Bundaberg Rum Overproof has been around as for as long as it’s Underproof brother. It is based on the same spirit, and blended to extra strength. So why is it called “Overproof”? Well, back in the early days there were no sophisticated instruments to measure the alcohol content, so there was an ingenious test used to determine the strength of spirits. Ordinary gunpowder was saturated with the spirit. If, when lit, the powder flashed, it was “overproof”. If it did not, it was “underproof”.