The world's oldest flour was made from oat some 32,000 years ago, according to a new analysis of a Paleolithic stone tool.
Recovered in 1989 from a cave in southeastern Italy called Grotta Paglicci, in a layer dating to the Gravettian period about 32,000 years ago, the pestle-type stone was used by hunter-gatherers who made intensive use of the cave.
They left behind wall paintings of horses and hands, human burials and distinctive artifacts, as shown by previous research carried out by Arturo Palma di Cesnola and Annamaria Ronchitelli of the University of Siena, in collaboration with the Archaeological Superintendency of Puglia.
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The elongated cobble of sandstone measures about 5 inches long, it's broken at one end and rounded at the other and features longitudinal fissures on its surface.
"On the basis of the functional analysis, this item has been interpreted as a peste-grinder," Marta Mariotti Lippi, a botany professor at the University of Florence, Anna Revedin, of the Italian Institute of Prehistory and Protohistory in Florence, Biancamaria Aranguren of the Archaeology Superintendency of Tuscany and colleagues wrote in in the Proceedings of the National Academy of Sciences.
They noted the rounded end was used to crush seeds, while the stone's flat surface allowed to grind the broken seeds into flour.
Although it was carefully investigated at the time it came to light, the stone tool was recently subjected to new analysis in order to recover possible bits of starch grain still intact.
The sampling method, adopted for the first time in this research, involved wrapping the stone in a plastic film, to preserve it for further analysis. The researchers exposed only three tiny patches and washed them to recovery loosen debris.
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"Overall, about 1,000 starch grains were observed," the researchers wrote.
They included acorns and relatives of millet, but the most plentiful starch grains were those from wild Avena (oat) species.
Previous starch analysis on grinding stones from Bilancino in the Tuscan Mugello Valley, Kostenki 16 at Pokrovsky Valley, Russia and Pavlov VI in the Czech Republic showed plant exploitation was already spread across Europe during the Mid-Upper Paleolithic.
But the finding at the Grotta Paglicci represents the most ancient evidence of the processing of oat.
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The biologists at the University of Florence recorded a great number of swollen and partly gelatinized grains, featuring the physico-chemical changes that occurs after thermal treatments.
"Grinding oat requires a previous drying of the grains to be processed," Anna Revedin told Discovery News.
"Given a climate colder than the current one, the inhabitants of Grotta Paglicci likely used heating to accelerate drying," Revedin said.
She added that heat treatment of oat helps its preservation while improving the flavor and nutritional properties.
"The early modern humans of Grotta Paglicci already had a knowledge that included a multi-step technology and surprising skills in processing food plants," Revedin said.
The early Gravettian inhabitants of the cave are the most ancient population to use a method that involves at least four steps in preparing plants for consumption.
While the stone tool showed the grains were heated and ground, there is no direct evidence for the following steps, which are the mixing of the flour with water and the cooking.
However, the processes can be plausibly hypothesized, the researchers said.
"Rehydration is necessary for cooking and cooking is necessary to make the starch digestible," they said.
According to Stefano Grimaldi, professor at the University of Trento's department of philosophy, history and cultural heritage, the finding has several scientific implication of extraordinary importance.
"It shows that prehistoric people were able to administrate food resources despite the climate variability," Grimaldi told Discovery News "Such food processing also required organization in work tasks, which determines a social role of men and women, young and elder people. Moreover, the ability to generate reserves and surpluses of diversified food is one of the variables that can determine population growth," Grimaldi said.