Burgers used to be fast and cheap - the epitome of fast food. But now a different type of patty exported from the US is rapidly expanding across the globe. US burger chain Five Guys International, is "the complete fundamental change" that has taken place with people prepared to pay more and wait longer for a more upmarket burger.So called millennials, the generation that came of age after the 2008 financial crisis, are their core customers. The trend of diners wanting to know where their food comes from, how it was prepared, and the "story" behind it has also helped drive the better burger's rapid expansion. Nonetheless, it's a profitable market, worth some £3.3bn in the UK last year, according to market research firm Mintel.Making sure its overseas burgers taste the same as those in the US is important, he says. "Unless you have consistency there is no brand... you've got to have some confidence that the burger you have in Dubai and Paris is the same as the one you have in California and Miami," he says.