A method for detecting a liquid composition applied onto a cellulose blank structure, with a detection system. The detection system forms part of a cellulose product forming unit for forming cellulose products from the cellulose blank structure. The detection system includes a detection unit connected to a control unit. The method includes: providing the cellulose blank structure and feeding the cellulose blank structure in a feeding direction, where the cellulose blank structure moves through an application area and a detection area, the application area being arranged upstream the detection area; applying the liquid composition onto the cellulose blank structure in the application area; detecting the applied liquid composition in the detection area with the detection unit; analysing a detection result formed by the detection by the control unit, thereby forming an analysis result; and initiating a control action by the control unit upon detection of an analysis result deviating from a pre-determined analysis result.