Collected from sites along a river in present-day Poland, the pottery pieces are the oldest direct evidence for cheese-making anywhere in the world, the researchers reported Wednesday in the journal Nature. They help paint a picture of the early beginnings of dairying, an agricultural leap that had profound effects on the cultural history of humankind.
With the rise of cheese-making, people of the late Neolithic would have had a rich source of nourishment they could exploit — and store — at a time when most adults would not be able to tolerate lactose, said study coauthor Peter Bogucki, an archaeologist at Princeton University. When curds and whey are separated, the vast majority of the lactose remains in whey, making cheese far more gentle on the gut than is milk.
Bogucki had noticed the hole-studded pottery shards among the more plentiful relics of ancient storage pots during 35 years of excavation work with colleagues in Poland. From bones and other materials, the archaeologists also knew that these early farmers herded cattle in addition to growing crops.
The team did not dwell on the sieve remnants much. Then, in the early 1980s, Bogucki and his wife stopped to visit a friend in Vermont. In the home were 19th century ceramic vessels pierced with holes — and when asked about them, the friend explained they had been used to make cheese.
“It set off a few bells ringing,” Bogucki said.
He went on to formally propose that the ancient hole-studded fragments, which have been found at other Central European sites in addition to those in Poland, were used in the making of cheese. But this was only one of several theories. The vessels might have been used for carrying hot coals, separating honey from honeycombs or in the manufacture of beer.
Now a team led by Richard P. Evershed of the University of Bristol in England has analyzed the sieve fragments and shown they contain milk-fat residues, sewing up the cheese-making theory.
The Nature study, coauthored by scientists from four Polish institutions, is one of several by Evershed's group that uses chemical techniques to probe old pottery for food residues and thus determine what people were eating and how they processed their food.
In 2008, the team reported evidence of milk fats on pieces of pots more than 8,000 years old that were excavated from sites in present-day Turkey, strongly suggestive of cheese-processing.
But although this analysis showed that milk in some form had been stored in the pots, it did not establish for certain that the contents had been cheese. The vessels might have held butter or yogurt or some other lightly processed milk product.
In contrast, finding dairy residue on an implement like a sieve points a powerful finger toward cheese — especially since similar strainers, be they formed from clay or woven into reed baskets, are still in use today in some cultures around the world, said Paul Kindstedt, a cheese scientist at the University of Vermont in Burlington and author of “Cheese and Culture: A History of Cheese and its Place in Western Civilization.”
Evershed's team knew of the European sieve shards and were intrigued by Bogucki's theories about them. So in 2010, PhD student Melanie Salque approached Bogucki and asked whether she could analyze some of the specimens.
Using just a gram of material at a time, Salque first cleaned the pottery to remove any fats on the surface that had come from handling by archaeologists. Then she crushed the pottery into powder, extracted any fats trapped in the clay pores, then used chemical analysis to separate and identify them.
Of 50 pottery fragments derived from 34 separate sieves, about 40% contained fats. In the vast majority of cases, those samples were rich in animal fats, such as palmitic acid and stearic acid, and not in fats from other sources such as plants or beeswax. By measuring carbon isotopes, the team showed that these residues came from milk and not fatty tissue.
As their sophistication grew, farmers would have developed a broader array of cheeses, culminating in the thousands — mild to overwhelming, toothbreakingly hard to buttery-soft — eaten around the world today. But the earliest would have been fairly simple, Kindstedt said.
Without refrigeration, raw milk would have quickly solidified due to fermentation by lactic acid-making bacteria picked up from the teats of cows. Jostled, the mass would have separated into curds and whey and produced a soft cheese akin to quark or fromage frais. Potted, salted and buried in the sand, as some cheeses still are today, it would survive some months without rotting, he said.
Ricotta-like cheeses might have followed: partially fermented milk that is heated till the curds rise to the top and are collected. Rennet cheeses would have come later, he thinks. Coagulated by enzymes in the stomach lining of slaughtered calves, these can be aged for longer and comprise most types of cheese made today.
Cheese, Kindstedt added, would have followed swiftly on the heels of any kind of ancient dairying.
“The first time they stored milk in a pot, I can almost guarantee that if they didn't use that milk immediately, they would come back and it would be a semi-solid gel,” Kindstedt said. “They would be confronted with cheese — it just happens.”
It's gratifying to finally see solid, chemical evidence that the sieves were used for cheese-making, said Oliver Craig, a biomolecular archaeologist at the University of York in England. But to him, it also presents a bit of a mystery.
DNA studies show that genetic mutations giving adults the ability to tolerate lactose swept through the peoples of Europe during the period that the sieves date from. The rapid spread means the mutation must have offered a big advantage to those who carried it.
Presumably, the advantage was being able to digest milk without getting sick. But if cheese-making was well under way, why was lactose a problem?
“Perhaps the sieves were not as effective at removing lactose as we might think,” Craig said. Alternatively, he added, the evolution of lactose tolerance may have occurred elsewhere in Europe among peoples who didn't yet have cheese-making technologies.
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