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The steak is on the grill. The spatter is audible. The potatoes? They’re going to take a while, but they’re safely baking in their tin foil suits. Your barbecue is underway.

Cooking meat outdoors while surrounded by friends, family and something sparkling has become a tradition when the warmer days arrive. What you may not realise while you’re fiddling with your tongs is that, in getting those burgers, steaks and kebabs sizzling, your barbecue is actually a fascinating slice of chemistry in action. Here’s why.

Maillard and meat browning

In 1912, the French scientist Louis Camille Maillard discovered a chemical action between certain amino acids and certain sugars when extreme heat is added (in this case, the heat from your barbecue). This explains why meat browns on the top when it is barbecued, creating intense molecules of flavour.

As tasty as this looks when it’s on the grill in the back garden, the Maillard reaction (as it’s officially called) doesn’t mean the meat is fully cooked. Make sure you cook it for long enough so that, when you poke it with a fork, the juice that runs out is clear and doesn’t have a tinge of pink.

The Maillard reaction isn’t restricted to barbecues. It’s why we get golden crusts on our bread and why chips turn that appetising toasty golden colour.

Health experts have one word of caution. When barbecuing food over smoke (which doesn't happen in a conventional oven), it is exposed to something called Polycyclic Aromatic Hydrocarbons (PAHs). We have to be careful where PAHs are concerned as they are carcinogenic chemicals, meaning they could potentially lead to cancer if a person ingests them. A direct link between PAHs and cancer in humans has not yet been proven.

One suggestion is to part-cook the meat before the barbecue so that it isn't exposed to PAHs for too long, rather then cooking raw meat from scratch on your outdoor grill.

Give your joints a rest

You’ll be tempted to tuck straight into that steak when it comes off the grill, but it actually pays to be patient.

Slice into it straight away and the juices containing much of the flavour will be released, going everywhere except your tastebuds. That won’t happen if you rest the meat for around 10 minutes in a warm place.

It’s all to do with the fibres within the meat. To understand what happens, it helps to visualise the fibres as tubes. When you’re grilling one side of a steak, the heat makes the end of those tubes contract, forcing the juice away from the outside of the meat and into the middle. Flip the steak over and that contraction happens again on the other side, meaning all the juice is forced into a thick band at the centre of the meat. This is more moisture than the fibres can comfortably take, so that juice floods out if you slice the steak as soon as it’s off the barbecue.

You really don’t want to lose that juicy flavour, so leave the meat for a while after cooking. In that 10 minute window, the meat fibres will relax again and the juice will be distributed evenly throughout that freshly cooked slab, ready for the plate, burger bun or skewer.

Take it slowly

Nobody wants their cheeseburger driving them to the bathroom at 3am. To avoid that, barbecue food at a low temperature, and for a long time. Not only are you avoiding the risk of food poisoning, you’re also giving your guests a taste sensation.

It’s best to light your barbecue in plenty of time, so that the flames die down and the charcoal turns to a pale grey ash. It’s this ash which creates the perfect conditions to cook your food properly.

Going back to those meat fibres again, a lower temperature means they shrink less, lose less moisture and the meat stays tender. This more patient approach breaks down the the tough connecting tissues in the meat and forms gelatine, which keeps the moisture inside the meat.

If the meat is fatty, cooking it slowly keeps it tender, as this breaks up any proteins and stops it from becoming tough.

When making a meat-heavy meal for the family, keep in mind the NHS diet guidelines, especially if your feast involves a lot of red meat. Their advice is: grill meat rather than fry it (which is good news if you’re using a barbecue), and to cut off any visible skin or fat before cooking. Keep to no more than 70g of red or processed meat a day. You can read the full guidelines .

Cooking food slowly will also expose it to the PAHs mentioned earlier, for longer. To reduce the impact of carcinogens in the meat, try marinating it in beer.

Food chemist Isabel Ferreira from the University of Porto has shown that marinating meat in beer (especially dark beer) before grilling it on the barbecue has reduced the number of PAHs in it by more than 50%.

Should we wrap those spuds in foil?

That depends. If you spud is only for the oven, then no. Our colleagues at suggest a sprinkling of olive oil and salt is all that’s required for a kitchen bake.

But when it comes to the barbecue, you don’t want a baked potato covered in ash, so that foil forms a handy barrier - as well as conducting the heat from the grill straight into your King Edwards so they bake quicker.

So when you’re served a plate of burgers and baked spuds at your bank holiday barbecue, it’s worth chewing over the complex chemical processes which got them there in first place. And don’t forget to add ketchup.

This article was published in May 2019