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How do archaeologists recover charred plant remains from ancient hearths and middens?

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Archaeology Archaeologists mapping their finds at Pachacamac, Peru, an Indigenous town occupied from approximately 200 bce to 1532 ce, when it was sacked by conquistadors under the command of Francisco Pizarro.

To recover charred plant remains from ancient hearths and middens, archaeologists utilize a technique known as flotation.1

Because charred plant material is typically lightweight and buoyant, researchers place sediment samples from archaeological sites into water. As the sediment is agitated, the charred plant remains float to the surface, allowing them to be easily collected for further study.1

Once recovered, these remains can be identified by genus or species and subjected to various forms of qualitative and quantitative analysis. This process is essential for understanding ancient diets and the origins of agriculture, as charring preserves these otherwise fragile materials in the archaeological record.1

It is important to distinguish this archaeological recovery method from industrial flotation separation, which is a complex process used in mineral processing to concentrate fine-grained ores based on their surface chemical properties.2