The work presents evaluation of the influence of individual parameters of thermal treatment (variable time; thermal treatment in the condition of increased pressure / in steam) on chosen quality parameters of different varieties of potatoes (Satina, Asterix and Saturna). The principal aim of the research was to evaluate the influence of thermal treatment on chosen parameters (force, deformation), resulting from the characteristics of potato starch. Requirements of thermal treatment were chosen in order to achieve a suitable quality of the analysed varieties of potatoes, characterised by various amount of starch. Properties of force and deformation of the analysed potatoes were investigated with a Materials Testing Machine INSTRON 4301 (the penetration test). Analysed data strongly suggest that of all analysed varieties Asterix is of the highest nutritional value and usefulness, which may be connected with the quantity of starch observed in this variety.