The need for effective cleaning and sanitation regimes in food production areas has never been greater. Longer, more flexible, production runs, the food safety and hygiene requirements of legislation and customers, environmental concerns and energy costs have all steadily increased the pressure on cleaning schedules in recent years, yet the basic technology available has changed comparatively little. Technological development in cleaning and sanitation has been largely by evolution rather than revolution. Nevertheless, some recent developments have the potential to make a significant impact on factory hygiene and novel materials could make cleaning in the food factories of the future a very different operation.

Despite the development of sophisticated food safety management systems over the last 30 years, one of the most important requirements for a safe food manufacturing operation is still very simple. Keeping production areas and processing equipment clean remains a key aspect of factory hygiene and food safety control. This principle is generally enshrined in modern food hygiene and safety legislation and a requirement to have an effective cleaning and sanitation schedule in place is virtually universal. The ISO 22000 and PAS 220 international food safety standards, food safety certification schemes, such as the BRC Global Standard, and retailers’ in-house standards are typically more prescriptive and take the requirements for effective cleaning further still.

No matter how effective other control measures are and no matter how rigorously the HACCP plan is implemented, dirty surfaces and dirty equipment always mean a risk of contamination. For an example, one needs look no further than a Listeria outbreak that killed 23 people in Canada in 2008. The outbreak was linked to ready-to-eat cooked meats from a large manufacturer and the source of contamination was eventually traced to meat slicing machines on the production lines. Although the company concerned was generally regarded as operating to very high standards of safety and hygiene, the cleaning and sanitation of these machines was found to be inadequate, allowing a build up of microbial contamination during production. Unknown to the company, this was not completely removed by the cleaning procedure, which did not require the machines to be dismantled before they were cleaned.

New pressures on cleaning schedules

The same outbreak also helps to explain why cleaning and sanitation schedules are coming under more and more pressure from the demands of modern food manufacturing. One of the reported reasons why the slicing machines were not routinely dismantled for cleaning was that it was thought to take too long, considerably delaying the resumption of production. Thirty years ago, many food production lines operated only for 12 hours or so each day and probably shut down at weekends. This allowed plenty of time to clean the environment and equipment before the next run. Today, in the interests of efficiency, managers want lines to run for much longer periods, often seven days a week. Cleaning has to be carried out within a diminishing window of opportunity. Furthermore, modern processing lines, especially in the chilled sector, need to be more and more flexible to cope with ever-changing production planning schedules. This means that cleaning has to be equally flexible in order to cope with such a fluid situation.

Time pressures are not the only concern for hygiene managers. Budget cuts and the rising costs of energy, cleaning materials, water and effluent disposal mean that cleaning and sanitation procedures must be as efficient as possible in their use of resources. Environmental issues are also becoming increasingly important. Many of the chemicals traditionally used in food plant cleaning are quite aggressive and cannot necessarily be released straight into the water treatment system. Potential environmental damage caused by strongly acidic or alkaline chemicals in waste, or by high concentrations of biocides is not an acceptable by-product of food production and is now strictly regulated by environmental authorities.

Steady progress in design and technology

Over the last ten years or so, these trends have necessarily driven the development of cleaning and sanitation technology, but that development has generally taken the form of small incremental improvements rather than great leaps forward. Plant design has certainly improved, partly as a result of initiatives like the European Hygienic Engineering and Design Group (EHEDG), which issues guidelines for the hygienic design of many types of food processing equipment. EHEDG guidelines seek to encourage the development of equipment designed to eliminate potential contamination and facilitate effective cleaning. In the past, some food processing equipment has been virtually impossible to clean properly without being completely dismantled, but modern machinery should be designed with easy and effective cleaning in mind. Many equipment suppliers have had their products certified to show that they meet EHEDG guidelines.

The layout of newer food factories has improved, particularly in the high-risk chilled sector, to allow easier access to equipment and help make cleaning faster and more effective. Clean-in-place (CIP) systems have also contributed significantly to better plant hygiene, especially in larger, partly automated processing lines. The suppliers of cleaning and sanitising chemicals have steadily improved their products to make them more effective and efficient, while chemical dispensing systems have improved too. Developments like cleaning foams and gels enable longer contact times with equipment and surfaces during open plant cleaning and reduce the quantities of chemicals required. Many food manufacturers have taken the opportunity provided by these improvements to develop the much more effective, flexible and rapid cleaning schedules demanded by modern food production.

Taken as a whole, these developments add up to a major change in plant cleaning and sanitation, but it would be hard to point to one technological change as the key to improved cleaning. This has led to a situation where progress has slowed as existing technologies have been developed to their full potential, while the pressures on plant cleaning continue to grow. Fortunately, there are existing technologies, largely developed for use in other industries, which may be able to provide practical solutions.

Cryogenic cleaning

An example of such a technology is the dry ice blasting or cryogenic cleaning method first developed in the USA in the late 1980s. The technique was originally intended as a less damaging alternative to sand- and bead-blasting techniques for removing paint and coatings from surfaces. It found many applications, from the electricity generating industry to paper manufacturing, but over the last ten years cryogenic cleaning has attracted increasing interest from the food industry.

Cryogenic cleaning works by blasting small pellets of solid carbon dioxide (dry ice) onto a surface at high velocity. This has two effects, one thermal and the other mechanical. The pellets are delivered to the surface at a temperature of -78.5^oC, creating a localised thermal shock, which helps to break the adhesion of any residues on the surface. The impact of the pellets also creates a mechanical separation effect between residues and the surface, an effect amplified by the large pressure changes caused by the rapid sublimation of solid CO₂ to the gaseous form.

The process has two important advantages over other particle blasting methods, both of which make it suitable for use in the food industry. The first is its non-abrasiveness, which allows treatment of delicate surfaces without damage. The second is the complete sublimation of the blasting medium to a gas. This means that the process does not leave any solid residues other than a few particles of the removed soil, which can easily be removed by suction. Since no water is used, a clean dry surface is left, and the process can be used to clean surfaces close to electrical equipment, which could easily be damaged by aqueous cleaning methods.

Cryogenic cleaning is particularly suitable for cleaning protein and other residues from ovens, mixers, moulds, conveyors and packaging machinery, where cleaning is otherwise a labour-intensive manual process, or access is difficult without dismantling equipment. It is also a valuable technique for use in ‘dry’ processing areas, where the use of wet cleaning is not appropriate. It has found applications in the baking sector, especially in the USA, but is also used by confectionery and soft-drink manufacturers. A research project funded by the UK Food Standards Agency also showed that the process could be used to clean and sanitise a variety of surfaces in meat and poultry processing plants. Significant reductions in the population of microbial pathogens on plastic, stainless steel and ceramic surfaces were demonstrated.

Cleaning by this method is claimed to be much faster and more effective than conventional manual cleaning. The main drawback is cost, although prices of dry ice blasting machinery and dry ice pellets have dropped considerably over the last ten years. There are now many specialised cleaning contractors with experience of using cryogenic cleaning equipment in food factories and the equipment is also commercially available from suppliers such as Cold Jet in the USA and Aquila Triventek A/S in Denmark.

Whole room disinfection

Whole-room disinfection is a hygiene technology that could make a significant contribution to food safety, especially in the high-risk chilled sector. Conventional sanitation techniques typically involve applying a suitable sanitizer to food contact surfaces during the final stages of the cleaning process after all the soil has been removed. This is a well established and effective method of minimising microbial contamination on surfaces and limiting cross contamination. What conventional sanitising methods cannot easily do is tackle contamination elsewhere in the production area, which might act as reservoirs for microorganisms to recontaminate processing equipment and surfaces. Listeria presents a particular problem in this respect. Research has shown repeatedly that particular strains of Listeria monocytogenes can become established in food production areas. Once this happens they can be extremely difficult to eradicate. Drains and other hard to reach areas can harbour contamination during the most rigorous cleaning and disinfection and food contact surfaces can soon become recontaminated during production.

One way of tackling this problem is to flood the entire production area with an antimicrobial compound in the form of an aerosol, vapour or gas, which can penetrate within equipment and treat all potentially contaminated surfaces at the same time. This technique is well known in the pharmaceutical and healthcare industries, but has so far not been widely used in food production. Nevertheless, as the technology for delivering whole-room disinfection has improved, so food industry applications have begun to become more practical. The UK-based Campden BRI food research and consultancy organisation has been investigating the effectiveness of several such techniques and has also reviewed all the available technologies. A recent project in collaboration with UK-based suppliers Steritrox and Bioquell has compared chemical fogging techniques with ozone gas and hydrogen peroxide vapour.

The project first looked at the effect of the three disinfection techniques against three common contaminants in food production areas, Listeria monocytogenes, Pseudomonas aeruginosa and Staphylococcus aureus, in the laboratory. Chemical fogging using proven biocides was an effective means of reducing contamination in the air and on horizontal surfaces – with an up to 6-log reduction in population in one hour – but its effect on vertical surfaces and underneath equipment was very limited. Hydrogen peroxide vapour (HPV) at a concentration of 20 g/m³ only gave a 3-log reduction with the three test organisms. Increasing the concentration to 40 g/m³ gave a 4- to 5-log reduction for Ps. aeruginosa and L. monocytogenes but did not reduce Staph aureus numbers any further. However, further tests with spores of Bacillus subtilis showed HPV to be more effective against bacterial spores, which are usually highly resistant to biocides. Ozone was found to be the most effective of the three disinfectant treatments against vegetative bacterial cells. At a concentration of 20 ppm, a greater than 4-log reduction was achieved for L. monocytogenes, with similar results for Ps. aeruginosa.

Reductions for ozone and HPV were found to be the same on vertical surfaces and the undersides of equipment as they were on horizontal surfaces, suggesting that both would be able to reach parts of the production area difficult to access by other means. Further field trials showed that a low concentration (80 ppm) of ozone applied periodically over three days produced an apparent downward trend in microbial counts on a pizza production line, though without any dramatic reductions. A longer trial suggested that a daily treatment with ozone at 80 ppm for 30 minutes could be an adequate replacement for conventional chemical disinfection, after appropriate validation. But to achieve large reductions (5-6 log) in numbers of Listeria and other pathogens in a single treatment would require a more severe treatment equating to at least 90 ppm for one hour.

Both ozone and HPV leave no chemical residues after use and so have an environmental advantage. There are also potential savings in water use and the cost of chemicals. Ozone is very unstable and must be produced at the point of use, but commercial mobile generation units are available for food industry applications. Mobile systems for HPV are also available and have been widely used to decontaminate clean rooms in the pharmaceutical and clinical sectors. The main disadvantage of whole room disinfection is the need to close off the space to be treated and exclude all staff until ozone or HPV in the air return to safe levels. But recent advances in ozone treatment claim to have reduced the period needed to achieve a safe level down to one hour. Recent reports indicate that a number of food manufacturers have shown interest in the technology, especially in the high risk cooked meat and fresh produce sectors. Where persistent contamination problems have proved difficult to control using existing technology, whole-room disinfection may prove to be the most effective solution.

The self-cleaning factory

While both cryogenic cleaning and whole-room disinfection are recent technologies that already exist and are in use, albeit to a limited degree, there are other intriguing developments that may have a much greater impact on cleaning and hygiene in food factories. A good example is provided by research into ‘self-cleaning’ surfaces for the medical device sector. A type of self-cleaning glass already exists and the use of nano-scale coatings and materials may allow the development of surfaces that simply cannot become soiled or contaminated because materials will not stick to them. It is possible to imagine food processing areas where all the food-contact surfaces are made from such materials, where cleaning of any kind is seldom necessary and production can continue for 24 hours a day. That is still some way off, but it is a real possibility.

Further reading

Campden BRI Review 63: Whole room disinfection – a review of current methods.