A baying myriad of hen parties and stag dos greets me as I alight at Faro airport and wipe a film of sweat from my brow. Jacqui's bride tribe and Tony's top staggers rule the roost in the departures queue – uniformed warriors preparing to drink themselves into a stupor under the searing sun. Luckily for my liver, though, I'm not here for a piss-up. I'm visiting Portugal's southern Algarve region for one thing, and one thing only: piri piri chicken.

Known as frango assado in Portugal, piri piri chicken is an Algarvian culinary specialty that involves the brutal candor of spatchcocking a chicken, throwing it on a hot grill, and brushing its tawny flesh with piri piri sauce. Variations of that sauce, as spicy as it is eye-catching in colour, have been kicking around since the 15th century after Portuguese colonists first stumbled upon the chilli pepper while voyaging overseas. Grinding up the piquant pepper and mixing it with a melange of European ingredients (garlic, vinegar, olive oil, salt, bay leaves, lemon juice), those conquistadors created a basic version of the sauce that we still douse our chickens in today.

Whether it's scrawled on menus as piri piri, peri peri or pili pili chicken – all variants of the name for the bird's eye chilli – that peppery dish has almost become as ubiquitous in the UK as fish and chips or pie and mash. One of the latest restaurants in London to experience both commercial and critical success at getting down and dirty with barbecued hunks of chicken breast, thigh and leg is Casa do Frango.

Piri piri heat chart

Portgual's markets are well-stocked with plenty of locally grown piri piri sauce

"My father always said to me, 'If you're going to open a restaurant, make sure it serves chicken,'" says Casa co-founder and Portuguese native Marco Mendes – a man whose intimate knowledge of the Algarve is helping to direct my odyssey in the area. Heeding his father's advice, Mendes opened up Casa do Frango (literally "house of chicken") with his business partner Jake Kasumov in 2018, intent on bringing an authentic taste of Algarvian cuisine to London Bridge. Like its name suggests, the concept at Casa is simple – almost painfully so – but it works. Casa serves a menu where the entire mains section is comprised of one item ("half-chicken brushed with piri-piri") alongside a dozen small plates and sides. It's a straightforward approach to cooking that Mendes has no qualms admitting he cribbed from the grilled chicken restaurants dotted across the Algarve. The very same restaurants that Mendes and his family would frequent on an quasi-religious basis in his youth, and the same restaurants we're hitting up on this whirlwind tour.

Following a quick adjustment to the climate that involves putting on as much sun cream and taking off as many layers of clothing as is socially acceptable, we begin our fowl adventure. Our first poultry pit-stop of the weekend is O Teodósio – an imposing restaurant located in the sleepy parish of Guia. Guia is generally considered to be the place to get piri piri chicken in Portugal. So much so that you'll regularly hear the dish referred to throughout the country as "Frango da Guia". As one of the most popular purveyors in the area of that barbecued bird, O Teodósio proudly calls itself "Rei Dos Frangos" ("The King of Chickens"): a statement you'll find emblazoned on every plate at the premises. Step inside and it's not hard to see why that hubris exists.

The industrial-sized chicken shop, complete with two floors of devastating efficiency where every plastic seat is packed with punters young and old, runs like a well chilli-oiled machine. Everything from the paper tablecloths draped over the tables to the flat-screen TVs broadcasting live soccer are designed to ensure that not a single free kick is missed and not a second is wasted mopping down piri piri-soaked linen. All I can do is marvel at the slickness of the operation as our order is punched in by the waiter on a walkie talkie-like device. He tells me that O Teodósio first opened up in 1982 and, looking at the blasé look in his eyes as endless plates of chicken and chips hurricane around his head, I'm not convinced it's experienced a slow day of service since.

Spare seats are sparse at this frangoria, as manager Renato Brazão explains. "We have 700 chairs," he says, "and each day we serve around 2,500 customers". The secret to O Teodósio's success is its simplicity: a butchered chicken is placed on the grill, salt is added, and the heat of the charcoal is left to work its magic. It's a heat so intense I fear that my contact lenses might fuse to my eyeballs on entering the kitchen. Those haunted by viral videos of anaemic chickens pumped fat with saline fluid will be pleased to know that the spatchcocked hens at O Teodósio's are a healthy yellow; lean and taut as a troupe of gymnasts.

O Teodósio has made frango assado the exact same way here since the very first day of service and, interestingly enough, piri piri sauce doesn't factor in the cooking process. That sauce is instead siphoned into a small metal container on your table to let you heat up your frango to your own personal spice level. I lather it on liberally before mailing it around the table via the central lazy susan, letting the punchy chilli oil seep into every crack and crag of the chicken's blistered skin. Blessed with a "very big" fridge, Brazão estimates that O Teodósio sells "almost 2,000 chickens a day". To put that into perspective, Casa do Frango sells about 2,000 a week.

It becomes evident to me that piri piri chicken isn't just an affordable and delicious dinner in the Algarve: it's an intrinsic part of the culture

With a whole frango setting you back as little as €14 at O Teodósio, it becomes evident to me that piri piri chicken isn't just an affordable and delicious dinner in the Algarve: it's an intrinsic part of the culture. "Frango piri piri got really popular here around the late 1970s and early 1980s," says Mendes, gesticulating passionately over a glass of Super Bock, "it's a concept influenced by Mozambique and southern Africa, but Portuguese families come here in huge groups just to eat the chicken." Your local churrasqueira is where your family comes on the reg to get their fill of flame-grilled frango and taking your business to another restaurant is viewed about as fondly as switching your sporting loyalties from Benfica to Sporting Lisbon. In the Algarve, where you choose between O Ribeirinho, Ramires or O Teodósio (the "big three" according to Mendes) doesn't just indicate where you like to eat, it says a lot about who you are as a person.

There's a beauty in the endless quest for perfection that wills a restaurant to devote itself to perfecting a single dish. Much like the soba shops in Tokyo that won't even consider serving customers until they're content they've created the ideal broth, Ramires and O Teodósio have got grilling poultry down to a fine art. But, as good as it may be, chicken is far from the only foodstuff I sample in the Algarve. We tend to start most days in Faro by making a visit to a nearby pastry shop, filling ourselves with enough pasté​is de nata and travesseiros (a warm and slightly savoury hot pocket of pastry that oozes with a sweet, molten egg custard) to keep us going till lunch. Not only suitable for bleary-eyed breakfasts but bleary-eyed nights as well, a number of these bakeries sell contraband natas out of their back doors in the early hours of the morning. While they aren't technically allowed to sell food at this time due to licensing restrictions, a blind eye is often turned to the practice, much to the delight of the hordes of hungry clubbers tottering back home. That Portuguese passion for pastries is something Casa do Frango hopes to replicate in its new Shoreditch site; a two-storey premises set to open in December complete with an open-plan bakery shilling those fresh custard tarts.

Sugar fix acquired, we soon find ourselves in the neighbouring city of Albufeira, careening down a dusty road to Quinta do Piri-Piri – a chilli farm that we're told holds the key to uncovering the secrets of piri piri sauce. While it's home to more than 30 greenhouse species and roughly 10,000 square metres of chilli, Quinta do Piri-Piri is also a home in the literal sense of the word. Quinta do Piri-Piri's owner Romeu Santos runs a guttering company during the winter months but has been growing chilli peppers out of his villa every summer for the last ten years, having successfully turned his garden into a farm and his hobby of growing heat-seeking pepper missiles into a profitable venture. Despite the ever-increasing popularity of the potent sauces Santon sells to local traders and restaurants, his farm remains a family-run operation. "Only two people work here," he laughs, "though sometimes my mother helps out, too!"

We walk through row upon row of traffic light-coloured chillies, taking care not to caress any of the bright bulbs for fear of contaminating our fingers and soldering our eyes shut. Guiding us past gentle jalapeños (a mere 8,000 on the Scoville scale) and rib-tickling habaneros (around 300,000 units) imported from Mexico, Santos directs us to the spicy stars of his farm: the Carolina Reapers. "We call them nuclear chillis," he says with the tender affection of a sadomasochist as he cradles a two-inch sun-yellow pepper in his palm. A hybrid of a habanero and a scorpion pepper, the Carolina Reaper clocks in at around 2.2 million on the Scoville scale. Which is – in layman's terms – absolutely fucking nuts.

Quinta do Piri-Piri
Romeu Santos

Placing even the tiniest shred of that pepper in your mouth, which I do via a cocktail stick, feels like putting out a cigarette on your tongue; a lingering and fierce heat that works its way down your throat and into your gullet. The more affable malagueta is the chilli favoured for piri piri sauce, though both of these peppers thrive in the dry climate of the Algarve. Balmy winds that come in from North Africa sugar dust the region in a layer of sand sourced straight from the Sahara desert and, speaking to Mendes and Santos about the chilli pepper's complicated ancestry, it's hard to ignore the role that the continent of Africa, and the spectre of colonialism, has played in the creation of piri piri sauce.

It was, after all, the Spanish and Portuguese colonies who were first responsible for disseminating chillies and other foodstuff from Mexico and Central America around the globe in the 15th and 16th century. "There was nowhere else in the world that had those little chilli peppers before Columbus's arrival in the Caribbean in 1492," Professor Rebecca Earle, a food historian at the University of Warwick, tells me over the phone. "They didn't even have them in India."

Then-exotic chilli peppers exploded in popularity as a result of how easy they were to grow and became widely used by colonists as a surrogate for black pepper in their cooking. "Chillis were democratising because they allowed anybody who got ahold of some seeds to plant them in a pot and grow them," explains Earle – an ease of access epitomised by Romeu Santos's makeshift piri piri farm. That widespread transfer of various goods, ideas, and technologies by colonists, missionaries and traders is referred to by historians like Earle as the 'Columbian exchange'. "You could argue that Columbian chilli peppers are about the only good consequence of colonialism," says Earle.

Piri piri chicken is, in many ways, edible evidence of the long history of migration. Having brought chillies over from the Americas, Portuguese settlers in Africa found that the peppers flourished in their new home and quickly became a culinary mainstay in countries like Mozambique and Cape Verde. However, despite crossing innumerable seas and borders to get from the Americas to Africa, it's only in relatively recent history that the piri piri chicken we know and love has cemented its status in Portuguese diets. "In terms of chicken and chips, I think that's a fairly recent combination," says Earle. "The industrial developments of the late 19th and 20th century transformed the way in which restaurants could serve food and the speed at which things could be produced."

Piri piri chicken is, in many ways, edible evidence of the long history of migration

Waves of immigration from Mozambique to Portugal in the 1970s helped the frango craze swell and grow as migrants brought their love of the piri piri chilli back with them to Portugal. The movement was also accelerated by the tourism boom the country received from the British Isles during that same time period. "If anything has made this chicken culture grow it would be the English," says Mendes. "After all, what do English people love more than chicken and chips?"

The final chicken shop we visit, the one that Mendes frequented most often during his childhood, is a testament to that British passion for poussin. Plonked on the Estrada da Fonte Santa opposite an identical outlet of the very same chain, Marufos – affectionately referred to as "the chicken shack" – is one of the most popular frangorias in the Algarve.

The first thing that strikes you upon entering Marufos is the wall of heat radiating from the restaurant's massive open grill; a charcoal-fuelled behemoth capable of cooking 144 chickens at the same time. The large-scale rotisserie system has an almost hypnotic effect and means each carcass receives an even burn and matching blackened pockmarks of flavour.

As our ragtag group of chefs, photographers and journalists waltz up to the counter – looking about as out of place as Jeremy Clarkson at an Extinction Rebellion protest – it becomes evident that the man in front of us is quite the opposite of out of place. He has been here before. A lot. His chequered shirt, cross body bag and wraparound sunglasses are the attire of a seasoned frango assado veteran. All he has to do is hold up three of his linguiça-like digits to the man behind the counter to signpost that he's here for a good time and a long time.

An Irish brogue clamours from the table next to us as we take our seats and there's definitely something to be said for how Brits abroad have helped turn piri piri into a worldwide craze. Lots of red-faced Englishmen in polo shirts (myself included) drink their lager and don't even attempt to speak the native language, preferring instead to fumble their way through the menu crammed with as much advertising (B&M Eletrodomésticos! Expressglass! MM Cars!) as possible.

Despite the influx of foreigners, it's the locals that keep these restaurants running and it's still a predominantly Portuguese crowd at Marufos tonight. "I think the whole thing must have as much to do with the kind of social spaces that these restaurants create than they do with the particular food they're serving," posits Professor Earle on the global chicken shop phenomena. As I watch a baby getting spoon fed its first taste of piri piri chicken from across the room, I can't help but agree.

We drink vinho verde, the green wine Portugal is famous for, and its lightly acerbic edge bounces off the charred chicken and punchy piri piri like a DVD screensaver. Unlike O Teodósio, Marufos' chefs coat the chicken in a dry piri piri rub before grilling it. You can tell. However, just like O Teodósio, Marufos proves that keeping things simple can yield some extraordinary results.

Serving plump chicken cooked over wood and charcoal as well as other riffs on Portuguese classics like octopus rice, bacalhau and chickpea fritters, Casa do Frango's head chef Lucien Green is keen to replicate the vibe of chicken shacks like Marufos in London. "We've taken the concept of Marufos – of that skinny chicken done on a single grill – and adapted it," he says as we go halves on a frango in that very chicken shack.

Not content with just replicating the dishes, Casa do Frango is also attempting to improve on the Portuguese originals, primarily through a more rigid sourcing of produce. "The charcoal's actually better in the UK," explains Green, "the free-roaming chickens? They're also better."

Casa uses three-to-four month old chooks that weigh-in at less than a kilo – a bird that's a damn sight smaller than you'll get from most industrial farms. The mass-production models in play at Marufos and O Teodósio that see thousands of definitely-not-free-range poultry slaughtered on a daily basis are certainly a pitfall of piri piri's popularity. Piri piri chicken has become a very global dish but, amid that growth, it's also become a highly industrial one, too.

That industrialisation is something the team at Casa have attempted to tackle head on. It's why the restaurant eschews the use of factory-farmed poultry and sources its chicken direct from Crazy Dan's House of Meat in Basildon. Creating a successful restaurant is, after all, about creating a social space that makes sense in its environment. An exact replica of Marufos or O Teodósio simply wouldn't work in London for a plethora of reasons – a fact I lament on my way out of Portugal, before I'm reminded that I don't need a carbon copy to get my laughing gear around great chicken: London's got its own thriving chicken-shop culture. Our city is stacked with your classic Morley's and Chicken Cottage as well shinier and more polished newcomers like Chick'n Sours and Bird, and those infused with a more Portuguese flavour, like Casa do Frango.

A few days after my return from Faro, I'm sitting at a table at Casa do Frango's London Bridge premises, filament bulbs above my head threatening to start a Newton's cradle. Why? Because I felt it would, in Proustian terms, "help the memory" of the trip "reveal itself" and make a tidy bookend to this piece. And – y'know – I was hungry.

The woman on the table next to me thumbs through her Instagram stories with the precision of a pneumatic piston; a man on the other side of the restaurant has a conversation so loud and obnoxious that the whole room can't help but eavesdrop; a couple behind me play a game of footsie that sporadically judders the bench I'm sat on. Yet, despite all of our differences, we're all here for the exact same thing: delicious chicken. And that's my kind of hen party.