Determining the temperatures to which the bone was heated in archaeological contexts. Distinguishing between boiled and grilled bones

Abstract

A study carried out in fresh cow (Bos taurus) cortical-femur bones which allows determining the maximum annealing temperature to which a bone was subjected is shown. It is focused on temperatures near the ones used in culinary activities. Mechanical spectroscopy, optical microscopy, differential thermal analysis and thermogravimetry studies are used in the present work. The study takes into account the behaviour of the thermal denaturation processes from the remnant collagen as a function of temperature. The survey of the relaxation process related to the triple helix to random coil transition from the residual collagen which occurs at 510 K/ 237 ◦C, is proposed as a potentially useful tool for determining that the bone was not previously heated above this temperature. In addition, by using mechanical spectroscopy a procedure for discriminating between grilledand boiled-bones is shown. Likewise, a reference chart of the thermodynamic states of denaturation of collagen in the bone as a function both of temperature and cooking mode is reported. The relationships between the denaturation stages and the responses from mechanical spectroscopy and differential thermal analysis are also shown.