During the production of consumable liquids such as milk, soup, and juice, the liquid consumable may be transferred from one location to another location through a fluid conduit. For example, a consumable liquid may be transferred from a storage tank to another destination through piping. At the end of the process, the piping may be purged with a flushing fluid to push the liquid consumable remaining in the piping to the end destination, thus preventing the volume of liquid remaining in the piping from being wasted. To control the flushing processing, fluid flowing through the piping may be fluorometrically analyzed to determine a concentration of product in the fluid. The flushing liquid can then be controlled based on the determined concentration. For example, the supply of flushing liquid may be terminated when the concentration of product falls below a threshold, indicating the flushing liquid is diluting the liquid consumable.