SOP: Determination of Fruit Firmness Using a Hand Pressure Tester
GIFSQ — Global Institute for Food Safety & Quality
Principle
The Magness-Taylor pressure tester measures the maximum force required to push a cylindrical metal probe into the flesh of a fruit to a given depth; the force recorded indicates the firmness of the fruit and is used to determine softening during maturity and ripening. The larger (7/16 inch) punch is used on softer materials and the smaller (5/16 inch) punch on firmer materials; the choice of the 10 lb or 30 lb spring scale depends on the firmness of the test material. The fruit is usually peeled to overcome the interference of the skin with the action of the plunger.
Apparatus required
- Hand-operated pressure tester (Magness-Taylor type), with 10 lb or 30 lb force spring and one or two punches (5/16 or 7/16 inch in diameter), the punch marked with the required depth of penetration
Sample preparation
Peel the fruit so that the skin does not interfere with the plunger.
Procedure
Select the punch (5/16 inch for firmer materials, 7/16 inch for softer materials) and the force spring (10 lb or 30 lb) according to the firmness of the test material
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Press the plunger tip against the surface of the peeled fruit
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Force the plunger into the fruit with steady pressure until the marked line on the pressure tip reaches the required depth of penetration
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Read the force recorded on the pressure tester; this is the pressure-test reading of the fruit in pounds
Calculation
The pressure-test reading indicates the firmness of the fruit. For varieties of apples, the degree of ripeness is read from the following table:
- Delicious: Hard 17–20, Firm 14–17, Firm-ripe 11–14, Ripe 8–11
- Rome Beauty: Hard 18–23, Firm 15–18, Firm-ripe 12–15, Ripe 10–12
Where,
- All readings are in pounds (pressure-test reading in pounds).
Precautions
- Apply steady, even pressure.
- Peel the fruit before testing.
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.