What are the main flavours/aroma compounds of the Scottish soft drink "Irn-Bru" (Iron Brew)?

Those familiar with the Scottish soft drink Irn-Bru may be familiar with the marketing slogan: "made from girders." This is due to the drink’s taste which some describe as having a metallic edge.

The actual recipe remains a secret, however there is a large range of imitation drinks and unbranded "iron brew" flavoured products (e.g. syrups, confectionery, etc.) with the same taste, so the general flavour recipe must be fairly widespread knowledge within the flavouring industry.

I’ve searched but unlike cola-flavoured beverages, whose flavours have been scientifically studied and for which recipes exist, there is no information about the makeup of iron brew.

So does anyone know… what are the flavours or aroma compounds which go into making an iron brew taste?