A system to produce a bitumen-based membrane provided with a bituminous surface covered by grains. The system comprises a movement device designed to more a preformed membrane in a predefined feed direction, a grain application machine comprising a rotating application drum provided with a plurality of cavities which are designed to receive grains in a loading region of said drum, a grain loading device designed to load the grains in the cavities in the loading region of the drum, and a grain retention device made of sintered polymer material, which is arranged in contact with a retention region for retaining the outer surface of the application drum so as to maintain the grains in the cavities until the latter reach an angular discharge position.