Water and steam blanching were investigated as pretreatments of bitter orange peels in order to modulate their bitterness before further formulation processing such as osmotic treatment and drying. The fruit pieces were water blanched at 95 °C for 10 min and at 85 °C for 60 min and steam blanched at atmospheric pressure during 5 min. The kinetics of water inflow and bitter flavanone losses were established from the variation of moisture and bitter com- pound contents during the blanching process. The whiteness and the citrus color indexes were adopted to evaluate respectively the color of the flavedo and the albedo. Thin sections of fresh and treated peels were resin embedded for light micros- copy evaluation and optical porosity determination. Results revealed that water blanching could partially debitter the peels by removing about 38 and 48 % of bitter flavanones (naringin, neohesperidin, neoeriocitrin) respectively at 95 and 85 °C. The citrus color index and the whiteness index decreased during the process denoting a flavedo discoloring and an albedo darkening. By contrast, the steam blanching showed good retention of bitter compounds. The color of the flavedo was unaffected by steaming while the whiteness index decreased. At microscopic level, the water-blanched peels exhibited an extreme swelling of the cell walls and slight disintegration of the tissue. Contrariwise, the steam blanching maintained the structure of the peels and brought about the shrinkage of the albedo tissue and the decrease of porosity.