Large-scale chemical manufacturing isn’t the only setting where complex chemical reactions occur. They take place all around you, and when you fire up the barbecue, they’re everywhere.
Brits love an afternoon barbecue in the summer. But you may be shocked to learn what chemical processes are taking place as your burgers cook.
This article delves into the chemistry behind a barbecue.
Key Takeaways:
There are different types of barbecue smoke, each with a different chemical composition
Smoke rings occur when gases dissolve into the meat and bind to the protein myoglobin
Wood chips add to the flavour of meat when heat breaks down a polymer called lignin
The Maillard reaction contributes to the charred look and flavour of cooked meat
In this post:
The Characteristics of Barbecue Smoke
It’s not just the warm 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 can’t seem to achieve unless you’re spinning skewers or searing steaks over an outdoor grill.
But what’s actually going on?
High-quality, fully carbonised charcoal is mostly pure elemental carbon and ash. When this charcoal burns, it yields carbon dioxide and carbon monoxide.
The white smoke you see directly after lighting charcoal is a mix of water vapour and volatile organic compounds. It’s also called “dirty smoke,” and needs to burn away before adding food to the grill.
Translucent smoke (also called blue smoke) indicates that your grill is burning clean. It’s composed of invisible gas vapour and liquid aerosols. This is the optimal time to throw your meat on the grill.
The Science Behind Smoke Rings
If you’re a barbecue enthusiast, you understand the importance of a good smoke ring. This is the red layer of meat just below the surface of an expertly-smoked brisket.
Meat gets its red colour from a protein called myoglobin. When wood burns, it releases nitrogen dioxide and carbon monoxide. These gases dissolve into the moist surface of the meat and chemically bind to the myoglobin, locking in its pink colour.
On the inside of the meat where the gas can’t reach, heat changes the protein structure, turning it brown.
Woods Chips and Lignin Pyrolysis
When you add wood chips to your charcoal fire, the heat breaks down an organic polymer called lignin in the wood. This breakdown (called pyrolysis) contributes to the irresistible smoky flavour and taste of barbecued meat.
Lignin is a complex arrangement of phenolic molecules. It’s a main constituent of the cell walls in dry-land plants and stands as one of the top three most abundant natural polymers in the world (ranking just behind cellulose and chitin). When lignin burns, it yields a range of aromatic compounds.
The most important of these compounds are the two methoxy-substituted phenols: guaiacol, which causes a smoky flavour, and syringol, which causes a smoky smell.
Guaiacol
With the chemical formula (C7H8O2), guaiacol appears as a yellowish aromatic oil.
Also known as 2-methoxyphenol, it can be biosynthesised by a number of organisms and is usually derived from the genus Guaiacum or from wood creosote. Guaiacol can be found in wood smoke as a product of the pyrolysis of lignin.
Guaiacol is a phenolic compound used as the chemical precursor to produce up to 85% of the world’s synthetic vanillin, a fragrant compound and essential component in vanilla. You may also recognise it 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’s even used in artificial smoke flavourings to give you the experience of a barbecue when the weather keeps you indoors.
The Maillard Reaction
While charcoal and lignin play an important role in the production of guaiacol and syringol, there’s another reaction that takes place during a barbecue that’s sure to send your taste buds tingling.
First discovered in 1912 by Louis-Camille Maillard, the Maillard reaction is a chemical reaction between amino acids and reducing sugars that contributes to the tasty flavour and charred colour of cooked food.
It’s also one of the only chemical reactions that’s better tested in the kitchen than in the lab.
How it Works
Amino acids, particularly lysine and proline, react with a reducing sugar like glucose. This reaction is what causes food to brown. This browning process releases hundreds of potent flavour molecules that all affect the overall aroma and taste of the meat being cooked.
The Maillard reaction requires a specific temperature threshold (typically above 140°C) and requires surface moisture to evaporate. As long as water is present on the surface, the meat cannot exceed the boiling point of water (100°C), which is too low for the Maillard reaction to happen.
Once the surface dries out, the temperature spikes past 140°C, and the browning kicks into high gear. This is the reason boiling food doesn’t brown. It’s also why boiling food doesn’t have the same flavourful result.
Conclusion
Ultimately, the delicious magic of a summer barbecue relies on a complex symphony of organic chemistry happening right on your grill grates. The next time you fire up the grill, spare a thought for the chemistry behind a barbecue and how it creates the irresistible taste of that veggie skewer, juicy burger, or chicken drumstick.
