A system for continuous determination of mass transfers during brining operations is described and experimentally checked with herring. The system is based on the measurement of the apparent mass of a food product batch immersed in a brine and verifies several hypotheses concerning their behaviour during brining. The accuracy of these hypotheses was checked experimentally with respect to herring fillets immersed in saturated binary solutions (water + salt), and the simulation derived from the system was assessed. The simulated mass transfers were found to be quite precise, and the system also enabled assessment of the magnitude of initial water and fat contents in processed batches of herrings.