Massively popular Californian fast-food icon In-N-Out Burger sold out of food before its pop-up shop had even opened in Sydney on Wednesday.

Burger devotees lined up outside the Surry Hills location from 6am to get a taste (one burger per person) of the seminal brand’s world-famous food.

But incredibly, even before the store had opened it sold out of food. That’s 300 burgers, gone.

People in the queue were given wristbands and began getting their hands on the nosh by midday.

It was the fourth time an In-N-Out pop-up had appeared in Australia. It happened twice in 2015 in Sydney and also once in Melbourne in 2014.

On all three occasions food swiftly sold out and hundreds missed out on a taste of one of the world’s most revered burger experiences.

So what on Earth makes it so popular in Australia and indeed the world? And will it ever open permanently Down Under?

We spoke to an In-N-Out aficionado from the US to find out.

The quality of keeping people hungry

There are many secrets to the astronomical success of In-N-Out, author of The New York Times bestseller In-N-Out Burger: A Behind The Counter Look At The Fast-Food Chain That Breaks All The Rules Stacy Perman told The New Daily. 

“It boils down to quality. It starts there,” Ms Perman said.

“The quality burgers that are made the same way since they were in 1948 and it grew up in Southern California marketed by word of mouth and it has this ring of authenticity to it that most chains don’t have anymore.

“It’s run by the same family and the family refuse to go public or to franchise it.”

Instagram is full of In-N-Out Burger love. And it looks amazing. Photo: Instagram

Ms Perman pointed out In-N-Out burger treats its customers and workers “very well” and pays its staff a “very high” wage.

“They don’t really advertise, it is a lot of word of mouth,” she said.

“There is a mystique around it and there is so few of them so it’s always an occasion to find one and to go to one that it became a cult.”

With only the same four items on the menu that were on it when the shop opened in 1948, Ms Perman explained how a “secret menu” at In-N-Out – which the owners do not want to make official or market – had added to the brand’s notoriety and aura.

“People felt they were part of this club with the secret menu,” she said.

It’s also significant, she said, that there were 46 states in the US without a store. It’s an event to find one for most Americans and tourists.

With a mere 305 locations around the country, it had only recently expanded out of California to nearby Texas, Nevada, Arizona and Utah. That’s in comparison to the more than 14,300 McDonald’s franchises in the US. She said maintaining quality and character was the main reason for this.

“Again that goes to quality. If you go inside an In-N-Out you’re not going to see a freezer or heating ovens or those red lights,” Ms Perman said.

“They have their own commissaries and they make their own patties and the commissary has to be within a certain radius of each store so they drive them to the store fresh every day.

“You can only have so many commissaries because they have very high standards and the beef has to be fresh.”

Why pop up in Australia?

According to Ms Perman, there are two explanations. One is for legal and copyright reasons.

She said the brand is afraid of imitations, so pop-ups are created around the world allowing In-N-Out to argue it has an established presence and awareness in numerous countries.

The other is for brand awareness, so when tourists come to the US they want to go and see what the hype was all about.

Will it ever open permanently Down Under?

Yes, In-N-Out “can”, Ms Perman said. However if it actually would was another question altogether.

“I think they would probably go and fill the US before they went abroad,” she said. “But that’s not to say never.

Some where happy at the lack of its famous chips. Instead, it served crisps to some in Sydney. Photo: Instagram/@j4y50n

“A big challenge for them is to be very careful how the volume of a rollout affects the uniqueness, character and quality.

“They could open on every corner such is the appetite for them, but would that corrupt who they are?”

The New Daily contacted In-N-Out Burger to ask about possible plans for Australian stores. A response has not yet been received.

But just because it is unlikely to expand internationally, doesn’t mean its reach will wane.

Celebrities and foodie-gods from all around the world fawn over the restaurant.

Gordon Ramsay and Anthony Bourdain are two of its biggest chef advocates, while Miley Cyrus, Adele, Anna Kendrick and Beyonce have all sung the restaurant’s praises.

Anthony Bourdain explains the allure of In-N-Out: