Apparent density, true density, specific volume and internal porosity were investigated during deep fat frying of french fries. The effect of frying conditions (oil temperature, sample thickness and oil type) on the above properties was examined. A simple mathematical model was used to correlate the above properties with oil and moisture content. Five parameters with physical meaning were incorporated into the model: the enclosed water density rho(w), the enclosed oil density rho(L), the dry solids density rho(s), the dry solids bulk density rho(bo) and the volume shrinkage coefficient beta＇. Moisture and oil content during deep fat frying and consequently all the examined properties are affected by frying conditions. The results showed that the porosity of french fries increases with oil temperature increases and sample thickness and it is higher for products fried with hydrogenated oil. (C) 2000 Elsevier Science Ltd. All rights reserved.