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The cleaning and disinfection programme may be controlled by visual or bacteriological methods. If visual control is used it must be done in a systematic way and personnel must be especially trained. However, neither visual nor bacteriological control will individually give enough information on cleaning and disinfection efficiency but if used at the same time or at different times (staggered) it will be possible to evaluate the efficiency of the cleaning and disinfection programme.

8.1 Visual control of cleaning standard

The purpose of visual control is to note if the surfaces are clean. If they are insufficiently cleaned, then visual control will inform on:

  1. The type of contamination

  2. The seriousness of the contamination

  3. Whether dry or wet surfaces should be controlled

  1. The measures to be taken to remove the contamination may differ depending on the type of contamination (i.e. types of soil, see 4.1).

  2. It is important to know if the contamination has to be removed immediately to secure hygienic production, or if it will be sufficient to remove the contamination by planned periodical cleaning or a special cleaning procedure.

  3. Dry or wet surfaces are estimated in different ways concerning the degree of contamination. It is easier to find contamination (soil) on dry surfaces than on wet surfaces. Therefore it must be decided if the control will be carried out on dry or wet surfaces. Standards for dry and wet surfaces shall be laid down. Results from dry and wet surfaces must never be compared without adjustments.

When establishing a visual control procedure, the main task is to establish a common language of reference and to define an acceptable level of visual standard among the personnel whose work should be controlled. The acceptable level of visual standard may also vary between the different areas and different equipment in the slaughterhouse.

It is recommended that visual control is standardized, perhaps by filling out preprinted forms. If several persons from time to time do the visual control, they must have common training to avoid great differences in the evaluation level.

8.2 Other control measures

It may be convenient to control:

The working routines of the cleaning procedures should be controlled to assure that the planned routines are respected. Otherwise the routines may change into less optimal (less hygienic) routines.

Working clothes should be controlled to assure a certain hygienic level. Staff must be controlled that they do not use the working clothes outside the processing area.

Personal hygiene should be controlled, especially hand-washing. Good personal hygiene habits should be encouraged by correct and sufficient installations (hand-washing basins, toilets/latrines and bathrooms (showers).

Appropriate personal hygiene should be enforced. However, since hygiene is often considered as personal, it should be done tactfully.

A solution may be to impress on the staff the need for good hygiene habits perhaps by a few short lessons, e.g. when a person starts employment, and also via encouragement and enforcement of good hygiene habits (see Appendix 1).

8.3 Bacteriological control

A simple and relatively accurate method to check the number of microorganisms on equipment or surfaces is the agar sausage method.

The equipment which is necessary for this method consists of:

Sterile agar sausages, diameter 40 mm (media-types: plate-count and MacConkey agar in artificial casings)

Sterile Petri dishes (diameter 9 cm)

Sterile plastic bags

Sterile knives

Gas or spirit burner


The agar sausage method can be used for all sorts of equipment, e.g. conveyors, tables, hooks, knives etc.

Technique: The cut surface of the agar sausage is pressed lightly against the surface of the equipment which has to be checked. In this way a stamp of the bacteria on the surface of the equipment is transferred to the sterile surface of the agar sausage. The stamped surface is sliced off (0.5 cm thick slice) with the sterile knife and transferred to the sterile Petri dish (the exposed surface upwards). The knife should be sterilized before a new sample is taken. Three slices (stamps) are taken from each piece of equipment. A normal size Petri dish can take 3 slices. The Petri dishes should be properly marked with code nos., dates, etc. before they are placed in the sterile plastic bags (to avoid dryness) and incubated at room temperature for 2 days.

Interpretation of results: after 2 days' incubation the number of bacterial colonies are counted. The number indicates the bacteriological cleanliness of the checked equipment and gives a good impression of the efficiency of cleaning and disinfection.

The following can be taken as a guide:

xxx = more than 100 colonies on 3 slices

xx = more than 100 colonies on 2 slices

x = more than 100 colonies on 1 slice

- = less than 100 colonies on 3 slices

As a guideline none of the 3 agar slices should develop more than 100 colonies if cleaning and disinfection of equipment has been efficient

Fig. 13 shows the principle when using the agar sausage method for bacteriological control.

Fig. 13. The agar sausage method

Fig. 13.

This guideline depends on the type of production. The limit of 100 colonies may be too low if the control is taken on surfaces in the dirty area of a slaughterhouse but the limit of 100 colonies may be too high if the control is carried out on knives used for heat-treated meat.

The management of a slaughterhouse/slaughter facilities will have to plan bacteriological control by deciding:

The agar sausage technique has been further developed resulting in:

These methods are based on the same principle as the agar sausage technique but the surface area differs. To compare results from different methods it may be convenient to calculate the number of colonies per cm2. It may be practical just to use one method and then lay down the acceptable number of colonies for different areas.

Other techniques may be used, but further facilities concerning laboratories and qualified staff will be required.

8.4 Conclusion

Both bacteriological and visual control will give the management of a slaughterhouse much information on the hygienic standard. If both methods are used and the results are evaluated together, it will probably reveal more quickly the points where hygiene must be improved. In other words, the results from bacteriological control will reveal requirements for disinfection and those from visual control requirements for an improved cleaning process.

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