The invention relates to a container (1) comprising a structure (10) of characteristic geometrical shape and of predetermined volume and at least one bag (11) arranged inside said structure (10) and suitable for receiving a food-grade liquid. The geometry and material of the structure (10) provide an inertia of function for folding or unfolding the structure (10) in order to reduce storage space either before the container (1) is filled or after the container (1) has been completely drained and an inertia of stacking of the containers (1) in order to optimize storage and facilitate the transportation of the containers (1). The container (1) is suitable for use with an unloader fitted with a pumping system for draining fresh food-grade liquid from the container (1) into a cooking device and filling used food-grade liquid from the cooking device to the container (1 ).