Our Ancestors Preserved Food in 'Bedrock Metates,' Stone Kitchens That Acted Like Current Day Refrigerators

At present, people have a multitude of food processing methods at their disposal. Some choose the method that will give them the most taste, while many prioritize nutrients. But what happened in the past, what did ancient communities go for, is a question many archaeologists want to learn. Recently, a study published in American Antiquity shared some insights regarding this mystery.

For the study, the experts examined manos and metates uncovered from many ancient sites in the Western U.S. A mano was a stone tool that ancestors used to grind and pulverize food items. The hand-held mano combined with the flat metate for food processing. Metates were of two kinds: one was made of stone, while the other was a depression built into a bedrock surface. The latter, which are often called open-air metates, are very common in archaeological sites.

For the study, researchers employed many new techniques to properly analyze the stone tools. The team's objective was to get out the microscopic plant residues, if any, crammed in the cracks and crevices of the artifacts. "People have lived here for time immemorial and have been processing native plants on ground stone tools for a long time too," said archaeobotanist Stefania Wilks, a NHMU research assistant and University of Utah graduate student, stated Phys.org. The study showcased to researchers the plants used by ancient society for medicine and food purposes.

The team especially focused on extracting starch granules from the artifacts. These granules are present in plant cells, and are utilized for storing carbohydrates. The pursuit was not easy, mainly because of the size of these granules. On average, these granules measure a tenth of a millimeter, which implies they are not visible to the naked eye, making the process more complex. Researchers understood that the bedrock metates, because of its open-air arrangement, was possibly impacted by outside elements like air and water, but believed that crevices could still have protected some of their desired granules. "Through their actions of grinding and mashing, people would have forced these starches down deeper into the stone," Wilks explained.

Researchers noted that the bedrock metates appeared in groups. Many of these tools were detected in the uplands of southern Oregon. "We were up there testing to see if the bedrock metate surfaces were actually being used to process plants," Wilks said. If the assertion turned out to be true, then it would indicate that the area was used for much more than hunting by ancient communities. Experts collected plant residues from the metate surface and from deep in the crevices. The surface specimens had no granules, while the ones collected from the crevices had hundreds. This implied that processing was taking place. "It increased our confidence that what we were seeing was direct evidence that different plant species with starchy organs were processed on the metate," Wilks recalled.

Experts then began identifying the plant species of the granules. Several granules were from the carrot family, and some were from wild grasses. The team also detected the lily family in the collection. "Starch analysis is helpful in studying human diets of the past because some plant parts don't preserve in the archaeological record," Wilks said. Hence, focusing on the starch granules will give them a clear idea about the plants involved in ancient diets.