"In Trang, they say there's fire in the conversation." This, I'm told, is a way of describing the reason why the southern Thai region's dialogue is frenetic, almost confrontational-sounding, especially compared to the longer, more lethargic speech of Bangkok and the north.

They also say that the food here is so hot – that their commitment to piquancy is so unwavering – that when people from Bangkok order in restaurants, they're told they won't be able to handle it. With this in mind, 'baptism of fire' seems like an apt description of my first visit to the region.

The flight from Bangkok to Trang only lasts an hour or so, but it's a journey that takes you from one world to another; from the swarms of tail-lights, high-rises and unending malls of Thailand's capital to a quite different view. Out of the plane window, lush green mountain peaks reach up and punch holes in soft cloud banks, brown rivers full to bursting snake their way through the carpet of forest. It's, somewhat improbably, my first taste of this continent, and there's something about the snapshot that feels emblematically Asiatic; it's a vision of a mythical Asia.

I'm here to undertake a kind of research trip. You might know the restaurant group Rosa's Thai Cafe for pad thai and pumpkin red curry, but behind its 'greatest-hits' menu and familiar shop-fronts is an unerring search for, above all else, authentic recipes and ingredients. This is very much led by its matriarch Saiphin Moore, a native of a rural area near Chiang Mai in the north. Saiphin and her team's travels across the country have yielded a special set of menus in different Rosa's branches, which aim to show off the different undiscovered cuisines of the country. Trang's is reserved for Rosa's Soho, the brand's second restaurant, and is made up of dishes you can't get anywhere else in London; some of which you won't find anywhere outside of southern Thailand.

'Baptism of fire' seems like an apt description of my first visit to the region

Our first stop on our first morning is a local – and I mean really local – roadside restaurant. It might be the morning, but chilli doesn't wait: we dive into khao gaeng (literally meaning 'rice and curry', referring to a mix of dishes familiar to the region, served warm, not hot, and in plentiful portions). We eat pork and quail's eggs, almost candy-sweet pumpkin, catfish stir-fry, chicken and banana curry and more, served with incredibly tannic, bitter salad leaves, and presenting a kind of piquancy that's by no means unbearable, but that I don't usually associate with breakfast. The setup is sparse, the signs and the awnings are wind-, rain- and sun-battered. Papayas bulge on trees in the courtyard and there's a sense, already, that this is heartland food.

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Juddering around the greenery on a minibus named Thai Tornado, I notice there's a reason the rivers look so huge: Trang is experiencing its worst winter for more than four decades, rain pummelling the roads and forcing the rivers to burst their banks. It certainly adds to the otherness of my experience (there's a reason Europeans are referred to as farang in Thailand; its roots are in the word 'foreign', and I should know, being pretty much the only one here). But its destructive power snaps into focus in other parts of the region, where we drive by almost fully submerged houses and roads so flooded that traffic is stopped, and workers load innumerable mopeds onto the backs of pick-up trucks, one at a time, so that they can continue their journeys.

We press on, though, and Thai Tornado navigates the intermittent heavy rain and patches of brilliant sunshine to the outer reaches of the Trang region. We drive on dirt roads with sweeping mountains either side that call to mind The Beach or Jurassic Park, to a place known simply as the Arts for Life Center, where we're due a lesson in the art of noodle making. The centre takes the beguiling form of a collection of hand-built treehouses that sprawl out and up from the canopy of the surrounding forest. A huge spider hangs lazily in a web below the front entrance. There are ten or so people attending to different pots of noodles, doughs and hot oil; Saiphin is happy, excitable, alternately hollering friendly instructions and running from station to station to enquire about the process. She says the methods remind her of her childhood home.

Here, the speciality is a rice noodle known as kanom jeen, traditionally made with fermented rice flour and, in the case of the batch we preside over, an extract from the 'butterfly pea' plant that turns the noodles a brilliant purple. There's a kind of ceremony to it all: the dough is worked with giant sticks, then put into a 60-year old brass mould and forced through the shower-head-like holes in the underside, into a huge pot full of boiling water heated by burning logs. Before we leave, we try the cooked noodles, and we tuck into a sweet and mellow rice salad made with fermented fish sauce called khao yum, which arrives as beautiful, colourful mounds of salads and rice that are swiftly mixed together.

There's more to the Arts for Life Center than the noodles and other sundries made here, though. It stands as a relic of a sometimes forgotten Thailand: one where noodles are made by elbow grease, not factories, and where water buffalo graze half submerged in the abundant rice paddies. The centre's owner wants to teach Thai people about rice, the "crop that drives Thailand", by reconnecting them with its life cycle. His eventual plan is to build homestays around the location, where artists can come and immerse themselves in the culture of rice. They'll grow it; cook with it; they'll even create art with it.

This individual, emotional attachment to food, I learn, is a point of personal pride in Thailand. Here, recipes aren't toyed with; they're passed down from generation to generation, and their intricacies and peculiarities say as much about the part of the country they hail from as a local dialect. For example, as well as the characteristic heat, dishes from Trang tend to contain lots of turmeric – largely unheard of in the north, but used more the closer to southern India you go in Thailand. Saiphin is relentlessly careful about her methods, considering herself "a cook, not a chef"; a steward of the dishes she recreates.

Elsewhere on our road trips across the region in the two and a half days we spend exploring, Wan – a general manager at Rosa's and a Trang native – and her mother Jitt take us to what feels like an exhaustive itinerary of all that Trang's bounty has to offer. We dive into a noodle shop, where a Chinese influence is palpable in rad nar – flat noodles in sweet gravy that come alive when dried chilli, brown sugar and spices are mixed in.

Roadside canteens influenced by northern Thai and Laotian cooking, popular all over the country, serve up som tam – a cold papaya salad that Saiphin explains is normally made with as many bird's eye chillies as the years the recipient has been alive – as well as grilled tilapia with fresh herbs; fiery grilled pork neck and more.

We also go to a huge outdoor food market, where Jitt, Saiphin and her son Richard – whose passion and excitement for Thai cooking precisely matches his mother's, despite having grown up largely in the UK – lead a frenetic charge of ingredient hunting and snacking. It's an electric atmosphere, and we tuck into fried chicken marinated in umami-laden fish sauce; fried coconut dough; sticky-sweet pork skewers and more. Saiphin and Jitt are constantly sampling, discussing and sampling, and Saiphin gets excited and distracted by ingredients: she sees a Thai aubergine and declares her love for eggplant salad, telling us she has to make us a sample back at Jitt's house.

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In a suburb called Huai Yot, we visit Wan's family home. Wan's father, Nam, owns a curry paste factory nearby, and a mixer takes pride of place in the family's garage – a huge, thrumming machine that pulverises the fresh ingredients into a doughy paste. He creates a batch of the vegan red curry paste for us with red chilli, garlic, lemongrass and a host of other fresh ingredients, and Saiphin explains that Rosa's will take 400kg of spice mixes per week to use in the group's flagship curries. Saiphin and Jitt get to work on preparing some classic Trang dishes, as well as some, like laab (a warm salad of minced meat or fish and aromatic herbs and vegetables, usually eaten with lettuce leaves), that are popular all over the country.

Nam sets to work on a yellow mackerel curry – known as kanom jeen nam ya when served with noodles, as is tradition – by simmering coconut milk on one of two huge, gas-powered outdoor stoves in the centre of the garage, next to the mixing machine. This garage setup – for hot food, at least – is common: Thai cooking is almost always aromatic to the point of being pungent, and cooking semi-outdoors means that the strong aromas can dissipate more easily than in a closed kitchen.

Nam drops in a ball of orange curry paste and stirs, tasting a spoonful of the sauce and giving a thumbs-up. Meanwhile, Saiphin and Jeet prepare fish guts curry (gaeng tai pla), a sauce that stings the palate with its saltiness and rich aroma, using Nam's freshly made curry paste. They also prepare whole frogs from the market in red curry paste – a huge amount of it, too – as well as a few side dishes that (just about) take the edge off the heat.

Around Nam and Jeet's family table, eight or nine of us sit down to eat. The fun began in the garage, but here it's elevated as we dig into a medley of dishes that range from merely slightly piquant to relentless, hard-hitting spice. As we eat, washing dinner down with homemade moonshine and Johnnie Walker and soda, the spice takes control. The frogs in red curry paste dish in particular is pain for pleasure – as I start to sweat and tear up, the all-consuming fire gives way to a genuine high as serotonin kicks in; bouts of laughter and a dreamlike haze take over, and the conversation has us laughing almost hysterically at each other's observations, reactions and facial expressions.

Try it in London

Rosa's Thai Cafe's southern menu

Fancy trying out some of Trang's most spectacular dishes for yourself? Get down to Rosa's Thai Cafe's Soho site and try the southern menu, featuring dishes inspired by the region that include spicy orange curry, smoked mackerel yellow curry, and whole seabass with turmeric.

Rosa's Thai Cafe Soho, 48 Dean Street, W1D 5BF; rosasthaicafe.com

Somehow, improbably, Saiphin tells me that Jeet is effusive about my tolerance for Trang-style heat; I'm navigating territory where even Bangkok residents fear to tread, let alone farang. But it's delicious. It's absolutely, unequivocally delicious. It's moreish, too, from the spicy dishes like the som tam to the warm salads, the green beans with sweet and spicy pork and the rad nar. If the punches of heat are the sides of a mountain to be climbed, the flavours they make way for are the view from the top.

I'm getting a first-hand sense of just how much these historic, precise flavours – recipes that act like formulas to be followed, not equations to be played with – mean to Trang's culture. And above all I feel lucky, blessed even, that the most memorable Thai meal I've ever had is around a family table in Trang, from right out of the frying pan. And into the fire...