The viscoelastic behaviour of french fries during deep fat frying was examined under uniaxial compression tests, as a function of the main process variables (oil temperatures, oil type) for various frying times. The stress-strain data of the compression test were modelled using a simple mathematical model, containing parameters such as the maximum stress (sigma (max)), the maximum strain (epsilon (max)), the elasticity parameter (E) and the viscoelastic exponent (p). The effect of oil content, oil temperature and oil type on the compression behaviour of fried potatoes was introduced through the corresponding effects upon the model parameters. The results showed that maximum stress and maximum strain increase during frying. Crispness of potato strips is higher for hydrogenated oil, while the use of refined oil decreases potato crispness. (C) 2001 Elsevier Science Ltd. All rights reserved.