Irn Bru, drunk by Scots for nearly a century, has been included in the prestigious 900-page Oxford Companion to Food.

The fizzy orange-gold drink is ranked alongside caviar, quail and smoked salmon as one of world's great foodstuffs.

Irn Bru is said by the book to be "important for its symbolic value as well as its refreshing qualities", perhaps most notably known as a reviver after a heavy night's drinking.

The beverage is included among dishes considered to have had an "enormous cultural impact" on their countries of origin.

Name change

A spokeswoman for A.G. Barr said the company was thrilled that its product had been recognised as one of the most influential to come out of Scotland.

Inspired by the tradition of tonics and health drinks prepared by herbalists, the drink was called "Iron Brew" until 1947 when legislation made it compulsory to add 0.125g of iron per fluid ounce to any beverage bearing the name.

Smoked salmon is another Scottish delicacy

There was also some doubt about the future legality of calling something a "brew" if it was not brewed in the traditional manner.

It was marketed in Scotland for many years as being "made from girders" containing properties that gave drinkers amazing strength.

Former diplomat Alan Davidson spent 25 years scouring the world for food and drink worth entering in the guide.

Mr Davidson, 67, said he chose to feature Irn Bru in his book because he fell in love with it the first time he tasted it.

"I was first introduced to Irn Bru 15 years ago when I was visiting a friend in Glasgow," said the London-based writer.

"It's one of my favourite drinks and I try and get whenever I can. It has a great colour and favour and I think the story about it having iron in it is really strange and quite puzzling.

'Amused by history'

"The book is going to be published all over the world so I was looking for stories bizarre stories behind different things to make it more interesting so people read it.

"I think people in Asia and America will be very amused by the drink's history."

The drink's popularity has soared in recent years and is exported all over the world to countries like Canada and France.

Other Scottish delicacies to feature in the book include Dundee cake, clootie dumplings, stovies, haggis and Cullen skink.