The ice layer around a prawn is glaze, and in the pack it is water weighed together with the product. The Codex Alimentarius standard for quick frozen shrimps or prawns (CXS 92-1981) requires net contents of glazed product to be declared without the glaze: if the pack says 1 kilo, the ice-free shrimp should weigh 1 kilo.
The standard's weighing method (section 7.3.2):
- Open the pack as soon as it leaves cold storage; put raw product in a container fed from the bottom with fresh water at room temperature at about 25 litres a minute, and let all the ice melt.
- Weigh a dry sieve with 2.8 mm apertures.
- When all glaze that can be seen or felt has gone and the shrimp separate easily, tip them onto the sieve and drain for 2 minutes at an angle of about 20 degrees.
- Weigh the loaded sieve and subtract the sieve; the result is the net content.
If the contract does not fix the glaze definition and this method, the point is argued again with every consignment: in a gross 1 kilo pack with glaze at 20 % of gross weight the product is 800 grams, and if the percentage is quoted on net weight the result changes.
The label carries two conditions as well (section 6): glazing with sea-water is stated, and the storage instruction reads minus 18 °C or colder.