SOP: Determination of Drained Weight of Canned Fruits and Vegetables
GIFSQ — Global Institute for Food Safety & Quality
Principle
The drained weight is the weight of the solid product after the packing medium has been drained off under standard conditions of sieve and time; it is expressed as a percentage of the water capacity of the sealed container. A washed drained weight removes all adhering substances from the solids before draining.
Apparatus required
- Circular sieve, 8 meshes to the inch (0.097 inch openings), set in a frame with vertical metal sides higher than the level of the product on the sieve — 8 inches in diameter for A2½ (401 × 411) size cans and smaller, 12 inches in diameter for No. 10 size cans; for tomatoes, a similar sieve with 2 meshes to the inch (0.446 inch openings)
- Weighing balance
Procedure — Drained weight
Tip the contents of the can onto the circular sieve so the product spreads evenly over it, and tilt the sieve so the syrup or brine drains away freely
↓
Allow the product to drain for 5 min
↓
Weigh the sieve with the drained contents, and weigh the dry sieve; the drained weight is the difference between the two
↓
Turn halves of apricots, guavas, peaches and pears cups down on the screen before draining
Procedure — Codex drained weight (CAC/RM 36-1970, 37-1970 and 44/49-1972)
Drain the product on a sieve of the following particulars for the stated time:
| Method | Capacity of container | Sieve diameter | Mesh openings | Time of draining |
|---|---|---|---|---|
| Method I — canned fruits and vegetables | Less than 1.5 kg | 20 cm | 2.8 × 2.8 mm | 2 min |
| Method I — canned fruits and vegetables | 1.5 kg and more | 30 cm | 2.8 × 2.8 mm | 2 min |
| Method II — canned tomatoes | Less than 1.5 kg | (illegible in the available copy) | (illegible in the available copy) | 2 min |
| Method II — canned tomatoes | 1.5 kg and more | 30 cm | (illegible in the available copy) | 2 min |
| Washed drained weight | — | 20 cm | 0.3 × 0.3 mm | 5 min |
↓
From the weights found, determine the % w/w liquid content and the % w/w drained weight (solid content)
Note: the sieve diameter and mesh openings for Method II are illegible in the available copy (the print reads “egis 9,” and “12 Xerte” for containers under 1.5 kg, and “Th2 M2” for containers of 1.5 kg and more). The washed drained weight particulars are legible as given.
Procedure — Washed drained weight (CAC/RM 44-49-1972)
Wash the contents from the can on to the tared fine mesh sieve
↓
On the sieve, wash the contents under running cold water and then with hot water until free of adhering substances
↓
Spread the material on the sieve, drain for 5 min, and weigh
Procedure — Proportions of component fruits or vegetables
After determining the drained weight, separate by hand the pieces of the various component fruits or vegetables, weigh them, and calculate the proportions as percentages of the total drained weight
Procedure — Vegetable content in vegetables in sauce
To determine the vegetable content of vegetables in sauce, empty the contents on the sieve used for determining drained weight and wash free of sauce with water
↓
Note the weight of the sieve and the washed vegetable
↓
Subtract the weight of the dry sieve, and calculate the vegetable content as a percentage of the net weight of the contents of the can
Calculation
Drained weight = (weight of sieve and drained contents) − (weight of dry sieve)
% w/w drained weight = (drained weight / weight of distilled water at 20 °C which the sealed container will hold when completely filled) × 100
Results of drained weight to meet Codex specifications are expressed as % w/w calculated on the basis of the weight of distilled water at 20 °C which the sealed container will hold when completely filled, and not on the basis of net weight of contents.
Precautions
- Distribute the product evenly on the sieve so that drainage is uniform.
- Turn halves of apricots, guavas, peaches and pears cups down on the screen.
- For the washed drained weight, wash until the material is free of adhering substances before draining.
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.
FAO/WHO Codex Alimentarius Commission, CAC/RM 36-1970, 37-1970 and 44/49-1972 — cited in the book.