The Science Of Grilling – Cooking Craft Meets Science

Great BBQ grilling is indistinguishable from magic.

You can read recipes, watch great chefs in action, talk to experienced cooks, practice relentlessly. But you can never quite achieve perfection.

Which is a good thing as constant learning and practice is both pleasurable and delicious fun.

Grilling engages all the senses:

• Smell: Grilled food smells delicious, including the charcoal wood smoke.
• Sight: Grill marks and a good ‘char’ makes grilled food look great.
• Sound: Don’t you just love the sound of sizzling meat?
• Touch: Who doesn’t love crispy skin and juicy succulent cuts?
• Taste: The taste of grilled food is unique and delicious.

Chefs & grillmasters will tell you that grilling is an art or a craft, but in fact it’s mostly science.

But did you ever want to know the chemistry and physics behind great BBQ grilling?

Here’s what you need to know.

To cook outdoors, you need to transfer heat energy to change the chemistry of food so that it becomes flavourful, tender, juicy, pleasing to the eye, smell terrific, taste delicious, and have a great texture.

You can do that in three common ways on a charcoal grill.

How your charcoal grill works – direct vs indirect charcoal grilling

1. Radiation: heat transfers without touching the food
2. Convection: heat is blown over the food
3. Conduction: heat is in direct contact with the food

Radiation

Simply put, radiation is heat transference by direct exposure to a source of light energy, in particular infrared (IR) energy. It’s how most charcoal grills work their magic. Think of it as putting a sausage on a fork and holding it to the side of, or over, a campfire – that’s radiated cooking. Distance from the energy source is also important – energy dissipates as you move away from the heat source.

You can have direct or indirect radiation cooking with doors down or up. Direct is when you put your steak on the mesh grill directly above the hot flames, and indirect is when you put it to the side of where the flames are, where it may not be quite as hot. Obviously if your BBQ’s doors are properly heat insulated, this will trap the heat creating an efficient oven effect. Doors closed will also lower the amount of charcoal you use. Creating a dark brown sear on a steak takes direct radiation, whilst roasting a whole chicken or leg of lamb is indirect. Of course you can mix and match between the two, alternately searing and roasting to your taste and culinary skills.

Radiant heat delivers more energy than convection heat.

Convection

When heat is carried to the food by a fluid such as air, water, or oil, that’s convection e.g. boiling food in water or deep frying in oil. When you have one cooking bay (our 600 Streetmaster & 600s Grillmaster comes with three!) of your Trailblazer charcoal grill blazing hot, placing mostly cooked food to one side off the direct radiated heat it ensures it will get slowly cooked with a hot convection airflow as you grill the rest of your food. Gas grills and conventional indoor ovens use natural convection airflow to cook, though a ‘convection oven’ uses a fan and extra heat source to force airflow thus cooking food faster – moving warm air transfers more energy that still warm air. Airflow only cooks the outside of the meat – the inside is cooked by conduction as the heat travels through it.

Conduction

Conduction is when energy is transferred to the food by direct contact with the eneregy source. In the case of a charcoal grill this will be the heat of the mesh grill. Heat is transferred to metal mesh of the grill surface, and although the air and the grates may measure the same temperature, the grates store and transmit more energy that the air as the molecules vibrate.

As the surface of the meat or vegetables gets hotter than the interior, the heat transfers to the centre through the moisture and fats. That’s also conduction. That’s why there are pleasing grill marks on your burgers – it’s a good example of conduction. Heat is transferred to the grill mesh and the hot metal brands the food. The same conduction principle applies to a large solid griddle under the food you are cooking.

Mastering the flame … and time

Great grilling depends on three things – managing the coals, the type of meat or vegetables you are cooking, and time. Hamburgers and sausages for instance are best cooked quickly on direct radiated heat. Ribs and roasts on the other hand need more time and use indirect radiated heat.

When it hits the grill, meat goes through a number of complex processes. Raw beef for instance gets its reddish hue from a protein called myoglobin found in slow twitch muscles that are used for long periods of time and require a lot of energy. Myoglobin proteins are very high in these types of muscles because they can provide cows a consistent supply of oxygen. When the meat reaches 140 to 165 °C (280 to 330 °F) the myoglobin begins to oxidize and the beef will turn brown.

Maillard Reaction

Another big transformation happens as you sear your meat – the ‘Maillard reaction’, the chemical reaction between amino acids and sugar reduction that gives browned food its distinctive flavour. (It is named after French chemist Louis Camille Maillard, who first described it in 1912 while attempting to reproduce biological protein synthesis, a core biological process, occurring inside cells, balancing the loss of cellular proteins through the production of new proteins.) When you sear your meat, proteins and sugars within the meat break down.

Grillmasters know this simply as ‘browning’.

About 3,000 to 4,000 new chemical compounds are formed during this process, giving the meat a more complex flavour depending on the chemical constituents in the food, the temperature, the cooking time, and the presence of air. These compounds, in turn, often break down to form yet more flavour compounds.

Flavour scientists have used the Maillard reaction over the years to make artificial flavours. Seared steaks, breads and even toasted marshmallows undergo this reaction. At higher temperatures, caramelisation (the browning of sugars) and subsequently pyrolysis (final breakdown leading to burning) become more pronounced.

Rather dryly Wikipedia describes the process like this:

The reactive carbonyl group of the sugar reacts with the nucleophilic amino group of the amino acid and forms a complex mixture of poorly characterized molecules responsible for a range of aromas and flavors. This process is accelerated in an alkaline environment (e.g., lye applied to darken pretzels; see lye roll), as the amino groups (RNH₃⁺ → RNH₂) are deprotonated, and hence have an increased nucleophilicity. This reaction is the basis for many of the flavoring industry’s recipes. At high temperatures, a probable carcinogen called acrylamide can form.^[5] This can be discouraged by heating at a lower temperature, adding asparaginase, or injecting carbon dioxide.

That’s the science of grilling!

When you grill, the outside temperature is higher than the inside, triggering the Maillard reaction and creating stronger flavours on the surface.

It also explains why ‘brining’ will help you get a better flavour – the meat’s cell fluids are less concentrated than the salt water so water flows out of the meat cells and salt flows in. That’s osmosis. The salt then dissolves the fibre proteins and the meat’s cell fluids become more concentrated, drawing water back in. Also with more salt and water in the cells, when the meat is cooked and water is squeezed out, there is still water left because water was added before cooking.

Note: each muscle cell in meat has filaments made of two proteins: actin and myosin. Individual protein molecules in raw meat are in coils and when meat is heated, the bonds break and the protein molecule unwinds. Heat will also shrink the muscle fibres as water is squeezed out and the protein molecules recombine so a brine will help reduce that.

Grilled meat flavour

It’s not worth getting into too much detail about the fat content of the meat you use, though it is essential in flavour terms. For instance there are around 600 components in the aroma of beef alone.

The flavour of a steak comes mostly from small molecules produced as the meat cooks. Here are some of those molecules and the flavour notes they impart. Next time you eat steak, see if you can pick out some of these flavours.

Not essential for grilling, but interesting to note, is that the flavour-carrying molecules in meat are hydrophobic i.e. repelled by water. Since meat is around 75% water the flavour-carrying molecules dissolve in fat, and when the fat is heated, it melts and lubricated the muscle fibres in meat helping keep it juicy. (The rest is 20% protein and 5% fat & carbohydrates.)

Heat within meat

When you slap your steak on a charcoal grill, BBQ smoker, or in the oven, the vibrating molecules in the hot air transfers some of its energy to the outside of the meat. This ‘excites’ the molecules on the surface and they transfer heat to the molecules inside and so on. This energy slowly passes towards the centre of the meat like a ‘heat wave’.

Water in meat is a good insulator, especially when trapped inside muscle, so it takes time to cook. The heat moves inwards as the meat seeks ‘equilibrium’ (it’s physics!) trying to make the edge to edge temperature the same. So most of the meat is cooked by the meat, not the air around it.

Bones in meat, filled with fat or air, warm more slowly than the rest of the meat. (Heat also cooks corners and points more because it can burn on multiple fronts – that’s why the corners are crunchier in a lasagna or brownie dish.)

When you take the meat off the heat it continues to seek equilibrium and cooking continues as the heat built up on the outer layers continue to be passed towards the centre, even while some heat is escaping into the air and cooling exterior. This is called ‘carryover cooking’.

A steak might rise a couple of degrees because of carryover, but a thick piece of meat like a turkey breast might rise as 10°F or 6°C in about 15 minutes after removing it from the grill. Knowing this is important because 3-6°C (5-10°F) is the difference between moist and dried out turkey, or a medium-rare or medium steak! Use a good digital probe thermometer to compensate and remove thick cut of meat about 3°C (5°F) below your target temperature.

Time vs weight vs thickness

The thickness of the meat is a major factor in how long it takes to get the center to the desired temperature. A thin steak will evidently cook faster than a thick steak. So a five inch thick prime rib that weighs eight pounds (3.6kg) will be done in the same time as a five inch thick prime rib that weighs 12 pounds (5.4kg).

Never trust a recipe that simply says “cook your steak for three minutes per side” without specifying the thickness of the steak!

Good cooking depends on the proper combination of time and heat. The higher the heat, the less time it needs. If you lower the heat, you need more time. But don’t crank your cooking “all the way to 11” (thank you Spinal Tap)!

Some meats demand low and slow.

Note: your kitchen oven has three ways to control heat and time – a thermostat, a timer, and a heat source. But an outdoor grill rarely has a timer or thermostat, just a blazing heat source. That’s why your ‘significant other’ needs to know how much more difficult it is to cook outside…

When is meat ready to eat?

For most meats, there’s no substitute for knowing precisely what temperature the food is to know when it’s safe to eat. The best way to tell if it is time to eat is with an accurate digital thermometer. You can’t tell by poking the meat unless you’re a pro who has cooked the same steaks on the same charcoal grill for years.

A medium-rare steak, for instance, is 54-57°C (130-135°F) in the centre regardless of how thick, how much it weighs, or what temperature it’s cooked at.

To improve your cooking, get a good digital instant-read meat thermometer and a good digital oven thermometer. Cooking without a meat thermometer is like driving without a speedometer.

Cooking times on a charcoal grill

You don’t need anything more than your hand to know if your grill is hot enough to cook. If you can’t hold your hand over the grill for more than two seconds (just not too close!), it is hot, around 250°C or 450°F. If you can last five to six seconds, the grill is about 140°C or 250°F.

Hamburgers need about 4-5 minutes on each side over direct heat, as hot as you want.

Kebabs, 10-12 minutes total, depending on how well done you like the meat.

Hot dogs & sausages, 8 minutes, but you can turn them as often as you want.

Decent sized steaks, 8-14 minutes for medium-rare, 12-18 minutes for medium. Flip once. If your steaks still have a bone in, subtract one minute.

Chicken breasts without the bone are pretty quick but the temperature you use for steaks and burgers will be too high, so here you might want to go indirect if you are also cooking burgers. 8-12 minutes, turning once, and juice will run clear when they are ready.

Chicken legs, with some olive oil on the surface and a rub or salt applied, take 25 minutes on each side using indirect heat.

Ribs are 1.5 to 2 hours over indirect heat. Baste with any tomato-based recipe you like, but only during the last 20 minutes, (unless you know what you are doing).

Always let the meat rest

When processed by heat, meat fibres are compressed burning all the juice in the middle. If you cut the steak immediately after grilling the juice will flow to the plate from the centre of the meat and will lose a lot of its flavour.

If you give the meat 10 minutes ‘rest’ after grilling to stand on a dish under kitchen foil or lid, the fibres will take their original shape and distribute the juice evenly over the whole piece.

It will taste much better this way. Which is the point, isn’t it?