Infrared spectrograph of the world's oldest wine residues. The blue line is the ancient wine whilst the red line is modern wine. The spectrographs show how much infrared light was absorbed by the samples compared with frequency. The peaks in the lines represent (with wavenumber position): water (3400); terebinth resin (2900); tartaric acid and calcium tartrate (1600, 1400) and clay (1000). Natural tartaric acid is found only in grapes; the resin is a known wine preservative. The residues were found on fragments of 7000-year-old pottery jars found at Hajji Firuz Tepe, Iran. This test, and others needed to provide the final proof, were done at the University of Pennsylvania Museum.