This paper describes the result of a process study undertaken to determine the performance of the break- and reduction-rolls and plansifters in a commercial flour mill. The parameters measured included the flow rates of selected streams, their ash and moisture contents, and their particle size distributions. The percentage errors in the overall, ash and moisture balances across the plansifters ranged from −17.8 to +1.2, −10.1 to +15.5, and −0.4 to −3.1, respectively. The cumulative size distributions of the first, second and third break-roll outlet streams were found to normalize with respect to roll gap setting using only a single fitting parameter. Similar results were obtained for the first, third and fifth reduction rolls. The procedure was also partially successful in normalizing previously published break-milling data. The measured separation in the six plansifters studied was compared with an ideal separation on the basis of size, assuming that there was no breakdown or aggregation of individual particles within the plansifter. The results suggested that there were significant deviations from ideality.