. "When fruits such as raspberries are put in contact with metallic tin, no modification appear, but when Sn2+ ions are deposited on crushed raspberries, a purple, turning to black, colour appears, because the complex of anthocyanins with Sn2+ ions shifts a peak in the absorption spectrum toward shorter wavelengths (This, 1995a,b; Belitz & Grosch, 1999)." . . .