The pie floater is as South Australian as frog cakes, Haigh's and Coopers.

Once the staple of the late night (and often bleary-eyed) reveller, it has forged its place in the state's history and earned a spot with the National Trust as a heritage icon.

So what is it about the sometimes soggy pastry delight that has captivated generations?

It is a question that has been bugging Tanunda local Rhi O'Geraghty, who said her ex-husband had always turned up his nose at the pie and pea soup concoction.

"How did the iconic Adelaide cuisine, the pie floater, happen?"

Curious Adelaide thought reporter and former New South Welshman Nathan Stitt would be best placed to take an unbiased eye to the pie.

What is it?

To our south Aussie readers, feel free to skip this section because we don't want to tell you how to suck ... errr ... pies.

But for those uninitiated few and the rest of the country, put simply a pie floater is a meat pie inverted in pea soup with tomato sauce garnish. Yummy!

Pie floater with the sauce yet to be added. ( YouTube )

Clearly, culinary licence is taken over the degree to which the pie is submerged, and consistency of the soup.

The floater was originally served 'fresh' from a mobile pie cart on the streets of Adelaide.

It is a connection which would ultimately help launch the dish into history.

To this day, most Adelaideans of a certain generation would have an enduring memory of the Balfour's Pie Cart outside the Railway Station on North Terrace in the CBD.

Late night revellers at the North Terrace pie cart in 1974. ( Trove: Australian Women's Weekly )

Walter Marsh from the National Trust of SA conceded the dish must sound odd to outsiders.

"The really unique South Australian creation might sound strange in other parts of the country, but it is really beloved here," he said.

In his weekly newspaper column, ABC Adelaide personality Peter Goers has described pie floater consumption as a rite of passage.

"Pie floaters taste better if you're drunk," he said.

"Some would say you'd have to be drunk to eat one.

"It's always a sobering and moving experience requiring courage."

Phrases like "unique creation", "rite of passage" and "really beloved" reflect the food's historic significance.

The origin of pie

Whether it is an original South Australian creation or an idea borrowed from abroad, there's no question it has become "Adelaide's own".

History tells us pastry-cook James Gibbs emigrated to Adelaide from Scotland in the 1880s and set up one of the original pie carts on the corner of King William and Rundle streets.

He had worked at a brewery by day for six years to pay for his venture.

James Gibbs standing outside an early pie cart. ( thepiecart.com.au )

The sudden popularity of his floaters meant he was able to expand with new carts quickly, prompting other new vendors and competing carts.

Further north, about the same time in the mid-north town of Port Pirie, baker Ern Bradley used a newspaper advertisement to invite movie-goers to "have a good supper" involving "hot pies ... and floaters".

A newspaper advertisement promoting pie floaters as a treat to enjoy after the movies. ( Trove )

Australian food historian Jan O'Connell penned the book A timeline of Australian food.

In it, she suggested the inspiration for the floater likely came from northern England, where pea and pie suppers were a traditional form of "entertainment".

Whether Mr Gibbs or Mr Bradley or someone else was responsible for the curious combination, its popularity on the streets of Adelaide was clear from the start.

Carte Blanche

Despite a love affair that's endured almost 150 years, pie cart numbers actually peaked in the late 1800s with about 13 or so dotted about the city.

But pre World War I, that number started to drop, leaving 10 servicing the city.

During the depression, it was commonplace for dozens of unemployed to converge on the pie carts at closing time, seeking the generosity of pastry cooks willing to give away their unsold pies.

And by 1938, the ongoing decline in cart numbers was being lamented publicly by at least one journalist in the afternoon daily tabloid, The News.

"Hungry citizens will no longer know the warm intimacy of these sheltered canvas retreats ... honest hearts and sturdy stomachs will mourn the passing of these of the floater — and institution apparently peculiar to Adelaide — a hot pie launched on a sea of peas."

It was once the only way to get a cheap meal after hours.

The city's original late night drive-thru, if you will.

Pie carts a thing of the past

But by the late 1950s, just three carts remained and endured, at Norwood Parade, the GPO, and on North Terrace.

And by 2011, all three had vanished from our streets, with the North Terrace cart making way for the tram extension.

While two pie carts do operate temporarily outside Norwood Oval and the casino during football games, the permanent, late night pie cart is a thing of the past.

The nostalgia for the comfort food has inspired, some would say, questionable acts of devotion.

Police believe the thieves were only after the pies. ( Trove )

At least one South Australian has spent time at a pie cart on his wedding day, while a pie floater craving apparently drove a group of starved bandits to commit a daring robbery.

A 1930 report in The Register said two would-be thieves chased a homeward bound pie cart.

Police later said while the piemen assumed the crooks wanted money, they were probably after the pies instead.

And then there has been the connection to local football.

Many a Redlegs supporter has popped out of the Norwood Oval in the city's inner east to nab a floater from the pie cart parked just outside the grounds.

Modern day meat

There is no doubt pie floater numbers have been in decline, but a devotee can still find the traditional fare on some bakery and pub menus.

There are also new interpretations of the icon.

An Adelaide pub has put a modern spin on the iconic pie floater dish. ( ABC News: Nathan Stitt )

Adelaide's King's Head pub on King William Road has been inspired by the original floater served from the early pie carts, but head chef Lachy Cameron has given it a modern twist and flavour profile.

There's no off-cuts in this pie.

Instead the floaters hold braised wagyu beef and the soup is traded for a pea puree.

Mr Cameron reflected on why the pie floater has remained so popular.

"It's a bit different for South Australians," he said.

"I think because it's been here for such a long time, it's a nostalgic thing for a lot of people, it's a bit of a comfort food."

The verdict?

The conflicting claims to the floater's origin story make it difficult to bite down on where the very first floater was served, but it is likely it coincided with the first pie carts being licensed.

Australians' love of the humble pie coupled with the convenience of the pie cart probably fuelled its initial popularity and don't underestimate the role it played during the depression, lining the stomachs of the unemployed.

But its role as the only late night fast food option, uniting drinkers, truckers, cabbies and workers from all walks of life clearly cemented the humble floater in the collective consciousness of the state.

In the words of one Adelaide chef, "it's a labour of love ... that isn't going anywhere soon."