Smaller fragment size facilitates energy-efficient bone grease production

Abstract

Conventional zooarchaeological wisdom holds that reduction of bone into small fragments, modally 2–5 cm in maximum dimension, facilitates the extraction of bone grease. However, experiments by Church and Lyman showed no statistically significant differences in amounts of grease extracted from 1 cm, 2 cm, and 4 cm bone fragments. Our research assessed whether other factors, including water and fuel inputs, could influence the degree of bone comminution for grease extraction. Experimental grease extraction from 15 cattle (Bos taurus) femora, reduced to similar maximum dimensions as in the Church and Lyman study, supports their finding that grease yield does not significantly increase in fragments <4 cm. However, our research shows that smaller fragment sizes require less water, and hence less fuel, to produce the same grease yields. These results suggest a tradeoff between the work it takes to produce very small modal bone fragment size and broader-scale fuel, water, and human energy budgets.