Bronze Age Irish ‘Bog Butter’ Is Actually Made From Dairy, Study Finds

It previously was not clear whether the strange swampy snack originated from milk or animal fats

A 2,325-year-old bog butter weighing almost 30 pounds, alongside the keg it was found in. National Museum of Ireland

Within Ireland’s peat bogs lurk many archaeological treasures. Everything from centuries-old bodies, to Bronze Age weapons, to a medieval Book of Psalms have been pulled from the country’s mossy wetlands. Among the more ubiquitous artifacts found in Irish bogs is “bog butter”—yellow, waxy globs of fat that were carefully wrapped in wooden containers or animal bladders before being deposited into bogs for reasons that are not entirely clear. Now, as Jennifer Ouellette reports for Ars Technica, a new study has found that Irish bog butters are precisely what they sound like: very, very old butter.

That conclusion “is not as self-evident as one would suppose,” the researchers behind the new study write in Scientific Reports. Previous analyses of bog butters from Scotland found that while some were dairy-based, others were made from animal fat. So the researchers used stable isotope analysis to examine 32 samples of bog butter held at the National Museum of Ireland. This method, according to the study authors, offers the only reliable way to pin down the precise origins of the strange substance; other techniques have been unable to distinguish between milk fats like butter and animal fats like tallow or lard, explains Richard Evershed, study co-author and professor of biogeochemistry at the University of Bristol.

Of the 32 samples, 26 could be positively identified as dairy, offering the “first conclusive evidence of a dairy fat origin for the Irish bog butter tradition,” the study authors write. Another three samples “probably” derived from dairy fat, and the origins of the other three could not be identified.

The researchers also conducted radiocarbon dating on the samples, and found that three dated all the way back to the Bronze Age, including the Early Bronze Age (circa 1700 B.C.). Two other Irish bog butters were recently discovered to be similarly old; taken together, these findings are “extremely significant,” the study authors write, because they push back the known dates of bog butter deposits “by as much as 1500 years.” The date range of the study samples stretched all the way to the 17th century A.D., suggesting that people in Ireland were dropping their butter into bogs for many centuries.

This in turn begs the obvious question: Why? Scholars can’t say for certain, but one theory posits that bogs’ cool, low-oxygen and high acid environments offered a way to preserve foodstuffs that would have otherwise spoiled quickly. It is also possible that chemical reactions in the soil made the fats more palatable, meaning that the bog butter practice was akin to an early form of food processing.

Over time, tastes seem to have changed. When Ben Reade, head of Culinary Research and Development at Nordic Food Lab, created his own bog butter back in 2012, he found the “qualities of this product were too many surprising, causing disgust in some and enjoyment in others. The fat absorbs a considerable amount of flavor from its surroundings, gaining flavor notes which were described primarily as ‘animal’ or ‘gamey,’ ‘moss,’ ‘funky,’ ‘pungent,’ and ‘salami.’”

Another possibility is that the bog butter deposits had a ritual significance; precious items like gold objects, axes and bladed weapons also seem to have been intentionally deposited in Ireland’s bogs. Given the long period of time that the practice was upheld in Ireland, as the study shows, it is likely that more than one of these explanations is correct.

According to the researchers, their analysis of Irish bog butter is also significant because it points to a “well-established dairying economy” in Ireland by the Early Bronze Age. Previous investigations have shown that milk was already being processed in Ireland during the Neolithic period, and it is possible that the practice increased in intensity until, by the Bronze Age, people were producing enough dairy products that they had to figure out what to do with the surplus.

The new study thus offers further evidence to suggest that milk has been an important food source across thousands of years of human history. Mercifully, thanks to the advent of modern refrigeration, today’s delicious dairy products no longer come with “mossy” undertones.

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