The Irn Bru slogan “Brewed in Scotland from girders” has some truth – Irn bru contains a small percentage of ferric oxide. Coca-Cola takes a lot of pride in being the world’s favorite soft-drink, but it’s got some tough competition in Scotland. More popular than Coke on a local level, and available with your Big Mac at the local McDonald’s, Irn Bru is an inexplicable hit in Glasgow and the surrounding area.