Test Method for Drained Net Weight of Frozen Fish Products

As you will know Article 8 of Directive 79/112/EEC (as amended by Directive 89/395) on the approximation of the laws of the Member States relating to the labelling, presentation and advertising of foodstuffs, requires that solid foodstuffs presented in a liquid medium, including when frozen, should be marked with the drained net weight in addition to the net weight. In the case of frozen fish products such as prawns this means the weight net of ice glaze.

In addition Article 8 of the Price Marking Order 1999, which implemented Directive 98/6 on consumer protection in the indication of the prices of products offered to consumers, requires that, in the case of pre-packaged solid food presented in a liquid medium, the unit price shall refer to the net drained weight of the product.

The DTI is conscious that, although the Food Labelling Directive requirement has not been implemented into UK law because of problems in identifying a test method, packers may be asked to mark the drained net weight in advance of a legal obligation to do so in order to permit retailers to comply with the price marking requirements applicable from 18 March 2000.

As you may know an industry guideline has been developed in respect of the marking of drained net weight for canned and bottled foodstuffs packed in liquid media. The enforcement authorities (LACOTS and ITSA) have agreed that adherence to this Guideline could provide a due diligence defence for enforcement purposes. It is also envisaged that, when legislation is made in response to the Fair Measure consultation which will include a drained weight marking requirement, the method is expected to form the basis of the legal requirement.

The DTI has therefore asked the Laboratory of the Government Chemist to produce the attached draft method for testing net of ice glaze markings. The method is derived from the CODEX and the Swedish methods.

I should be grateful for views by 31 May 2000 on whether the draft method is likely to provide an acceptable basis for an industry guideline and identify any additions or amendments.

We should be very happy to meet with industry and the enforcement authorities to discuss the issue.

Sue Billing

Internet: sue.billing@cacp.dti.gov.uk

Draft Method for the Determination of Net Content of Frozen (Block) Covered by Glaze

Introduction

This draft method is based on the Codex Alimentarius Commission (20th session), Codex Standard for quick frozen prawns/shimps (92/1981), Ice-Glaze on quick frozen prawns (No: V13), British Frozen Food Federation - Determination of Ice-Glaze for IF cooked and peeled prawns, French de-glazing method and Norwegian Standard method.

1. Scope

The method is designed to determine the net contents of raw and cooked quick frozen fish (herring, mackerel and other brown fish), prawns/shrimps covered by glaze.

2. Principle

The pre-weighed glazed sample is immersed into a water bath (temp. 20° C -27° C) by hand till all glaze is removed. As soon as the surface becomes rough, but still frozen (as felt by hand or 2min), remove the sample from the water bath and dry by use of paper towel, before re-weighing the sample to calculate the net weight (Assumed to be loss of ice glaze).

By this procedure thaw drip losses or re-freezing of adhering moisture can be avoided.

3. Requirements

3.1 At present the net weight of the pre-packaged product is controlled by Part V of the Weights & Measures Act 1985. Producers need to heed what are referred to as the three packers' rules :

a) the average weight of a batch should not be less that the stated weight,

b) no more than 2.5% of the pre-packages may have a weight less than T1, and

c) no pre-package may weigh less than T2.

In this context 'T1' is one tolerable negative error (TNE) below the stated weight, and 'T2' is two TNE below this weight. The TNE for a pre-package is dependent on the stated weight as follows:-

Table 1 Present TNE limits on indications of nominal weights

Where the TNE is a percentage of the stated weight it shall be rounded up to the next 0.1g.

3.2 Any tolerance for the drained weight (net of glazing) for the frozen produce needs to take account of the tolerances permitted in packing the product as well as the reproducibility of the test method used to determine the drained weight. Generally a packer will have a packing process with a variability of less than half the applicable TNE, and it is assumed that the reported reproducibility of the test method (about 4%) represent the 95% confidence level. Combining these two variables (root sum of squares) would give a tolerance figure appropriate for enforcement purposed tolerance (TNE) for drained weight of frozen product are as follows:

Table 2 Proposed TNE Limits on indications of nominal drained weight

3.3 The proposed figures takes into account that for packs greater than 300g, the drained net weight test method has the dominant affect, and that the determination of fish content (as opposed to ice-glaze) will show an improvement on the reproducibility figure from the collaborative trial report (J. Assoc. Publ. Analysts, 1989, 27, 85-108).

4. Testing plan

4.1 20 pre-packages, taken at random from the batch, shall be checked

4.2 Estimate X, the average deglazed net weight of the individual pre-packages making up a batch. A batch of pre-package shall be considered acceptable for the purpose of this check, if the mean value(x = the sum of the actual deglazed weight of the sample of pre-packed divided by 20) is greater than or equal to:

A_n = the nominal deglazed net weight of the pre-package

s = the estimated standard deviation of the actual contents of the batch*

t = 0.995 confidence level of a Students distribution with 19 degrees of freedom

* the value of the estimated standard deviation is calculated using the following expression

Thus the criteria for acceptance or rejection of the average X of the batch of pre-packages are

4.3 Testing for the number of defectives in the batch shall be carried out using the deglazed weight of the 20 pre-packages taken at random for the average test.

4.4 If the number of defective units found in the sample is less than or equal to 1, then the batch shall be considered to be acceptable.

4.5 If the number of defective units found in the sample is equal to or greater than 2, then the batch shall be rejected.

4.6 If the batch fails to satisfy the requirements of the Testing Plan then the batch will require rectification. Where appropriate, batches may be blended together or sorted, in order for the requirement of the Guidelines to be met. If this is not appropriate, then the batch must be disposed as specified in Regulations 24 of the Weights & Measures (Packaged Goods) Regulations 1986.

5. Reagents

None

6. Apparatus

6.1. Analytical Balance -accurate to 0.1g.

6.2. Container to weigh samples (e.g. Plate)

6.3. Sieve - circular sieve with diameter of 20cm or 30 cm (depending on pack size or fillet) and mesh size 2.8mm (conforming to ISO R565).

6.4. Water Bath - capable of containing water (at 20-27°C) equal in weight to 8 - 10 times the samples taken.

6.5. Thermometer - To read (20-30 ± 2°C)

6.6. Paper Towel

7. Procedure

7.1. Place the sample in a freezer of temperature -20 ± 2° C and allow to equilibrate. Remove the sample from the freezer. After removal of packaging, place on to a dry container (plate) and accurately weigh to one decimal point (0.1g) (M₀). Transfer sample immediately to sieve.

7.2. Transfer the weighed portion on sieve into the water bath and keep immersed until all the glaze that can be seen or felt has been removed (i.e. when the external surface of the sample is rough).

Note: The time for the glaze to be removed, will vary from product to product and size of samples.

7.3. Remove the sieve with sample, incline the sieve at an angle of about 20° and drain for 2 minutes*/ remove the excess water by use of a paper towel (without pressure). Reweigh the sample on the dry container (M₁). Calculate the weight difference.

* small products will take less time e.g. about 30 seconds for shrimps.

8. Expression of Results

The ice glaze content of the original sample, expressed as a percentage by weight, is given by:

% ice glaze content = 100 x (M₀ - M₁)/M₁

where :

M₀ is the initial frozen weight taken (5.1)

M₁ is the observed deglazed weight (5.3)

The deglazed net weight of the package is Mi, this value is used for the average and defective test in para 4. Individual pre-packages having a deglazed net weight less than the stated (nominal) deglazed net weight by more than the TNE laid down in Table 2 will be defined as a defective.

9. Recommendations

9.1 The three packer's rules should apply to the deglazed net weight.

9.2 'Proposed TNE' shown in the table above should be the TNE applicable to the deglazed weight of ice-glazed products.

9.3 The 'e' mark can only be applied to the nominal weight (the weight including the ice glaze) at present, in compliance with the Directive 76/211/EEC.

9.4 The declaration of the drained weight should be clear, and not be confused with the net weight declaration on the product.

9.5 The manner of marking the drained weight should the be same as that specified for the net weight in the Directive - indelible, easily legible and visible on the prepackage in normal conditions of presentation - and with the same minimum height requirements.

9.6 There should be an industry standard specifying the maximum quantity of added glaze necessary to preserve and protect the product, in order to prevent the use of excessive glaze from giving a misleading impression of the quantity of product.

For information only: from the Swedish method

Size classification

The size classification Shelled prawns(Pandalus borsalis)

The size is measured as the number of prawns per 500g including frosting.

This can be added if necessary, by making an addition on the basis of :
standard frosting of 8-10% below 250g
standard frosting of 8-12% between 250g and 350g
standard frosting of 12-14% between 350g and 500g

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