SOP: Cut-out Examination of Canned Fruits and Vegetables — General Examination
GIFSQ — Global Institute for Food Safety & Quality
Principle
Cut-out examination is the systematic opening and inspection of a canned product: the external condition of the can is recorded, the internal vacuum or pressure is measured with a gauge, and the contents are inspected for appearance, fill and visible defects before any analytical test is carried out.
Apparatus required
- Can opener (a good one)
- Vacuum and pressure gauge (indicating both vacuum and pressure) with hollow pointed end and rubber gasket
Procedure — External examination and weighing
Look over each unopened can: dents or scratches on the body, any leakage around the seams, and the state of the ends
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Record the ends with these terms: “Flat” — both ends concave, held in by a sufficient vacuum; “Flipper” — the vacuum too low to hold the ends, so a sharp blow against a solid object near the top may pop one or both ends outward (take care not to dent the can in doing this); “Springer” — one end bulged and the other flat, so that pressing the bulged end makes the flat end spring outward; “Swell” — both ends bulged outward by internal pressure strong enough to deform them permanently
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Record the gross weight of each can as it stands
Procedure — Vacuum or pressure measurement
Drive the hollow pointed end of the gauge through the lid so that the rubber gasket seats gas-tight and no vacuum is lost
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Dampen the rubber before fitting the gauge, and pierce the lid near one edge; press gently so the headspace is not disturbed
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Take the reading from the dial needle; record vacuum in inches of mercury and pressure in lb
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Do not measure the pressure of swollen cans, and do not use a vacuum gauge on swollen cans
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Correct the reading for altitude and temperature. Vacuum drops about 1 inch for each 1,000 ft of elevation gained — a can moved from sea level to 3,000 ft loses roughly 3 inches of vacuum, while one brought down from 3,000 ft gains about 3 inches. Readings may be stated at sea level: a product showing 15 inches at 3,000 ft has a sea-level vacuum of 15 + 3 = 18 inches
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For every 10 °F rise in temperature the vacuum falls by about 1.2 inches; for every 10 °F fall it rises by about 1.2 inches
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With a low initial vacuum, rising temperature or altitude can put the can under positive pressure. About 2 psig is enough to dome a cylindrical can of roughly 1 kg capacity into a flipper or springer; other can sizes need more or less pressure, depending on the end shape and the expansion-ring design. Flippers and springers usually come from poor vacuum and headspace, and only rarely from microbial spoilage
Procedure — Opening and inspection of contents
Cut the can open with a sound can opener
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The moment the can is opened, look at the surface of the contents: underfilling or overfilling shows at once, and this is the best point to catch cloudiness in the syrup or brine or a poor-looking fruit or vegetable
Precautions
- Do not press the vacuum gauge too hard against the lid, or the headspace will be altered.
- Never measure the pressure of a swollen can or apply a vacuum gauge to one.
- Do not dent the can while testing for a flipper.
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.
Joint FAO/WHO Food Standards Programme, Codex Alimentarius Sampling Plans for Prepackaged Foods (1969) (AQL 6.5) — cited in the book.