Laboratory simulations of the transformation of peas as a result of heat treatment: changes of the physical and chemical properties

The residues of heated organic remains, usually called carbonized or charred remains, are ubiquitous in the archaeological record and are often used to interpret certain aspects of past ways of living. This study focuses on the physical and chemical alterations, both as a function of temperature and time that occur when the transformation of a polysaccharide-rich biomass is simulated in the laboratory. Peas (Pisum sativum) are heated at temperatures ranging from 130–700 °C under anoxic conditions and atmospheric pressure, during a maximum of 2 h. Changes in weight and the relative percentages of C, N, H and O are noted alongside modifications of the internal and external morphology. Vitrinite reflectance provides an elegant tool to determine the heating temperature of the residues. The kinetics that determine the changes and modifications are discussed. The resulting solid products of the heating process can be conveniently considered in five phases, which fit the physical and chemical properties. The simulation provides a rigorous basis for the study of the formation processes, as applied in the archaeology, after the so-called “carbonization” process.