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What you need

An onion

A small piece of lumpwood charcoal

Clarified butter or ghee

Long metal tongs

SINCE the Palaeolithic period, people have used smoke to preserve food. It does this thanks to antioxidants that slow the development of microbes and rancid flavours in meat and fish, as well as antimicrobial compounds such as formaldehyde. Yet smoke also imparts a wonderful flavour.

Food can be hot-smoked in the presence of burning wood, which cooks the food at the same time, or cold-smoked, in which smoke is directed to the food in a separate chamber so it remains raw.

When organic matter burns, the main products are carbon dioxide and water. Yet some carbohydrates, proteins and lipids aren’t fully oxidised: instead, they decompose into a range of compounds that create a smoky flavour.

Wood consists of polymers such as cellulose and hemicellulose, which are comprised of chains of sugar molecules. These effectively caramelise when burned, creating sweet and fruity aromas. Lignin, another polymer in wood, is made up of phenolic molecules, which produce a range of aromatic compounds that contribute to the distinctive flavour of smoke, including guaiacol and syringol.

Many other substances are used as fuel for smoke, including corn cobs for smoking bacon in North America, dried sheep dung for smoking meat in Iceland and peat for smoking barley malt to produce Scotch whisky.

In India, cooks use a technique called dhungar to add smokiness to food and it is easy to carry out in a home kitchen. I learned of the method from , a new book by Nik Sharma that includes explanations of scientific concepts used in the kitchen alongside mouth-watering recipes.

The source of the smoke is ghee: butter that has been clarified by evaporating off the water and removing the milk solids, which scorch and produce unpleasant flavours at around 150°C. Sharma uses the technique as a finishing touch for dal makhani, a rich and buttery lentil stew, but you could try it on almost anything. Smoke flavour is contained in both hydrophobic and hydrophilic compounds, so dishes containing oil or fat will capture more of it.

Take half an onion and hollow out the inside so you are left with a bowl shape. Alternatively, use a small metal bowl. Using your long metal tongs, grab a small piece of lumpwood charcoal, around 3 to 5 centimetres long, and hold it over a flame until mostly white.

Place your bowl or onion inside a pot with your food – it will happily sit on top of a stew. This method doesn’t cook the food, so make sure to do that first. Put the charcoal in the onion, then drop a spoonful of ghee onto the charcoal. It will give off a lot of white smoke, so you should do this somewhere well-ventilated, away from smoke detectors, and immediately cover the pot with a lid. Keep it covered for about 5 minutes, then remove the lid and discard the charcoal and onion or bowl safely.

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