Energy expenditure during grain grinding using reciprocal quern and rotary quern

Previous experimental archaeology studies have shown that the transition from reciprocal quern to rotary quern in the Iron Age saved grinding women 75 % of the time and muscle activation per amount of ground grain. However, whether the detected between-quern differences in time and overall muscle activation reflect differences in energy cost is unclear. Here, we used indirect calorimetry (analysis of oxygen consumption and carbon dioxide production) to measure the energy expenditure during grinding on a Neolithic reciprocal quern and an Iron Age bun-shaped rotary quern in adult females (n = 30). Our results revealed that rotary quern grinding required a 123–153 % higher energy expenditure per minute (by about 2.7 kcal per minute of grinding) but a 42–49 % lower net cost of grinding, i.e., energy expenditure per given amount of grain (by about 74 kcal per kilogram of grain) compared to reciprocal quern. We estimated that transitioning from reciprocal to rotary quern reduced women's daily subsistence costs by 100–300 kcal.