Straw is used as fuel in grate boilers in Denmark to produce heat and electricity. One of the technical problems in these biomass boilers is the formation of an alkali-rich ash deposit, which may seriously affect heat transfer to the plant steam cycle and cause degradation of steam tubes by corrosion. While the processes of boiler ash deposit formation for both coal and biomass have been the scope of many studies, knowledge on the shedding process is limited. A newly developed cooled deposit probe was applied in order to perform shedding measurements in the boiler chamber of the straw-fired Avedore grate boiler, Unit AVV2, where both qualitative measurements, i.e., video recording, and quantitative measurements, i.e., probe heat uptake and probe deposit mass gain, were performed. The probe was placed in the top of the furnace, close to the superheater. The experimental study showed that in the case of the straw-fired Avedore Power Station the flue gas temperature around the secondary superheaters is so high (900-1100 degrees C) and the deposit has such a low melting temperature that the main shedding mechanism is the removal of molten ash deposits due to gravity. It was observed that the flue gas temperature influences the fraction of melt in the deposit and thereby to a high degree controls the ash deposit removal rate. The newly developed deposit probe proved to be a useful tool for the investigation of shedding of ash deposit.