooking.  

For some foods such as vegetables, you don’t need to reach a certain temperature for safe eating. With most vegetables, it’s all about finding the perfect texture, flavour and mouthfeel!

How Does Heat Move Within Food?

When you put food in an enclosed vessel like a pellet smoker, an oven or a grill, the hot air inside, which has a lot of vibrating molecules, transfers parts of its energy to the exterior of the meat. The energy that is in the air excites the molecules on the surface of the meat, which then transfers its heat to the molecules close to the inside and so on until the energy is slowly passed through the meat to the centre. Just like a heat wave.

This process can take a little bit of time because meat is around 75% water, and water is a great insulator. Particularly when it is trapped inside muscle mass. Heat moves inwards because of physics. The meat seeks equilibrium to try to make the temperature even the whole way through, so basically, most of the meat is not cooked from the air but by the meat itself.   

Heat also cooks corners and points of meat more because it can attack it from multiple angles. That is why when you bake something in the oven such as pizza or lasagna the corners & edges are much crunchier than the middle.

After meat is removed from the heat source it continues to seek equilibrium and keeps on cooking. This is because the heat that is built up in the outer layers continues to be passed down to the centre, while part is escaping into the air and cooling the exterior of the meat. This is what we call carryover cooking.

During the carryover period, thicker pieces of meat such as a turkey breast can keep rising as much as nearly 6°C. Thinner cuts such as a thick cut steak might only rise slightly and a chicken breast should not rise at all. This information is important because that much change in temperature can make all the difference between having a nice moist turkey and having a completely dried out piece of turkey. Or even worse having a nice perfect rare steak turned into an overcooked, well-done piece, and let’s face it who wants a well-done steak!

Is Thickness More Important Than Weight?

As your meat cooks the temperature slowly rises. The time it takes your meat to get to temperature is dictated by the thickness of your meat. A thin piece of steak is going to cook far faster than a thick cut. Keep this in mind when you are reading recipes that say something along the lines of, ‘cook your roast for 30 minutes per pound’. If you have a piece of meat that is 1 inch thick and 30 pounds it is going to cook much faster than an 8 inch thick piece that is 30 pounds.

Boiling Point Explained

When boiling liquid to heat food there are some important facts to remember. The temperature will keep rising until it hits boiling point. Once it has reached boiling point, it will not get any higher. Even if you turn up the temperature or crank up the fire you will not get the liquid hotter than 100°C.

However, if we have a sauce that is made up of water and olive oil, it will heat until the boiling temperature of the water until all of the water has been boiled off. Once the water has gone it will then raise to the boiling temperature of the oil which is much hotter than the temperature of the water. Depending on which type of oil this can be up to 260°C . However, before it reaches such temperatures it will start to smoke and eventually burst into flames.  

This same process happens in all different aspects of cooking. When you boil a big pot of homemade bbq sauce the temperature will never exceed 100°C. Everything is warmed evenly and no ingredients burn. Providing you stir the sauce and nothing sticks to the bottom. This is how you can cook the starches on the inside of potatoes without burning the outside, opposed to cooking them on a grill where the outside will burn before the inside is cooked.

Steam forms at a much lower temperature than 100°C, as the molecules of the water get hot and try to escape surface as the water quickly heats. That is why you see water vapour escaping a pot of water before it hits boiling temperature. When water boils, the steam coming off can reach temperatures hotter than 100°C, this happens when it comes into contact with the walls of a hot pot or if it is under high pressure. However, food submerged in water will cook faster than food cooked in steam.  This is because underwater food is surrounded by the hot water molecules whereas in steam there is heaps of air mixed through and air does not conduct heat as well as water does.

Meat is made up of around 75% water. It’s kind of like a wet sponge. As it is heated, water on the surface is energized and some escapes in the form of steam. This still happens in an oven even though the temperature might be well over 100°C, the surface will remain at around 100°C as more water steams away. As the hot molecules escape the cooler ones are left behind. This cools the mean until water stops evaporating, this is usually because the surface dries out and a delicious crust or bark is formed.

At a low cooking temperature such as 125°C, the evaporation rate can be so great that the surface and interior of the meat can stick at around  65°C – 75°C and remain there for hours on end. This phenomenon is called ‘the stall’ and is feared by many. This freak of nature will not happen if the oven is at a higher temperature, say 165°C +.

Cooking with ‘the stall’ actually has a few benefits. (Providing you try to forget that it will take the meat longer to cook) 

 

The Benefits of the Stall Are:

1. The meat is held at a temperature where the cats and tissues can liquify, creating a significant juicer and flavoursome piece of meat.

2. It helps create a really tasty bark.

3. It lets the meat heat evenly the whole way through, so you get a piece of meat that is warm on the inside.

4. It also gives the enzymes a chance to tenderize the meat.

Infrared Cooking

Infrared radiation is one of the best methods for delivering high temperatures to food on a grill. A lot of scorching infrared radiation is produced by charcoal grills. This is converted into heat when it strikes food. Pallet and gas grills mainly produce convection heat.

Think of infrared cooking like the sun. The sun radiates very intense infrared waves which travel at great distances at the speed of light until then make contact with solid matter, such as your skin, at which stage it starts warming you. The sun also radiates ultraviolet waves, these waves don’t only cause warmth but also cause sunburn. This basically means that all infrared heat is radiant, but not all radiant heat is infrared.

Recently a number of different gas grills have been showing their superiority because they are using infrared heat, or they boast an infrared sizzle zone or sear burner designed to give off super high temperatures to get a quick, dark sear on the meat. This is mainly an attempt to try and close the gap with the charcoal grill.

An infrared gas grill has a plate of special glass, ceramic or metal to absorb the heat and light from the flame and re-radiates it to the food in infrared.

Infrared heat is transferred to the food faster than convection but is slower than conduction heating. It can brown food more effectively than a conventional grill but no way near as fast as a hot plate or grill.

How Does My Grill Work?

 

Direct Heat Charcoal or Wood: Radiant heat is produced by the wood/ charcoal at the bottom. The grates above absorb the heat and produce conduction heat on the parts of the meat that touches the grill causing the grill marks. The closed lid reflects convection heat back on the meat. The exterior of the food absorbs heat from below and converts it into conduction heat, which moves to the centre of the meat. 

 

Indirect Heat Charcoal or Wood: This method of cooking creates both convection and radiant heat. The grates absorb heat and produce conduction heat on the surface of the food leaving grill marks. The outside absorbs indirect convection heat from all angles and converts it into conduction heat which heats the centre of the food.

 

Lid Off Charcoal or Wood: Radiant heat is produced by the charcoal/wood. The grills grates absorb heat, creating conduction heat on the foods surface creating grill marks. The foods exterior absorbs radiant heat from below. Energy absorbed from below is converted into conduction heat, then moves to the centre of the food.

 

Flat Top: Charcoal/gas produces radiant heat in the fire box. A solid griddle absorbs heat & creates conduction heat foods surface. The bottom of the food absorbs conduction heat & browns where it is in contact with the flat top & heat is conducted upwards towards the food.

 

Direct Heat Gas: The gas burners create radiant heat, which heats the metal drip protector,  ceramic briquettes or lava rocks. They absorb heat and produce both radiant & convection heat. The grates absorb heat then produce conduction heat on the food surface.  The incoming energy is converted to conduction heat and is transferred to the centre of the food. 

 

Indirect Heat Gas: Burners off to the side produce radiant heat that heats metal drip protector bars, lava rocks, or ceramic briquettes. They absorb heat and produce radiant and convection heat. The grates absorb heat and produce conduction heat on the surface of the food. The exterior of the food absorbs indirect convection from all sides. The exterior of the food converts the energy to conduction heat and it moves to the centre of the food.

 

Lid Off Gas: The gas burners produce radiant heat which heats metal drip protector bars, lava rocks, or ceramic briquettes. They then absorb heat & produce both convection & radiant heat. The grates then absorb heat which produces conduction heat on the food’s surface. The foods exterior converts the energy into conduction heat, then, it moves towards the top of the food.

 

Infrared Gas: The gas burners create radiant heat which heats a special plate. The plate absorbs heat, then emits it as radiant heat in the infrared part of the spectrum. Metal grates absorb the heat which then produces conduction heat, which is contacts the food’s surface. The radiant heat is absorbed by the food and it is converted to conduction heat, where it moves into the centre of the food.

Final Thoughts

There was a lot of information in here, hopefully, now you understand a little more about what cooking is and how different cooking methods work. Hopefully, at your next barbecue, you can wow your guests with intelligent conversations breaking down Induction vs conduction cooking, cooking with an infrared convection oven, or why you prefer cooking with ‘xyz’.  What category do you think wood pellet smokers falls into?

I always find it very interesting hearing about other backyard BBQ enthusiasts thoughts and views about their favourite cooking methods, styles and the different ways you clean & maintain your grill. Once issue that I have been faced with on the past is grill mold, which I despise. If you have any thoughts to share about any of these topics I would love to hear form you below!

Happy smoking

Charlie

 

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