The digital HPE II-FFF fruit firmness tester was calibrated using a test plate; this allowed a constant force (12.5 N) to be applied through the anvil (apple ø 5 mm). Fruit was stabilized in a plastic holder (length: 12.2 cm, width: 8.3 cm, height: 5 cm) and rotated in order to take 3 measurements around their perimeter. Firmness was determined as the average force in Newtons (N).