Lime treatments for food preparation identified in Postclassic Xochimilco (Mexico) ceramic sherds

Abstract Archaeological ceramics in Mesoamerica sometimes display a whitish layer in the inner part of the vessels, which has been related to the use of lime to obtain alkaline solutions for treating foodstuffs, in particular maize, in a process that is called nixtamalization. In this paper we provide more evidence for this practice, and we also suggest that alkaline solutions might have been used to process other foodstuff. With this aim we have studied ceramic vessels recovered from Postclassic Xochimilco, Central Mexico. We analyzed the white layer through FT-IR to confirm it was made of calcium carbonate, and observed it by binocular microscopy, which allowed us to record the presence of several microlayers, that might have been formed during multiple uses of the vessels. Starch grain analyses were applied to identify residues preserved in these layers and the ceramic surface. The results suggest that the presence of a whitish layer was associated not only to maize, but also to other plant foodstuffs, therefore suggesting that Xochimilcans from the Mexica lordship in pre-Hispanic times were likely applying alkaline treatments to process different plant ingredients. The use of alkaline products to treat food besides maize is common in modern Mexico, but to date, it has not been reported archaeologically.