There are numerous studies on food loss on the demand side examining consumer behavior towards food choice and food waste generation at the household level. In this paper, we target food loss on the supply side, with a focus on the industrial food processing environment. More specifically, we map food loss in each processing stage, that is sustainable operations. Primary data were conducted through a survey (complemented with observations and documentary analysis) in 47 food processing companies in Belgium to identify hotspots and quantify food loss. The findings show that processing is by far the most important food loss hotspot. While transportation, changeover, interrupted production, human errors and product effects at this stage often lead to substantial or excessive losses, causes of food loss during packaging and before or after production have a smaller impact. At subsector level, however, there are substantial differences with respect to the most important causes. The originality of this research can be evaluated in three ways: one, identifying hotspots of food loss in the industrial processing environment; two, measuring the magnitude of losses across different product categories and causes and three, how sustainable operations plays a significant role in food loss prevention.