Different physical parameters related to firmness were studied for apple fruit. Fruit were kept in different conditions up to 30 weeks to show a wide range of mechanical behaviour. Refrigerated storage, regular storage frequently applied in small farm in Poland, and storage with artificial high temperature were used in this study to ensure different softness of fruit. Water potential of apple flesh was measured using the HR-33T microvoltmeter equipped with the C-52 sample chamber. The most important mechanical factors related to fruit firmness were determined in different way using Instron machine equipped in each case with special adapters. Application of simple devices designed by the authors for the estimation of the slight changes in fruit firmness during storage is presented.