SOP: Determination of Maturity of French Beans by Shear Test

GIFSQ — Global Institute for Food Safety & Quality

Principle

As French (green) beans mature they become fibrous and the force required to shear them increases. Using a single shear blade (similar to the Warner-Bratzler shear blade), the force required to shear beans placed edgewise and flat is measured; in tender beans the edgewise force is generally more than the flat-position force, and the trend is reversed in mature beans. A single force threshold marks the over-mature point.

Apparatus required

• Shear texturometer with a single shear blade (Warner-Bratzler type, as designed by Voisey and Hansen)

Procedure

Place the beans edgewise in the instrument and shear with the single blade; record the force required

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Place beans in the flat position and shear; record the force required

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Compare the edgewise and flat-position forces

Calculation

• A value of 9 kg force and above indicates over-mature beans.
• Below 9 kg force, the beans are tender.
• In tender beans the edgewise shearing force is generally more than the flat-position force; in mature beans the trend is reversed.

Precautions

• Test beans of the same variety and growing conditions for comparable results.

References

Voisey, P.W. & Hansen, H., Food Technology, 21, 355 (1967).

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.