Production Practices and Quality Assessment of Food Crops. Vol. 1

3. PRINCIPLES AND DEVICES FOR THE DETACHMENT
The application of a well directed energy is necessary to effect detachment; the
procedure in which this energy is applied is the first and basic consideration in
the aim of mechanical detachment and removal, and depends on the commodity
in question. Severing the attachment forces requires that the ultimate fatigue,
tensile or shear strength thresholds must be exceeded (Srivastava et al., 1993)
(Table 2).
3.1. Low-height herbaceous structures
Such as vegetables, strawberries. . . . We differentiate between root and surface
crops.
3.1.1. Root crops
Fruit and Vegetables Harvesting Systems 263
Table 1. Comparative damage thresholds for selected fruits.
Drop Height onto Average mass (g) Observations
hard surface causing
visible bruise a (mm)
Apple 010 220 High turgidity, increased
damage susceptibility
Pear 020 175
Peach 025 150 More susceptible
in compression
Apricot 150 060
Tomato 200 075 Skin most important
Orange, lemon 400 200 Rough surface, increased
damage susceptibility
due to friction
Olive (table) 200 30
Small fruits
Rubus 050 10
Ribes 120 10
Strawberries 050 30
Two different principles are used for the harvesting of these crops: digging (potatoes,
carrots, . . .) and pulling (carrots, leeks, . . .) (Ortiz-Cañavate and Hernanz, 1989;
Gracia and Palau, 1995).
Digging consists of the uprooting and lifting of the crop together with considerable
amounts of soil, which has to be separated, by the thrust of a digging or
plowing share. Working parameters of this system are: