The present invention relates to a system (70) comprising at least one coffee machine (10) and at least one accessory device (30) associated with said coffee machine, as well as to a method for controlling operation of such system, which allow to adjust the characteristics of the panel of coffee powder that are required for preparing a coffee-based beverage in order to obtain a high quality beverage. The invention provides for storing in a memory, for each coffee-based beverage that can be prepared by the coffee machine, a reference profile of the water flow rate flowing through the panel of coffee powder as a function of time, detecting the actual profile of said flow rate, and comparing the actual profile of the flow rate with the reference profile in order to ascertain deviations that are higher than a predetermined threshold. If deviations that are higher said threshold are ascertained, the invention provides for identifying and implementing suitable corrective actions before the subsequent brewing of a same beverage.