Ancient denizens of what is now Ireland and Scotland buried stashes of so-called “bog butter” in peat bogs, presumably to stave off spoilage. Thanks to the unique chemistry of those bogs, the stashes have survived for thousands of years. Now, scientists at University College Dublin have conducted chemical analysis and radiocarbon dating of several bog butters recovered from archaeological sites in Ireland. They found that the practice was a remarkably long-lived tradition, spanning at least 3,500 years, according to their new paper in Nature: Scientific Reports.
The researchers also uncovered the first conclusive evidence that Irish bog butters are derived from dairy fat as opposed to being meat-based. According to bioarchaeologist Kristina Killgrove, writing in Forbes, “Previous attempts at analyzing bog butter have come up short, because even though the butter is known to have an animal origin, techniques were unable to distinguish between adipose tissue where lipids or fats are stored and milk fats from ruminants like cows and sheep, particularly on an archaeological time-depth.”
There are some 430 recorded stashes of bog butter, according to Benjamin Reade of the Nordic Food Lab, 274 of which were found in Scotland and Ireland. It’s usually found wrapped in some kind of wooden container—buckets, kegs, barrels, etc.—or animal bladders. The bog butter may have been buried as a means of meat preservation, based on a 1995 study demonstrating that meat buried in peat bogs for up to two years had roughly the same levels of bacteria and pathogens as meat stored in a modern freezer. Alternatively, it may have been a kind of primitive food processing.