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SOP: Tough String Test for Beans

GIFSQ — Global Institute for Food Safety & Quality

Principle

Strings are removed from individual bean pods and hung so that each string supports a 250 g clamp assembly; a string that supports the weight for five seconds or longer is considered a tough string, and the pods containing them are weighed and expressed as a percentage of the test sample.

Apparatus required

  • Weighted clamp: battery clamp (with the teeth filed off or turned back), spring-operated clothes pin, or binder clip presenting a flat clamping surface, with a weight attached so that the entire assembly of weight and clamp weighs 250 g (a bag containing lead pellets is convenient as a weight)
  • Weighing balance

Procedure

Take a representative sample of at least 285 g from the drained product and record its weight

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Snap the individual bean units and put aside any that show signs of tough strings

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Strip the strings from the pods, keeping the pod material for the final weighing

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Clip the weighted assembly onto one end of a string; hold the other end between the fingers (a piece of cloth helps the grip) and raise it gently

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If the string carries the 250 g assembly for at least 5 seconds, the bean unit counts as containing tough string

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If the string snaps in under 5 seconds, test any broken pieces 13 mm or longer again, to see whether those portions are tough

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Weigh the bean units found to contain tough strings

Calculation

% w/w pods containing tough strings = (pods containing tough strings (g) / test sample (g)) × 100

The texture of canned French (green) and wax beans shall not be fibrous, and not more than 5% (w/w) of the units may possess tough string.

Precautions

  • Use a representative sample of not less than 285 g from the drained product.
  • Retest broken parts that are 13 mm or longer before concluding the string is not tough.

References

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

Association of Official Analytical Chemists, Official Methods of Analysis, 10th edn., 1965 — cited in the book.

FAO/WHO Codex Alimentarius Commission, CAC/RM 39-1970 — cited in the book.