Archaeological Residues and Recipes: Exploratory Testing for Evidence of Maize and Cacao Beverages in Postclassic Vessels from the Valley of Oaxaca, Mexico

As dates of earliest use of Theobroma cacao in ancient Mesoamerica are established, interest is shifting to how cacao was used. One approach is to consider combinations of ingredients—the recipes for ancient cacao use. Beverages made from cacao seeds and maize have a long history in Mesoamerica. We began testing the hypothesis that there is qualitative evidence of this beverage type in the Postclassic archaeological record in a region where such a beverage, tejate, is a culturally significant food today. We looked for evidence of tejate ingredients in residue samples from eight Postclassic and one contemporary vessel from the Valley of Oaxaca, Mexico. Detection of morphologically specific maize phytoliths was accomplished by taxonomic analysis and comparison with a reference collection. Tejate ingredients Pouteria sapota and Quararibea funebris were also processed for phytolith detection. Testing for methylxanthines characteristic of Theobroma species used high-performance liquid chromatography-mass spectrometry. Four vessels were positive for maize phytoliths; three were positive for theobromine; two were positive for both maize and cacao. No diagnostic phytoliths were identified for the other tejate ingredients. Our hypothesis was supported; still, many challenges are present in the search for a deeper understanding of ancient cacao usage in this region of Mesoamerica.