BS 809:1985 pdf free download.British Standard Methods for Sampling of milk and milk products.
0 Introduction
Correct sampling is an operation that requires most careful attention. Emphasis cannot therefore be too strongly laid on the necessity of obtaining a properly representative sample.
The procedures described in BS 809 are recognized as good practice to be followed whenever practicable. However, it is impossible to lay down fixed rules to be followed in every case, and, however explicit, they cannot fully take the place of judgement, skill and experience. In particular, unforeseen circumstances mey render some modifications desirable.
The samples obtained by the methods described in BS 809 are “laboratory samples” as defined an ISO 78/2, Layouts for standards — Part 2: Standard for chemvcal ana’ysis.
1 Scope and field of application
BS 809 specifies methods of sampling milk and milk products for microbiological, chemical, physical and sensory analysis.
It is not applicable for the selection of a number of units from a consignment, nor does it apply to subsequent operations in the laboratory.
Samples for microbiological examinations shall be taken first, using aseptic techniques and sterilized equipment and containers (see 5.1.1).
The precise method of sampling and the mass or volume of product to be taken varies with the nature of the product and the purpose for which samples are required (see section two).
The sample container shall be closed immediately after sampling.
For products in small retail containers, the sample shall consist of the contents of one or more unopened containers.
If necessary provide means, for example a temperature control sample, for the temperature of samples to be checked on arrival at the laboratory.
7 Preservation and storage of samples
Preservatives shall normally not be added to samples intended for microbiological or sensory examination.
A suitable preservative may be added to some milk products, provided that:
a) an instruction to do so is issued by the testing laboratory;
b) the preservative is of a nature that does not interfere with subsequent analyses;
c) the nature and quantity of preservative are indicated on the label and in the sampling report.
Table 1 indicates whether preservatives may be added and gives the recommended storage temperatures before transport for samples of various milk products. The storage temperature shall.be attained as quickly as possible after sampling,
The storage time before transport shall be as short as possiblc (see clause 8). Storage temperatures other than those recommended in table 1 may be used if requested by the testing laboratory (for example higher temperatures may be requested for some cheeses which could be adversely affected by the temperatures given in table 1).
The time and temperature shall be considered in combination and not independently.
8 Dispatch of samples
Samples shall be dispatched to reach the testing laboratory as soon as possible after sampling (preferably within 24 h). Durinç transit, precautions shall be taken to prevent exposure to contaminating odours, to direct sunlight and to temperatures out side the ranges given in table 1 or outside the ranges requested by the testing laboratory.
9.2.2.2 Extractors
9.2.2.2.1 Sample extraction cylinder
A suitable sample extraction cylinder is shown in figure 4. It consists of two perfectly adjusted concentric tubes, one of which revolves inside the other, and which are operated by a control in the head of the cylinder which turns through 900. Along the length of the two concentric tubes, in opposing positions, are slots 50 mm long and 6 mm wide, with a separation of 20 mm.
When the inner tube is turned to one extreme, the slots in both tubes coincide in an open position which allows liquid to flow into the cylinder. When the head is turned through 90° to the other extreme, the slots do not coincide and the cylinder is closed. The top and bottom ends of the cylinder are fined with screw-caps for easy cleaning. The length is variable, depending on the depth of the containers in which the cylinder is to be used, but in general, approximately 1 m is sufficient
9.2.2.2.2 Chamber probe
A suitable chamber probe is shown in figure 5. It consists of a hafl-round tube closed by a strip or plate which slides along grooves in the upper surface of the tube. The inner chamber is divided into compartments which increase in size from the lower end of the probe. The total length may vary, according to the depth of the container in which it is to be used, but, in general, approximately 1 m is sufficient.
The probe is inserted into the container until it touches the bottom, with the chamber closed. With the probe in a vertical position, the dosing Strip is gradually raised until it reaches the surface level of the liquid. Immediately the strip is lowered and the probe removed. By placing it in a horizontal position and opening the chamber, it is easy to observe the samples taken at different depths, which are kept separate by the partitions dividing the total length of the chamber.
The chamber is emptied by gently tipping the open probe over the sample container.
With this probe, samples can be taken to a depth of 5 mm from the bottom of a container.
9.2.2.2.3 Probe or partial sample extractor
A suitable probe or partial sample extractor is shown in figure 6. ft comprises a well-sealed compartment allowing sampling of a particular section of the tank or vessel. It allows samples to be taken at 10 mm or less from the bottom of the product container. The valve shall be perfectly adjusted so that the extractor can be removed without loss of the contents.
The valve can be opened easily by hand, by means of a cord. The extractor should be suspended from a cable which marks the depth reached by the lower end of the probe. It should weigh at least 3 kg.
The extent of mixing shall be appropriate to the period of time over which the milk has been at rest. The efficiency of the method of mixing apphed in any particular circumstances shall be demonstrated as being adequate for the purposes of the analysis envisaged: the criterion of mixing efficiency is the repeatability of analytical results from samples taken either from different parts of the consignments, or from the outlet of the tank at intervals during discharge. A method of mixing shall be considered efficient if the difference in fat content between two samples, taken under these conditions, is less than 0,1 %.
Mixing of the contents of large vessels or storage, rail and road tanks can be performed
— by a mechanical agitator built into the tank and driven by an electric motor
— by a propeller or agitator driven by an electric motor and placed on the manhole with the agitator suspended in the milk
— in the case of rail or road tankers by recirculation of the milk through the transfer hose attached to the tanker unloading pumps and inserted through the manhole
— in the case of vertical tanks by clean compressed air.
NOTES
1 When clean compressed air is recommended, it is necessary to use filtered compressed air from which all contaminants (including od. water and dust) have been excluded. The possibility of microbiological contamination should not be forgotten.
2 Minimal air pressure and volume should be used to prevent the development of rancid flavour.
In a large vessel, with a bottom discharge outlet, there may be, at the discharge point, a small quantity of milk which is not representative of the whole contents even after mixing. Accordingly, samples should preferably be taken through a manhole. If samples are taken from the discharge outlet. discharge sufficient milk to ensure that the samples are representative of the whole.
9.33.3 Skimmed milk and whey
Use the method described for whole milk in 9.3.3.2.2, 9.3.3.2.5 and 9.3.3.2.6.
9.3.3.4 Buttermilk, fermented milk, flavoured milk
Use the method described for whole milk in 9.3.3.2.2, 9.3.3.2.5 and 9.3.3.2.6 and take a sample before fat or other solid matter has had time to separate.
9.3.3.5 Cream
When using the plunging method for mixing cream, use the plunger in such a manner that the whole of the cream at the bottom of the container is thoroughly agitated and mixed with the upper layer. To avoid foaming, whipping or churning of the cream, do not raise the disc of the plunger above the surface of the cream during plunging. The equipment described in 9.2.1 (see figures 1 and 2) may be used.
9.4 Preservation, storage and dispatch of samples