Our love affair with cheese and beer goes back a long way. Almost three millennia, to be precise.
Workers in a salt mine in Austria were already producing blue cheese and beer in a sophisticated way around 2,700 years ago, according to a new study that found evidence - in pieces of excrement.
The scientists made the discovery by analysing samples of human poo found in the heart of the Hallstatt mine in the Austrian Alps.
Their findings were published Wednesday in the journal Current Biology.
The miners "were sophisticated enough to use fermentation intentionally, which surprised me a lot," Frank Maixner, a microbiologist at the Eurac Research Institute in Bolzano, Italy, and lead author of the study, told AFP.
"This is not something I expected even then".
Oldest evidence of food processing
This is the oldest evidence of cheese maturation in Europe. And while the consumption of alcohol is certainly documented elsewhere by even older writings or archaeological evidence, this is the first molecular evidence of beer consumption on the continent at that time.
"It is becoming increasingly clear that... complex food processing and fermentation played an important role in our early culinary history," Kerstin Kowarik of the Natural History Museum in Vienna, a co-author of the study, said in a statement.
The Hallstatt site, a UNESCO World Heritage Site, is a "very special place in the middle of nowhere" that has been used for salt production for more than 3,000 years, Maixner said.
"All the inhabitants worked and lived from the mine".
In order not to have to go out again during the working day, they ate there and even relieved themselves.
The excrement was particularly well preserved in the mine, thanks to a high concentration of salt and a constant temperature of around 8C.
Four samples were analysed by the researchers: one dating from the Bronze Age, two from the Iron Age, and one from the 18th century.
One of them, about 2,700 years old, was found to contain two fungi, Penicillium roqueforti and Saccharomyces cerevisiae, both of which are now known to be used in food processing.
"Initially, they are found in nature. And then humans use these natural strains to domesticate them," Maixner said.
The researchers first determined that these were not simply natural deposits from outside, by studying the strain present.
"We found so much DNA from these fungi, it was amazing. So much, that we were able to reconstruct their genome," he added.
These were then compared with dozens of modern genomes of these two fungi.
Blue cheese was made intentionally
Thanks to their analysis, the researchers were able to determine that the beer and blue cheese were indeed the result of intentional and repeated fermentation, and not just a "fluke".
As these mushrooms were only found in one dung sample, the scientists would like to confirm, with the help of other samples, whether this consumption was a general trend, or whether it was concentrated in certain periods.
The researchers also studied the diet of these humans. It consisted mainly of cereals (wheat, barley, spelt and so on). They also ate some fruit, and got their protein from beans or meat.
Their diet was "balanced," according to Maixner, and "exactly what these miners needed" to fill up on energy.
Diet changes in modern humans
The main difference with today's menus? The degree of processing of the food, which was very low at the time. The miners used whole grains, for example, suggesting the consumption of a kind of porridge - except for the 18th century sample, where the grains appeared ground, suggesting the consumption of bread or biscuits.
Another finding of the study was the composition of the microbiota of these humans, in other words, the set of bacteria present in their bodies.
The microbiota of the four samples studied was very similar to that of modern non-Western populations, which have a more traditional lifestyle.
This suggests "a recent change" in the microbiota of industrialised humans, "probably due to a modern lifestyle and diet, or to medical advances," the study said.
However, "the microbiota is often linked to different types of diseases today," Maixner pointed out.
According to him, determining the precise moment when this "radical change" took place could help to understand what exactly caused it.