Robin Barr will announce his retirement at the company's AGM
By Gillian Marles
Business reporter, BBC Scotland
The chairman of the drinks firm AG Barr is finally standing down after more than 48 years with the company.
Robin Barr, 71, will formally announce his retirement at the company's AGM.
Mr Barr is one of only two people in the world who knows the secret recipe for the best-selling Irn Bru drink and the two never travel on the same plane.
Once a month the essences for the drink are personally mixed by Robin Barr in a sealed room at the company's headquarters in Cumbernauld.
The 32 different ingredients are combined in a huge vat, which mixes 8,000 litres at a time.
The recipe was discovered by Robin Barr's great grandfather in 1901 and has not changed in 108 years.
Only one other unnamed person shares the secret but the formula has been written down and is stored in a bank vault somewhere in Scotland.
Even after he steps down as chairman, Robin Barr intends to continue his monthly visit to the Cumbernauld plant to mix the recipe.
However he said he would eventually pass on the secret to his daughter, Julie, who is the company secretary, and she will become the mixer.
Barr's soft drink business was founded in 1875 by Robert Barr from Falkirk and a family member has led the company for 135 years. That will end when Robin steps down.
Robin Barr thinks little will change with his departure because the current chief executive, Roger White, has been effectively running the business for the past five years.
Irn Bru is AG Barr's main brand and remains Scotland's most popular fizzy drink with the equivalent of 12 cans of Irn Bru consumed every second.
The company also produces brands such as Tizer, Orangina and Strathmore water.
The fizzy drink sector has been constantly attacked by the health lobby for contributing to ill health.
Robin Barr will pass on the secrets to daughter Julie one day
Robin Barr has little time for this view.
He said: "If people don't want to become obese by drinking full sugar Irn Bru, they should drink the diet product."
The maverick and sometimes irreverent adverts have also brought the company to the attention of the Advertising Standards Authority.
Although the 1970s slogan 'brewed in Scotland, from girders' remains one of the most enduring, others are remembered for the controversy they caused.
Three years ago, Strathclyde Police complained about one advert which they felt glamorised violence but the accusation was dismissed.
The most recent campaign is a spoof of High School Musical, set at the fictional Auchendookit Senior High.
While accepting his company has sometimes sailed close to the wind, Robin Barr said the adverts have to appeal to young customers.
He said: "The consumer tends to look for edgy advertising for Irn Bru and we hope we don't disappoint them."
Robin Barr will stand down as chairman but will retain a role as a non-executive director, and of course will keep the job as chief Irn Bru mixer.