The Chemistry of a Barbecue

8th August 2018

Chemistry

Close up of skewers on a barbecue

Rivalling the heat wave of 1976, the UK has been experiencing one of the hottest summers in history. While you may be getting tired of this heat, there is one thing us Brits never get tired of: a good old barbecue! So how does chemistry possibly play a role in this national treasure?

Holy Smokes

It’s not just the cool summer afternoon or chance to sit outside that gets us excited for the first (or twentieth) barbecue of the year. It’s also the thought of that delicious smoky taste you just can’t seem to achieve unless you’re spinning skewers or searing steaks over an outdoor grill.

Like wood, the charcoal used in your barbecue contains several organic polymers like cellulose and lignin. When charcoal burns, it forms a variety of phenolic compounds as a result of the thermal degradation of its organic polymers.

While cellulose is the most famous constituent of wood and charcoal, it is lignin that steals the show here. This is because it is the pyrolysis of lignin that contributes to the irresistible smoky flavour and taste of barbecued meat.

Pyrolysis of Lignin

Lignin is a complex arrangement of phenolic molecules. Not only is it the main constituent of the cell walls in every dry-land plant, it also comes in second place behind cellulose as the most abundant natural polymer in the world.

When lignin burns, it yields a range of aromatic products. The most important of these products are the 2 methoxy-substituted phenols: guaiacol, which causes a smoky flavour, and syringol, which causes a smoky smell.

A black mug on a grill in front of a smoking barbecue

The reason barbecued meat smells and tastes so deliciously smoky is because of the aromatic compounds that are released when the charcoal burns. The most important compounds are guaiacol and syringol.

Guaiacol

With the chemical formula C6H4(OH)(OCH3), guaiacol appears as a yellowish aromatic oil. Also known as 3-methoxyphenol, it can be biosynthesised by a number of organisms and is usually derived from a genus of flowering plants, known as guaiacum, or from wood creosote. Guaiacol can be found in wood smoke as a product of the pyrolysis of lignin.

It is a phenolic compound that comprises up to 85% of the world’s production of vanillin, a fragrant compound and essential component in vanilla. You may also recognise is as a contributor to some of your favourite flavours, including whisky and roasted coffee.

Syringol

Also known as 2,6-dimethoxyphenol, syringol (C8H10O3) is a dimethyl ether of pyrogallol and a naturally occurring aromatic compound. Like guaiacol, it can be found in wood smoke as a characteristic product of the pyrolysis of lignin.

Syringol is responsible for the aroma of most smoked foods, and it is even used in artificial smoke flavourings to give you the experience of a barbecue when the barbecue isn’t there.

How Do These Affect a Barbecue?

Both guaiacol and syringol are characteristic properties of the pyrolysis of lignin. When lignin burns and oxygen breaks it down, these aromatic compounds are released in the form of smoke. They can then stick to the moist surface of the meat being cooked, infusing it with that deliciously smoky flavour.

This is why barbecued meat tastes so good. The presence of charcoal and thereby lignin plays an important role in the production of guaiacol and syringol – but there is another reaction that takes place during barbecuing that is sure to send your taste buds tingling.

The Maillard Reaction in a Barbecue

First discovered in 1912 by Louis-Camille Maillard, this is a chemical reaction between amino acids and reducing sugars that contributes to the tasty flavours of cooked food. It is also one of the only chemical reactions that is better tested in the kitchen than in the lab.

Appropriately named after its discoverer, the Maillard Reaction was initially intended as a cure for diabetes. What it did instead was show why a seared steak, toasted marshmallow, crusty brioche roll and nearly every cooked food tastes so good.

How it Works

In the Maillard Reaction, complex molecules are broken down into smaller pieces. This begins when the heat from your barbecue, grill, pan or even toaster breaks down the proteins in your food. When this happens, amino acids are formed.

Amino acids, particularly lysine and proline, then react with a reducing sugar like glucose. This reaction is what causes the food to brown. This process of browning releases hundreds of potent flavour molecules that all affect the overall aroma and taste of the food being cooked.

The reason it only browns the outside of your food is because the Maillard Reaction only starts when the exterior of the food meets a higher temperature than the inside. This then kick-starts the reaction on the outside of the food. This is also why boiling food, for example, doesn’t have the same flavourful result as, for example, barbecuing food.

A group of people having a barbecue outside

Barbecued foods also get their mouth-watering taste from the Maillard Reaction. This involves amino acids reacting with the sugars in food, causing it to brown and to release a range of flavourful compounds.

The next time you can bring yourself to face the heat and have a barbecue, spare a thought for the complex role that chemistry plays in the irresistible taste of that veggie skewer, juicy burger or chicken drumstick! 

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