True Baroque organ music can only come back to life in the 21st century by developing Cu-based alloys and implementing them in the organ reed pipes. Reed pipes contain a vibrating part, the brass tongue that crucially influences its sound. Energy dispersive synchrotron X-ray diffraction has been performed in order to investigate residual stresses in the tongues. The in depth analysis gives us an important indication on the processes the tongues were submitted to during their manufacturing: hammering, annealing, filing to the neat thickness, curving of the tongues. A biaxial stress state in the organ tongues was considered. The residual stress values and behaviour were correlated to the manufacturing processes.