LONG BEFORE MODERN refrigeration Irish people discovered that storing butter in the bog keeps it fresher for longer. Much longer. A new study has now revealed that the ingenious practice dates back nearly 4,000 years, 1,500 years longer than previously thought.

The bog’s preservative powers are so strong that butter can still be edible after centuries in the ground. This is thanks to the cool, low oxygen and high-acid environment.

When the food finally deteriorates it takes on a hard, yellowish-white, wax-like texture and a cheesy smell. Chunks of these ancient foodstuffs are still often unearthed by turf cutters.

The new study has found that people were storing butter in Irish bogs in the Early Bronze age and there may have been a booming dairy industry at the time.

The practice lasted a staggering 3,500 years, from 1700 BC to, as recently as, the 17th century.

“The widespread occurrence of these enigmatic butter deposits fits with our increasing knowledge of the central importance of dairying in prehistoric northern Europe,” Professor Richard Evershed from the University of Bristol explained.

Four of the five Bronze Age bog butters studied by the researchers came from Offaly, they were found at Ballindown, Drinagh, Esker More and Knockdrin. The fifth was recovered from Clonava in Westmeath.

The earliest dated sample, from Knockdrin, dates from between 1745–1635 BC. It was found associated with bark, which was possibly a wrapping or container.

“Clearly, it is unlikely there was a single reason for the deposition of bog butter over four millennia,” Dr Jessica Smyth from the UCD School of Archaeology said.

“In certain periods they may have been votive deposits, while at other points in time it may have been more about storage and even protection of valuable resources.”

The National Museum of Ireland works with Bord Na Móna to record and retrieve bog butters that are found by chance.

The archaeology branch of the museum, which is on Dublin’s Kildare Street, has a collection of the butters on display to the public.

The findings of the new study are published in the journal Scientific Reports today.