Twenty-one out of 55 bottles of “rare” Scotch whiskies tested at a specialist laboratory in Scotland have been discovered to be fake. Conducted at the Scottish Universities Environmental Research Centre (SUERC) in East Kilbride, the tests found the bottles to be “outright fakes or whiskies not distilled in the year declared,” BBC reports.

Whisky broker Rare Whisky 101 (RW101) submitted the samples for testing following concerns of a growing number of fake whisky flooding the secondary market. The bottles were selected at random from auction houses, private collections, and retailers.

Among the bottles identified as fakes were an Ardbeg 1885, and a Thorne’s Heritage early 20th Century blended whisky. RW101 told the BBC that, had they been real, the combined worth of the 21 bottles would be around £635,000 ($802,000).

The laboratory used advanced radiocarbon dating techniques — more commonly used in forensic and archaeological investigations — to find the age of the spirits. “We’ve come across bottles that were meant to be from the 1850s and clearly they weren’t,” Andy Simpson, co-founder of RW101 said. “When they were dated, the liquid was dated to around the 1980s.”

“The exploding demand for rare whisky is inevitably attracting rogue elements to the sector,” David Robertson, RW101’s other co-founder said. “This problem will only grow as prices for rare bottles continue to increase.”

And increasing they have been. The record for the world’s most expensive whisky was broken three times this year, most recently in November when a bottle of 60-year-old Macallan sold at a Christie’s auction in London for £1,200,000 (roughly $1,528,800).