Determining the correct time when the harvest begins is a fundamental point in relation to a product that should have the necessary indicators of organoleptic and commercial properties. During the ripening of the fruit, changes and physical and chemical indicators which are expressed in the increase in the size of the fruit, reducing the density of pulp and decomposing starch with the formation of simple sugars are checked. Clarification of these phenomena with the practical tests, allows determine the correct timing of harvest.


The resistance of the pulp to compression tends to decrease with the approach of physiological ripening of the fruit. Each variety has its own specific indicators of density and the optimal moment of harvesting corresponds to them. The indicator is measured in kg/cm2 and determined by a tool called a penetrometer. A penetrometer is like a plunger tip capable of measuring the resistance of the pulp to compression, after removing from the fruit a small amount of peel, about 3 cm2. An apple plunger tip has a smooth round surface with a diameter of 11 mm. The selection of samples for test is fundamental; it is recommended to measure the resistance of fruit pulp picked from 10 different apple trees, at the height of human growth on the edge of the crown. Every single fruit is tested on both sides. The orientation table with the indexes of hardness for some varieties is below. Remember: the indexes should be combined with the Test of the starch.


The test gives a very reliable pattern of the direct starch content in apples and the maturity of apples. The gradual disappearing of starch can be visualized using the visual colorimetric method because starch in combination with Lugol’s solution (iodine solution in the water solution of potassium iodide) gives different coloring in accordance with the amount of starch in fruit at the time of testing. The solution is prepared by diluting 10g of potassium iodide plus 3g of crystallized iodine in 1 liter of water. The solution under the contact with the pulp of fruit that was cut in an appropriate manner shows different coloration of blue shades; the comparison of the blue shades with the proper/conformant photographic tables allows to determine the maturity of fruit. The fruit has to be cut according to primary great circle halfway point and dipped in the solution for almost one minute, during the time the sample gets a bluish coloration spreading over the surface of more or less full shade. The coloration should be compare to a photographic table. To make the analysis, it is necessary to select fruit samples for the test in accordance with the requirements listed for the penetrometer test

Varieties Starch test Hardeness (kg/sm2) RSR (°brix) Acidity (meq/100ml)
Braeburn 2,5 +/-0,2 8,2 12 9,4
Fuji 3,5 +/-0,2 index does not fit 14-15 6
Fiorina 3,5 +/-0,2 7 12,5-13 8
Gala (gruppo) 3,5 +/-0,2 7 +/-0,5 12-14 5
Golden and similar varieties 3+/-0,2 splitting is often irregular 6,5 +/-0,5 12 6-7
Gold Pink 3,5 +/-0,2 7,0 +/-0,5 14-16 8
Granny Smith 2,5 +/-0,2 7,5 +/-0,5 10-12 8-8,5
Imperatore and similar varieties 2,8 +/-0,2 7,0 +/-0,5 12,5-13 8-8,5
Primiera 3,5 +/-0,2 index does not fit 13,5 7
Red chief, Superchief, Red Cap 3,5 +/-0,2 7,0 +/-0,5 13-14 5
Red Delicious 2,34-0,2 6,5 +/-0,5 11-13 4-4,5
Renetta 2,5 +/-0,2 9+/-0,5 14 12
Stayman (group) 2,5 +/-0,2 7,0 +/-0,5 11-12 7,5-10

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