A clean-in-place process may begin with a pre-rinse step in which soil (e.g., contaminants, residual product) is flushed from industrial equipment prior to circulating a cleaning agent through the equipment. To determine when the equipment has been suitably flushed, pre-rinse fluid exiting the industrial equipment and containing soil may be fluorometrically analyzed. A concentration of the soil is determined from fluorescent emissions emitted by the soil itself. Based on this information, the pre-rinse flushing process can be controlled, for example, to minimize water usage, maximize pre-rinse cleaning, or based on any other suitable metric.