Some 30 years ago, archaeologists described sieve-like pottery fragments found in a region of north-central Poland, where some of the region's earliest farmers settled. The shards dated back to between 7,200 and 6,800 years ago. And the holes in the sieves were tiny, just two or three millimeters (about a tenth of an inch) wide.
Alongside the clay fragments were lots of cattle bones, leading some scientists to speculate that the reconstructed bowl-shaped containers were cheese-strainers. But without proof, other hypotheses have endured, including the possibility that the vessels were used to strain chaff while making beer.
In an attempt to figure out once and for all what the containers were for, Salque and colleagues conducted detailed chemical analyses on 50 fragments from 34 vessels. They were looking specifically for residues of fats, which get absorbed by pores in clay during food processing and can remain trapped for millennia.
After crushing a small amount of each fragment into a powder, mixing the powder with solvents, and running the solution through their instruments, the researchers detected milk residues in all but one of the pieces.