A non-destructive method is used to recover starch from kecaopen grooved vessel sherds from the early Bronze Age site of Yanshi Shangcheng (“Shang city at Yanshi”), located in the Yellow River valley of northern China (Shang Dynsaty/Erligang period). A taxonomic method using morphological and morphometric characteristics identifies extracted starch as millets, Job's tears, snakegourd root, and Triticeae grasses, such as wheat and barley. A few starch grains identified as acorn and tuber (such as lily or yam) were also identified. Damaged starch grains from the ancient starch assemblage share similarities with ground modern reference samples. This suggests that grooved vessels were used to mill plant elements and grind foodstuffs, perhaps to dehusk seeds and make flour from dried roots and acorns in the same way that grinding-stones were used in preceding periods. This hypothesis is supported by the form of the kecaopen vessel, the texture of its inner surface, and modern-use analogy. Plant taxa identified from kecaopen scrapings at Yanshi Shangcheng are similar to economically important taxa identified from scrapings of grinding-stones from preceding periods. This suggests a long continuity in plant processing methods and a long tradition of food preparation based on grinding plant elements, such as seeds, roots, tubers, and acorns.