Photo: Edinburgh's Museum of Scotland has a number of examples of bog butter on display in its Early People gallery. © Trustees of the National Museums of Scotland.
Chemical experts have examined examples of 2,000-year-old bog butter from the Museum of Scotland to see what our ancestors really used to bury in their peat.
A substance often found in rural Scotland or Ireland, bog butter has regularly been discovered by people digging up peat to burn on their fires.
White in appearance with a texture like paraffin wax, the 'butter' is found in wood or skin containers and has long been thought to be food once buried in the bogs for preservation.
But a team of experts, who recently published their results from a study completed in 2002, look to have deciphered just what bog butter really is.
Speaking to the 24 Hour Museum, Richard Evershed, a Professor of Chemistry at the University of Bristol and member of the team that carried out the research, explained that bog butter has intrigued scientists for some time.
"Chemical analysis was first conducted years ago," he said, "at the turn of the century, then the 1930s and then in the 1970s."
They are, he added, among "the largest deposits of organic material found anywhere in archaeology." But since fat deteriorates in the ground, experts have hitherto been unable to identify exactly what the deposits are.
Local lore has it that the substance is literally the remains of butter and Samuel Butler, a 17th century English writer, once wrote that butter in Ireland was "seven years buried in a bog".
Photo: bog butter has been discovered in various different forms of container from wooden casks to animal skins. © Trustees of the National Museums of Scotland.
However, since the 18th century discovery by French scientists that human corpses often contain a substance known as grave-wax, some have suggested that the waxy deposits could be the remains of carcasses.
The team’s results, published in the Royal Society of Chemistry journal The Analyst, show that bog butter is in fact made up of both dairy and meat product.
Using a method of differentiating between the remains of dairy and meat products developed by Prof Evershed and colleagues in the 1990s, the team examined the fatty acids in bog butter.
They tested artificial examples made in the 1970s from mutton and butter mixed with soil and water and then turned their attentions to nine samples from the Museum of Scotland.
Discovered in various Scottish peat bogs and dating as far back as 2000 years ago, the team found that while six of them were dairy based, the other three were from animal fat. So, the ancient Scots it seems used the nearest peat bog to store both types of food.
But, as Prof Evershed explained, the question still remains as to why they chose to do this. The answer, he said, was probably twofold.
"One is probably because it was preservation," he said. Without the aid of a modern fridge, he added, "how else do you preserve a perishable material?"
The other reason, he explained, could have been an early form of "food processing." Perhaps, "they were actually producing a material that was more palatable," he added.
In order to continue his research Prof Evershed is now planning to carry out further experiments with bog butter in association with the Royal Society of Chemistry by burying modern fatty foods to find out how long the substance takes to form.