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Dr Pepper

Wouldn’t you like to be a Pepper, too? That won’t be happening for aspiring soda-making rivals anytime soon, because another soft drink with a famously secret formula is Dr Pepper, which is made from 23 natural and artificial flavors. Only three people are said to be privy to the recipe, which was invented in 1885 by pharmacist Charles Alderton in Waco, Texas, and is kept locked in a vault in company headquarters in nearby Plano.

The company has gone on the record to deny one common guess at ingredients: There is no prune juice in Dr Pepper.

While we’re at it, other drinkables whose formulas are closely guarded include Frangelico, Angostura bitters, Chartreuse liqueur and the fizzy drink Irn Bru, which The Guardian newspaper called "Scotland’s best kept secret."

Stephen Hilger | Bloomberg via Getty Images