6.4 Quality control
In this section the general inspection procedures that are needed for packaging materials are described. Specific checks on the quality of individual packaging materials are described in detail in Chapter 3 following the description of each material. It should be noted that the analysis and quality control of the final product itself is not covered in this publication and the reader is recommended to read one of the many texts available for specific foods.
It should be noted that for very small-scale enterprises no formal quality control schemes or quality control staff are normally employed. The quality of both packaging and products is checked informally by the owner and/or the operators. This is satisfactory provided the people involved know what to check for but as the size of a business increases it is necessary to adopt more formal procedures. This publications is intended for small to medium-scale producers and it therefore includes basic quality control procedures for packaging materials. Larger-scale industries, particularly those that export foods may have to consider more sophisticated quality control systems than those described here and it is recommended that they employ a specialist to advise on their specific requirements.
6.4.1 Incoming packaging
Quality control should be seen as a method of saving money and not as an unnecessary expense. The time and effort put into quality control should therefore be related to the nature and importance of the likely fault that is being checked for. For example splinters of glass in a bottle or jar (Section 3.1.1) is a hazard that is very important to both customers and manufacturers because of the risk of injury. On the other hand if a design on a label (Chapter 4) is a few millimetres out of alignment this is not so important and not worth spending a lot of money to check for.
These differences in importance give rise to a general classification of faults (or defects) into the following categories:
- critical fault
Critical faults are those that may injure an operator in the plant or a customer, or alternatively they may be so serious that they may cause the food to become unsafe. The example of glass splinters above is one example of a critical fault and another is faulty can seam dimensions (Section 3.1.3), which could allow food poisoning micro-organisms to enter a can and contaminate the food.
Major faults are those that make a package unsuitable for use in the process or result in a serious loss of money for a business (for example through wasted product, legal action etc). For example if glass containers are not vertical (Section 3.1.1) they may break in a filling machine, if layers of plastic Film on a roll are stuck together (Section 3.2.2) it cannot be unwound and used or if foil has too many pinholes (Section 3.2.3) its barrier properties are affected and it will not protect the food as required.
Minor faults are the majority of faults that occur in packaging materials. For example a printing ink may be slightly the wrong color, the dimensions of a glass bottle or jar may vary a little or a plastic film may have marks or ink smudges which make it less attractive.
It should be noted however that each producer should carefully consider the market in which the package is to compete. An acceptable package with a few minor faults in one market may be totally unacceptable for a different market situation.
When quality control procedures are being set up or reviewed it is important to record the types of faults that have occurred in the past as well as those that could occur. The manager of the food plant then decides which of these faults is so important that they are critical to the success of the business or health of the operators and customers. It is possible that in some processes them are no critical faults, but if they are likely to occur (especially with glass containers) they must be included. Next the manager decides which faults will lose the business money if they occur. These major faults may result from a problem that the packaging supplier has or they may be connected with preparation of the packaging materials in the food plant.
These critical and major faults are the ones that a quality control scheme will be designed to check for. It is not ususally worthwhile checking for minor faults on a routine basis, unless they result in customer complaints.
6.4.2 Requirements for routine inspection of packaging materials
To monitor the quality of packaging materials successfully, each incoming batch should be examined. Routine inspection requires the following:
- trained staff,
The most important of these is properly trained staff and it is desirable that all staff involved in a process are trained to look out for faults in packaging materials as they are being used (as well as other faults in the product or process). In addition it is desirable to have one member of the production staff who routinely examines the packaging material as it is purchased for a set of likely faults that are important (critical or major) and who knows from experience are likely to occur. The operators who fill the packs with product should also be trained to look out for packaging faults. The training should make sure that the operators draw the manager's attention to the faults and do not simply let the faulty pack go out with the others. In some cases a bonus system in which operators are paid for identifying faulty products or packages can be beneficial provided safeguards are in place to prevent fraud.
It is not usually necessary to spend time and money examining every package that is bought (an exception to this is the examination of glass jars or bottles, particularly if they are to be re-used and may have been used by customers to store non-food materials such as kerosene. Here every container must be checked and this is often most conveniently done by the operators who wash the jars/bottles).
More often an established procedure is set up in which a sample of containers is checked for the expected critical or major faults. Deciding on the number of samples to check is not an easy decision. The number will depend on how many packages there are in a load and the number of faults that have been found previously (the reliability of the supplier) among other factors. There are published statistical tables that can be used to decide on the number of packages to inspect. They are based on different risks that a processor will accept faulty packages if not enough are inspected. However these are only useful if they are agreed with the packaging supplier so that any faulty packs can be returned and the money refunded. In practice small-scale processors in developing countries rarely have such an arrangement with a packaging supplier and the cost of any faulty packs is carried by the processor. The reason for checking the packages in these situations is therefore to prevent harm to customers and to removeseriously faulty packages before they are filled and so save the business money and protect its reputation.
Space should be set aside in the packaging store room or in the processing area to check routinely both the quality of the packaging materials and the weight of filled packs. This does not need to be elaborate, and a table, a checkweighing scale and a few simple items of equipment are usually adequate.
6.4.3 Checking filled packs
The main checks that should be done on packaged foods are as follows:
- net weight,
It is a legal requirement in most countries that a package has the weight of the food written on the label and that the net weight of food inside the pack is not less that this. To be sure that the correct amount of food is being filled it is necessary to check the weight of a sample of filled containers (except for very low production rates it is usually not possible nor worthwhile to check every container).
To do this a scale is needed which has a package plus a known weight on one side (Figure 6-3). In the case of glass the heaviest container from a batch should be used. Samples taken during the day's production are placed on the other side of the scale. All should be equal to, or greater than, the test weight. If an automatic filler is used in the process a record of the average weight of five samples can be kept which is then written on a chart (Figure 6-4). This shows the trends in fill weight over a period of time and lets the operators know when the machine needs to be adjusted If filling is done by hand it is still necessary to check the fill weights but the chart is less valuable. Instead operators who fill the containers should be told routinely of the results of the checks so that they can make the necessary adjustments to their filling.
The number of samples that should be taken to check fill weight depends in part on the amount of food that is produced and the method of filling (hand filled containers usually need more frequent checking). As a rough guide one in every twenty packages could be checked, but the proper number of samples will vary according to the production. The check does not damage the packages and if their weight is satisfactory, they can be returned for sale.
The method of checking fill-weights described above is known as the Minimum Weight system and it is intended to make sure that every package of food contains at least the net weight that is shown on the label. This is the simplest system for small scale producers to operate. In Europe another system has been introduced to take account of the highly mechanized, automatic filling and packaging that is used by most producers. This is known as the Average Weight system and relies on a statistical probability that a known proportion of packages will be above the weight written on the label. This system is unnecessarily complex for small-scale producers and is intended to operate when producers use automatic filling and checkweighing machines. However, if small-scale producers are intending to export foods to Europe they should be aware of this system and the implications for both labelling and import restrictions. It is recommended that further advice is obtained from local Export Development Boards or their equivalents.
This is described in detail in Chapter 4. For routine quality control it is often sufficient to check that the correct label has been placed on a container in the correct position when the fill weight is being checked. In addition the general appearance of the pack and product (including any food smeared on the outside) and the integrity of the seal can be checked at this time.
6.4.5 Batch coding
It is important to be able to identify when a batch of food was produced so that proper stock control can be achieved. In this way packaged foods are sold in the sequence that they are produced and there is no risk of packages being left in the store room until they spoil. At its simplest a batch code is a single number which is stamped onto the label of all packages that contain food from that batch. The number is then increased by one for each subsequent batch. A written record is kept by the processor to show which numbers correspond to the date of production. This can also be a useful double check on the shelf-life of the food when the batch code is taken together with the sell-by date (see also Chapter 4).
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