Two varieties of apples and pears were tested in the laboratory to measure their response to a small energy impact applied by an impact tester. Samples of fruits of increasing ripeness were tested over several weeks. Non-destructive impacts and other destructive and non-destructive measurements of ripeness were applied to the fruits. The non-destructive impact test was used to sort fruits with different firmness. New software was developed to control the impact test, calculate the I I parameters, and sort the fruits. This software creates and subsequently uses a database to carry out the sorting. An on-line impact device for automatic detection of firmness was then designed and tested. (C) 2002 Elsevier Science Ltd. All rights reserved.