The expansion of volume (the puffing index) of naked barley was investigated at various operating conditions of the puffing process. The purpose was to optimise the manufacture of expanded grains of the naked barley cultivars that have exceptional nutritional value for humans. The influence of the following parameters on the puffing index was investigated: the mass and the moisture content of the charge of the puffing barrel, pressure and temperature during the puffing process, the cultivar of barley, pre-processing of the grain (grinding and polishing), adding water into the barrel and the sensory quality of the product. A regression equation was established for the calculation of the puffing index as a function of the operating parameters. The puffing index is influenced especially by the operating temperature and pressure. There was no influence found of mass of the charge, the cultivar of barley, the degree of grinding of barley, washing of the grains and adding water on the puffing index. The puffing index is not the sole indicator of the quality of the expanded product. It is necessary to take into account the sensory evaluation. A quality expanded naked barley was obtained at the operating temperature of 550 degrees C and pressure from 0.9 to 1.0 MPa with the moisture content of the charge around 16.5%. (c) 2006 Elsevier Ltd. All rights reserved.