At Gaggan, voted Asia’s Best Restaurant for four years in a row, the signature dish is called Yogurt Explosion. Visitors to the two Michelin-starred Bangkok restaurant are always taken by surprise when they first see it. The dish consists of an oval shaped dollop of yogurt in a silver spoon.

The magic begins when the yogurt enters your mouth. It turns out that it is not an ordinary blob of yogurt at all, but a little fully formed pillow, with a delicate membrane which bursts on contact with the heat of your mouth. Once the yogurt pillow explodes, it hits your palate with a burst of sweet, sour, spicy and savoury flavours.

For most foreigners, the dish is a marvel of technique (it is made using a molecular cuisine technology called “spherification”) and, of course, the flavours are delicious.

For Indians, however, the dish evokes a very specific taste memory: paapri chaat. This is a street food staple in North India made from deep-fried sheets of flour, yogurt and spicy chutneys. Within the trade, where the name Yogurt Explosion seems a little fancy, Indian chefs simply call it a Paapri Chaat sphere.

Anand invented the dish seven years ago after working with the Adria brothers of El Bulli in Spain and it is now the defining dish of modern Indian cuisine. Most Indian restaurants, where the chef understands the technique of molecular gastronomy, will offer some variation of Gaggan’s dish. And Gaggan himself jokes that the Yogurt Explosion is the dish that made him rich.

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But here’s what I find interesting: the defining dish of modern Indian cuisine is not a variation on some haute cuisine speciality or even, a riff on home cooking.

It is a dish that derives its flavour – and therefore, its power – entirely from the cuisine of India’s streets. You will find the original paapri chaat all over India. And at street corners, you can buy it for only a few rupees.

Two factors have marked the unstoppable rise of Indian street food over the last three decades. The first is that top Indian chefs, all over the world, have rediscovered the wealth of flavours available on the Indian street and have taken these flavours global, winning Michelin stars and rave reviews. Gaggan was one of the pioneers. But now, street food obsesses most Indian chefs.

The second factor is that even as great chefs offer up their own riffs on the food of the streets, the Indian street is rapidly changing the nature of the food it serves. Oh yes, you will still get paapri chaat. But you will also get many dishes – some with Chinese, Italian and American flavours – that have been recently invented.

As, I imagine, is true of most street food all over the world, India’s street food tradition grew out of necessity. India has no grand restaurant tradition. Most people ate at home till the middle of the 20th Century. If they ate out, it was usually because they had no choice. And because vendors paid no rent and had few overheads, street food was always the cheapest option.

Historically, there are two broad street food traditions in India. The first, which is national, covers all cuisines and most dishes. This was cheap food made for migrant labourers and people who wanted quick meals. This tradition continues to flourish all over India and probably accounts for more than half of all of India’s street food.

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But there is a second tradition, one that originated in the North Indian state of Uttar Pradesh (UP). It probably had the same genesis (quick, cheap meals cooked by people who could not afford to own a restaurant and so, set up stalls on street corners), but it quickly developed an identity of its own.

Its distinctive characteristics were that there was always an element of crispness; deep-fried wheat items (as in paapri or round, hollow pooris) usually found their way into it. There were spicy chutneys and yogurt was often used to temper the tang of the chutneys. (For most people, the mix of yogurt and chutney is the real flavour of street food – hence the success of Gaggan’s Yogurt Explosion.)

Enterprising vendors from Uttar Pradesh travelled East and West, taking their street food with them in the early part of the 20th Century. One lot went East, first to Bihar and then to Bengal. In Calcutta, they tinkered with their recipes to add the sourness and chilli-hotness that the local market craved.

Another bunch went to Bombay where they set up stalls on the iconic Chowpatty Beach. Their UP-style dishes were popular but they soon realised that the Gujaratis of Bombay were keener on texture than the good people of UP.

Out of that realisation came Bombay’s greatest dish, bhelpuri, a mixture of puffed rice, crisp vermicelli made from chick pea flour, boiled potatoes, onions, the signature deep-fried wheat puris and at least two chutneys – a sweet-sour version made from dates or tamarind and its hot, spicy counterpart.

The dish was such a hit that an argument still rages over who really invented it. Was it the UP vendors, responding to local demand? Or was it the Gujaratis who picked up the basic flavours of UP-style street food and refined them?

Uttar Pradesh remains the centre of chaat-style street food. Each city has its own distinctive version and even today, in UP’s cities, chaat will be made with any vegetable. It will be lightly battered and fried till it’s crisp before the chutneys and yogurt are added.

The basic tenets of UP chaat have now spread all over India. You can now call anything chaat if you add chutneys and yogurt. There is even a pre-packaged spice mix called chaat masala that captures the flavours of chaat.

But street food in India has now spread beyond chaat. Just as the UP tradition morphed into something else when it went to Calcutta and Bombay, today’s street food combines a variety of origins and influences, all tweaked to cater to popular tastes.

When the Tibetans came to India in the 1960s, they brought their momos (a kind of rustic dim sum) with them. Now, you can buy momos with various spicy sauces (the equivalent of chutneys in the chaat tradition) at street corners. The dosa, a South Indian rice-pancake, spread all over India in the 1970s. Now, roadside vendors throughout North India will make fresh dosas because they are cheap, filling and delicious.

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Current trends suggest that street food is moving into newer territory. Each year, the National Association of Street Vendors organises an annual street food fair in Delhi. Over the last three or four years, the overwhelming trend has been the adoption of the flavours of Indian-Chinese food. These flavours are basically chilli-umami in that they combine chilli sauce, soy sauce and tomato ketchup.

A decade ago, street vendors began offering Hakka Noodles, a dish of noodles stir-fried with chilli and soya with a little shredded cabbage and onion added for texture. (The majority of India’s Chinese are Hakka in origin but this dish was created by Indians in Bombay.)

Now, that so-called Hakka Noodles turns up everywhere. I have had noodle omelettes, noodle sandwiches (Indians love carb-on-carb), noodle dosas (I kid you not) and even noodle pizza (not made entirely from noodles but a pre-packaged pizza base with noodles on top).

Another street food standby is Manchurian, the name given to the most famous dish of Indian-Chinese cuisine. Chicken Manchurian was invented in Bombay in the mid-70s by placing deep fried, battered chicken balls in a gravy comprising Indian flavours (chilli, garlic, ginger, pepper etc.) with the holy trinity of soya-chilli-ketchup that forms the backbone of Indian Chinese cooking. You get everything made Manchurian style on India’s streets, though a particular favourite is Cauliflower Manchurian.

This year, at the street food fair, I was intrigued to note that white bread has now become an essential component of street food. There has been a bread tradition in Indian street food since the 1960s but there was always a logic to it.

Pav bhaji, a Bombay favourite, was created to feed cotton traders who would leave from the old Cotton Exchange late at night and early in the morning after the New York Cotton Prices had come in. The roadside vendor mashed potatoes with the cheapest vegetables of the day, added masala and copious quantities of commercial yellow butter. The resulting buttery mush was served with white bread buns. It was cheap (the butter was the most expensive ingredient) and filled up the hungry traders.

Similarly the vada-pav, consisting of a potato patty, smeared with spicy chutney and put inside a hamburger-like bun became a favourite in the 1970s with commuters on Mumbai’s local trains because it was cheap and packed with carbs that filled up harassed and hungry train-travellers. And the Bombay sandwich, which comprised salad vegetables between two slices of white bread (the flavour was in the chutney that was brushed on to the bread) was also cheap and easy to make.

But now, street food vendors will make a sandwich with the spicy cooked potato mixture that goes into a masala dosa, coat it in batter and deep-fry it. Or they will throw raw eggs on a slice of bread in a wok and as the egg solidifies, will add chutney and ketchup before finishing the dish off with grated processed cheese.

Purists are sniffy about these recent innovations. And to be frank, I would rather eat UP-style chaat than “Hakka Noodles”.

But that’s OK. The point of street food is that it morphs and shape-shifts. If the UP chaat vendors had not been willing to adapt, we would never have got the Calcutta puchka (a hollow wheat puri filled with a thin watery chutney), a classic of the genre. And there would be no bhelpuri in today’s Mumbai.

The early transformations in chaat were based on greater mobility within India as the country integrated. The newer innovations come from internationalisation and the easy availability of such prepacked ingredients as commercial sauces, white bread and processed cheese.

Each generation of street food vendors has its own dishes. These dishes reflect the flavour and tastes of the India they have grown up in. And often, even great chefs can’t better the street versions. Many fancy restaurants offer their takes on the vada pav. None of them is better than the roadside version.

But no doubt, one day, some chef will crack it. And just as his paapri chaat sphere helped make Gaggan Anand one of the world’s greatest chefs, haute cuisine versions of the new food of India’s streets will win a new generation of chefs their own Michelin stars.

From today’s streets come tomorrow’s classics.

A former editor, Vir Sanghvi is a columnist, TV presenter and author of Rude Food