Charred grain chemistry

Exposing plant matter to moderately high temperatures (230°C) for long periods of time (4-24 hours) results in chemical changes that make the remaining organic matter extremely resistant to degradation and microbial attack. This exposure to heat thus preserves the physical shape of the material so that archaeobotanists are able to identify the types of plants that were present at archaeological sites. Cereal grains and pulses are commonly preserved in this way.

Previous work (Fraser et al. 2013  and Styring et al., 2013) suggested that the bulk isotopic chemistry of cereal grains and pulses is minimally affected by charring.

This project combined multiple measurements of six different taxa – bread wheat, einkorn, emmer, hulled barley, lentil and pea – across a range of charring times and temperatures with microscope analysis of the physical changes that occur. This enabled us to obtain a precisely-measured charring offset to accurately reconstruct the original δ13C and δ15N ratios of the ancient crop remains.

This study is described in Nitsch et al. 2015.