To sanitize a water distribution system, the system may be flushed with a proprietary sanitizing agent, or with copious fresh, clean water (dilution being ‘the solution to pollution’). Water entering the system may be subjected to ultra-violet light treatment, or be chlorinated to reduce its microbial load. Chlorine is often added to public water supplies at 0.1–0.2 ppm, as free chlorine ions are an active biocide. Further chlorination of water at the food premises may raise the chlorine concentration to 0.5 ppm or above; however, in some countries, e.g. in the EU, hyperchlorination of water (to levels greater than 0.5 ppm) has been outlawed. When water has been chlorinated, it is advisable to test the chlorine level on a regular basis to ensure it remains within the desired limits. Proprietary test kits are available for such monitoring procedures.
and safe use of the equipment, and the equipment is suitable for the job.
For example, brushes with long handles may be required to reach the high- level areas, or different-coloured equipment may be used in different parts of the premises to prevent cross-contamination. The provision of services such as hot water, drainage or electricity must also be taken into account when selecting the method and equipment for cleaning procedures. Most importantly, the nature of the premises and equipment to be cleaned must be considered, both to ensure effective cleaning and to prevent damage being caused by the cleaning operation itself.
Instructions to personnel should be clear and simple, and laid down as a formal procedure that is monitored on a regular basis. These instructions often take the form of a ‘Cleaning Schedule’, against which the performance of the cleaning team is audited. It is the premises manager’s responsibility to ensure that a cleaning schedule is prepared, is communicated to the cleaning team, and is reviewed in response to cleaning failures or alterations in the premises or production, and at regular intervals. The manager should be aware that it is not sufficient merely to give a copy of the cleaning schedule to the cleaning team and to expect its contents to be adhered to, but that each member of the team should be trained and updated with any changes to the cleaning schedule. Literacy problems, time constraints, paper overload and apathy all contribute to personnel not reading and understanding written instructions, so care should be taken to demonstrate procedures and discuss the process. Often, when personnel understand the reason why a particular procedure is required, that procedure will be carried out with far more dedication than if the procedure seems pointless. A major part of the manager’s role in personnel management is staff motivation, and this can only be achieved if the manager shows commitment to high standards.
The manager must also be aware of the sources of the costs of cleaning. As a rough guide, labour, or personnel costs, will comprise up to 70% of the overall cost of cleaning, equipment and chemicals a further 20%, and services (water, drainage, electricity) the remainder.
The Cleaning Schedule
The Cleaning Schedule should be a user-friendly document, containing detailed instructions for the sanitation of the premises. It should include safety information on all procedures and chemicals used, and should also detail a system for the monitoring and control of the sanitation procedure.
The Schedule should detail what is to be cleaned, by whom, when and how it should be cleaned. When drawing up a Cleaning Schedule, the manager needs to take into account the construction and layout of the plant, and the time required to clean a particular area or piece of equipment. The cleaning process should progress in a logical manner, so that there is no risk of re-contamination of previously cleaned items. For example, if the floor was cleaned before the walls, then the dirty water and residue from the walls would flow onto the floor, making it dirty once more. The
manager should also take into account the existing cleaning routines in use in the premises, as these have often developed over time into a form that makes the task easier or quicker for the cleaning team. Good points in the existing routine may be retained, but care must be taken to ensure that the cleaning procedure is effective. The Cleaning Schedule should detail all the chemical agents to be used during the cleaning process, and their correct use, including safety information, dilution instructions and method of application. It is important also to include a prescribed system of audit and review, detailing the persons responsible for each task, and exactly how often the area or item should be cleaned, inspected or sampled. To audit the cleaning process, regular visual inspections should be carried out, supplemented by microbiological sampling of equipment, particularly of food contact equipment. It is also important, however, to sample items that are not in contact with foods, as the entire premises should be cleaned to an equal standard. As a guideline level, Total Viable Count on cleaned surfaces prior to production beginning should be no more than 100 cfu/cm2, and there should be no evidence of faecal contamination, which may be demonstrated by analysing the sample for Enterobacteriaceae.
The sanitation process
Cleaning involves systematic application of energy to a surface in order to remove soil. This energy can consist of thermal energy – such as the use of hot water or steam, chemical energy – from detergents and disinfectants, and kinetic energy – the product of manual labour, mechanical cleaning tools or water turbulence within pipes and containers. A cleaning process will normally begin with a pre-clean phase, where visible debris is removed manually, perhaps using a brush or squeegee. Next is the cleaning phase proper. Manual cleaning, using hand-held tools, is often used for smaller pieces of equipment, which may have to be dismantled prior to cleaning.
Neutral or near-neutral detergents are used due to the close proximity of the operator, for safety reasons. Detergents with greater acidity or alkalinity are used in cleaning operations set a little more remote from the worker. These compounds, which may form a foam or gel, are sprayed onto large areas of the premises using special apparatus, such as a pressure lance, and are ideal for cleaning areas where access is restricted. The foaming nature of such detergents improve contact between the detergent and the surface, whilst gel detergents adhere even more closely to the surface, giving a prolonged contact time during which the chemical cleaning process takes place. The detergent may be mixed with hot water in order to benefit from thermal energy effects as well.
After the cleaning phase, which would include sufficient contact time for any chemical agents used to be fully effective, the equipment and surfaces are rinsed with potable water. A disinfection phase may then begin, where a sanitizer is applied to the surfaces and equipment. After the required contact time, the sanitizer may then be rinsed off with potable
water. Some food-safe chemicals, however, are designed to remain on the surface and do not require rinsing.
Water turbulence as a form of kinetic energy cleaning is commonly used in the dairy industry, and is often combined with thermal energy (very hot water) and chemical compounds. The cleaning effected here is carried out by a Clean-In-Place (CIP) system, where the cleaning solution is automatically circulated at high velocity through the pipes and containers of the production line. Highly acidic or highly alkaline detergents may be used, as the system is closed, allowing no access by personnel, and the flow rate of the solution is critical to ensure that there is sufficient turbulence in the system to effect cleaning (Fig. 3.7). Here, as in water distribution systems, blind-ended junctions on pipes can be bypassed by the cleaning solution, and contaminated food residue may remain. As a general rule, if there is a blind branch on the pipe, its height should be no more than three times the diameter of the main pipe, and where blind branches occur on bends, the cleaning solution should be directed into the branch at high velocity to ensure adequate cleaning.
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(b)
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Fig. 3.7. Water flow effects of internal cleaning of pipes. (a) Where flow is directed at a branch, turbulence is high and cleaning is good; (b) where flow curves past a branch, turbulence in the branch is low and cleaning is poor; and (c) where flow passes a
perpendicular branch, turbulence is very low and cleaning very poor. If the branch is three times longer than the diameter of the pipe, air will be trapped in the blind end, and the cleaning fluid will not even contact the surfaces.
Detergents
There are a number of different classes of detergent, with differing properties. Desireable characteristics of detergents to be used in food premises include being non-tainting, non-toxic and non-corrosive. They should be effective when used at low temperatures and at low concentrations, for operator safety, and should easily be rinsed off when the cleaning process is completed. It should be a simple measure to detect residues of the chemical to prevent tainting of the food, and the run-off waste effluent should be biodegradable and not harmful to the environment. The product used, however, should be sufficiently stable that its efficacy remains for a sufficient period of time to ensure sanitation before the compound degrades, and the product should be cost-effective for use in business.
Detergents are often described in terms of their surfactancy (ability to reduce the surface tension of the solution to improve wetting of the surface to be cleaned), dispersion (ability to break up particles of dirt or grease) and suspension (ability to keep the particles afloat within the rinse water so that they are removed from the surface). In general, a detergent molecule has a hydrophilic end and a hydrophobic end. When the detergent solution contacts oil- or fat-based residues on a surface, the hydrophobic portion buries itself in the residue, leaving the hydrophilic tail within the water of the detergent solution. As the detergent molecules squeeze into the residue, the residue is divided up into globules, the surfaces of which are covered in the hydrophilic tails of the detergent molecules (Fig. 3.8).
These globules of residue are then lifted off the surface being cleaned, into suspension and can be rinsed off.
Commonly used chemicals in the food industry include halogen-based compounds, quaternary ammonium compounds, amphoteric compounds and acids or alkalis.
Halogen-based compounds
Halogen-based compounds release free chlorine radicals as the active agent, which react with the cell wall constituents of food residues and microorganisms. They are non-tainting, biodegrade into non-toxic compounds, and can be detected using a simple chemical test kit. However, the solution has limited stability, and is quickly inactivated in the presence of organic material, e.g. food residues. Some halogen-based compounds release iodine rather than chlorine, but these are more corrosive, and are more likely to cause tainting of foods.
Quarternary ammonium compounds
Quaternary ammonium compounds are effective at neutral pH, so are suitable for use with manual cleaning procedures. They act by damaging the cytoplasmic membrane of cells in the residue. They are non-toxic, can
be detected using a chemical test kit, and most are biodegradable.
However, they may cause tainting of foods, and are inactivated in the presence of organic material, and also by excessive lime in hard water.
Amphoteric compounds
Amphoteric compounds contain long-chain substituted amino acids, and are unaffected by the mineral content of the water used. They are non- tainting, stable but biodegradable, and have low toxicity. They can be detected chemically, and are compatible with other classes of detergent and sanitizer, but they require a long contact time to complete their function.
Acids and alkalis
Acids and alkalis have long been used in cleaning products, and they act by oxidizing the proteins in the cells of the residue or in microorganisms.
They are non-toxic and non-tainting, and although corrosive in concentrate form, when used at the correct dilution are not. Acids and alkalis can be detected chemically, are fairly stable, and are bio- degradable. They should never be used in conjunction with halogen- based compounds as this would result in the liberation of chlorine gas, which is highly toxic.
Activity of disinfectants and sanitizers against microorganisms is often used in the sales literature for the compound. Most of these data are gathered through laboratory experiments, and often indicate the activity
(a)
(b)
(c)
Fig. 3.8. Mechanism of action of detergents. (a) Detergent molecules in solution are applied to the greasy surface; (b) the hydrophobic pole of the detergent molecules becomes buried in the grease; and (c) this pulls the grease off the surface and into suspension.
of the compound in vitro, against pure cultures of a particular organism.
However, when used in the field, the compound is often inactivated by organic material present on the surface to be cleaned, and the reduction in microbial numbers reduced from the expected 100,000-fold to only 100- fold or 1000-fold.
Further Reading
Denier, S.P. and Hugo, W.B. (1991) Mechanisms of Action of Chemical Biocides. Blackwell, Oxford.
Denier, S.P., Gorman, S.P. and Sussman, M. (1993) Microbial Biofilus: Formation and Control.
Blackwell, Oxford.