The whisky is believed to have been distilled in 1833 and bottled in 1841, so experts believe it to be the oldest Scotch in existence.
They delved into the castle’s archives and used carbon dating technology at the Scottish Universities Environmental Research Centre to determine that the whisky dates back to the 1830s.
A young Queen Victoria is thought to have enjoyed it when she visited Blair Castle with Prince Albert in 1844.
She was a big fan of a drink called Atholl Brose, which featured Scotch whisky and honey, and records show that she consumed it during her stay.
Castle trustee Bertie Troughton was rooting around in the cellar last year when the hidden door caught his eye. He discovered around 40 bottles of the rare whisky, which is thought to have been rebottled in 1932.
Blair Castle is the ancestral home of the Dukes of Atholl. The family sampled the whisky along with Kythe Distillery co-founder Angus MacRaild, an expert in old and rare whiskies.
‘This is a profoundly historic whisky and a remarkable artefact of Scottish distilling that is unlikely to ever be equalled in terms of provenance and preservation,’ said MacRaild.
‘That it has been carefully re-bottled and preserved at natural strength, maintaining the freshness and power of this spirit for nearly two centuries is frankly, astonishing. To taste it myself has been a great privilege.’
MacRaild said it offers ‘clear textural weight’ in the mouth, while the flavour profile features medicinal characteristics, but without any discernible peat smoke.
Whisky Auctioneer has secured 24 bottles of the Scotch, which will go under the hammer from 24 November to 4 December. Each bottle is expected to fetch around £10,000.
‘Offering the world’s oldest scotch whisky at auction is truly a once in a lifetime occurrence. I’m fortunate to be well acquainted with old and rare liquid, as Whisky Auctioneer handles some of the world’s rarest whisky bottlings,’ said head curator Joe Wilson. ‘This, however, is a transcendent discovery that is sure to capture not just the imagination of the whisky industry but also those well beyond.’