An experimental study of single particle combustion is performed in a high temperature particle reactor. The particle degradation is simultaneously monitored by high magnification direct imaging and by shadowgraph imaging techniques giving access to the full behaviour of the particle even when enveloped by a flame. This allows tracing the time-resolved evolution of the particle shadow during its degradation as a function of its burnout. The method provides access to the whole process timeline, especially the onset of the heterogeneous oxidation even during the flame phase. It is observed to occur earlier for larger particles containing lower volatile matter. The latter occupies around 40% of the initial particle shadow, which decreases with devolatilisation progress following a power trend. The char burns at the surface until the reaction front penetrates the particle leaving an ash matrix behind. Effects of particle size and volatile matter on the different steps of particle combustion are discussed. Moreover, biomass behaviour is compared to that of coal. The whole results give new insights in the combustion of single biomass particle and are available for the development and validation of dedicated solid fuel combustion models.