Problems caused by microbial contamination of foods tend to be expensive, particularly if these result in consumer recalls. As a result of the development and application of increasingly mild preservation technologies, processed foods become more sensitive to microbial (re)contamination, requiring greater control of the manufacturing process. One way to achieve this added control is to "build in" hygiene into the equipment used in the food manufacturing facility from the start.
The hygienic design of equipment plays an important role in controlling the microbiological safety and quality of the products made.
A hygienic factory should prevent products from having high microbial counts, from containing toxins of microbial origin, and from containing residues of chemicals used for cleaning and disinfection. In addition, the hygienic facility should prevent food from being contaminated with other non-food substances, such as lubricants, coolants and antimicrobial barrier fluids, as well as from containing foreign bodies, such as pieces of metal, plastic, packing material and insects or other vermin, or parts thereof.
This may appear a complex task, but with increased activity by international standard-setting organizations more specific and workable information on this topic is now available to the food industry.
HACCP is the Hazard Analysis Critical Control Points system that was developed to ensure the safety of food for United States astronauts nearly 30 years ago.
The Hazard Analysis and Critical Control Point (HACCP) system is internationally accepted as the system of choice for food safety management. It is a preventative approach to food safety based on the following seven principles:
- identify any hazards that must be prevented eliminated or reduced
- identify the critical control points (CCPs) at the steps at which control is essential
- establish critical limits at CCPs
- establish procedures to monitor the CCPs
- establish corrective actions to be taken if a CCP is not under control
- establish procedures to verify whether the above procedures are working effectively
- establish documents and records to demonstrate the effective application of the above measures
The HACCP approach provides a systematic way of identifying food safety hazards and making sure that they are being controlled day-in, day-out. This involves the following four steps: Plan, Do, Check.
Following the Legislative Order No.155/97, certain European Directives concerning food hygiene have been introduced in Italy and on 28 June '97 HACCP (Hazard Analysis and Control Critical Points) regulations regarding the health and hygiene prevention system came into force. The general obligation is that of guaranteeing the hygiene of the food in the treatment phase.
SCFN units are manufactured in accordance with HACCP guidelines.
There are several aspects of designing hygiene into equipment that should be considered by the food processor before reengineering or introducing process equipment into the plant. In general, construction materials that may come in contact with food should not be able to make a food product toxic. Equipment must be designed to be self-drainable to make it possible to remove all residues of products and chemicals.
To be cleaned without difficulty, surfaces must be smooth and free from crevices, sharp corners, protrusions, and shadow zones. When surfaces are not clean, microorganisms may be protected from destruction by heat or chemicals. Selected criteria and basic requirements for a variety of hygienic equipment characteristics provide a fundamental overview of areas that can be addressed by food manufacturers:
Material of construction
Materials used for the construction of a food processing plant must fulfill certain specific requirements. Product-contact materials must be inert to the product under operating conditions, as well as to detergents and antimicrobial chemicals (sanitizers) under conditions of use. They must be corrosion-resistant, mechanically stable, and such that the original surface finish is unaffected under all conditions of use. In addition, non-contact materials shall be mechanically stable, smoothly finished and easily cleaned. We use only stainless steel grade 300 family. The reinforcement in plastics and elastomers should not be allowed to contact the food product.
Product contact surfaces should be smooth enough to be easily cleanable. The roughness (or smoothness) of a surface usually is expressed in µm, as Ra-value. Generally, the cleaning time required increases with surface roughness. The American 3-A Sanitary organization and the EHEDG specify that food contact surfaces have a maximum roughness of Ra = 0.8 µm. Our maximum roughness is <= Ra 0.8 µm. To achieve this quality of surface, polishing or other surface treatment may be required. Cold-rolled stainless steel sheet material, used for vessels and for piping, usually has an Ra-value between 0.2 and 0.5 µm, and thus, further treatment is not needed. This our case as we use high pressure piping. According to the EHEDG, rougher surfaces can be acceptable if tests have shown that the required cleanability is achieved. Porous surfaces usually are unacceptable. To be cleaned without difficulty, surfaces must not only be smooth but also free from crevices, sharp corners, protrusions and shadow zones. This applies not only when equipment is new, but during its entire functional lifetime.
Crevices cannot be cleaned, and as such, will retain product residues that may effectively protect microorganisms against inactivation. In some cases, crevices are unavoidable. This may be the case if slide bearings must be in contact with product; for example, as bottom bearings of top-driven stirrers or as bearings in scraped-surface heat exchangers. The presence of slide bearings should be considered when writing procedures for cleaning and disinfection.
These procedures may require instructions for both partial or total dismantling of equipment, or for increased cleaning times.
In most cases, crevices are the result of incorrect choices when designing (or selecting) equipment. When parts of equipment must be mounted together, metal-to-metal contacts (other than welds) must be avoided because they leave very narrow and deep crevices.
Elastomers should be used between metal components, but not in the form of O-rings in standard O-ring grooves, as this, too, will create crevices. The elastomeric material must be mounted in such a way that the seal is at the product side and excessive compression is prevented to avoid destruction of the elastomer. This can be achieved by including design features that align the surfaces of the various parts and provide a metal stop. We use only FDA approved seals, EPDM end PTFE.
The use of screw threads and bolts in the product area should be avoided. Where unavoidable, the crevices created should be sealed, at minimum. In our design no screw threads are in contact with the product.
Sharp corners in the product area should be avoided. Exceptions are constructions where the sharp corner is continually swept, such as in lobe pumps. Welds should not be made in corners, but on the flat surfaces, and must be smooth. No welds parts are in contact with the product.
There is a significantly reduced transfer of energy to the food residues (soil) in dead areas in process equipment that is placed outside of the main flow of cleaning liquids than there is to the soil in the main flow. Such areas are difficult to clean, and therefore, should be avoided. If unavoidable, their presence should be taken into account when devising the cleaning procedures. Typical shadow zones, for example, can be found in the legs of T-pieces in pipelines, which are used to mount sensors such as pressure gauges. No dead line are present in our design. Pressure gauges are installed with membrane separators not to have any dead leg.
Drainability of equipment and process lines
To make it possible to remove all chemicals from process equipment, the equipment must be designed to be self-drainable. Thus, surfaces and pipes should not be completely horizontal, but slope toward drain points. There should be no ridges that may hamper draining.
Where it is not possible to build equipment in such a way that proper draining is possible, procedures must be designed to ensure that residues of cleaning and disinfection liquids can be removed in another way. The method used should be well documented with clear instructions.
Draining also is important, even in cases where no chemicals are used, because many microorganisms can easily grow in residual water, needing only minute amounts of nutrients to multiply. Using supercritical fluids the pipe cleaning procedure is different than usual as no water is involved in the process. In addition, the presence of carbon dioxide as main solvent do not promote the growth of bacteria in the circuit.
Top rims of equipment
The design of the top rims of product-containing equipment must avoid ledges, where product can lodge and that are difficult to clean. Open-top rim design must be rounded and sloped for draining. If the top rim is welded to the wall, the weld must be flush and polished to provide a smooth surface. In this case, the rim must be totally closed.
The weld must be continuous and any holes must be sealed by welding, gaskets or plastic caps. All our vessels are not open but closed with a lid. Proper FDA approved gaskets are used to assure a good sealing.
Mandoor covers intended to protect the food products may accumulate dirt, which will enter the product in the vessel when the lid is opened.
Policy should specify that no tank is opened during production unless absolutely necessary. No mandoor cover exist in our design.
Shaft passages and seals
Shaft passages and seals may leak product to the outside of the line. Microorganisms may then multiply in the product and grow back to the product side. In the case of dynamic seals, such as those for shafts of valves, pumps and mixers, the movements of the shaft will assist the transfer of product to the outside and the transfer of micro-organisms to the product side. This applies to reciprocating shafts, and to a lesser extent, to rotating shafts, the latter always displaying some axial movement.
Reciprocating shafts can be sealed by means of flexible diaphragms or bellows. To prevent the ingress of microorganisms in rotating shafts, double seals with microbiocidal barrier liquids should be used.If not replaced in a timely manner, however, such barriers may become a growth medium for microorganisms. We use high pressure valves and seals. No leaks are possible during the process without the operator be informed immediately by the PLC control system.
Hygienic pipe couplings
Pipe couplings are the most frequently used elements of modern food processing equipment. Wherever connections are made between plant elements (e.g. pumps, valves, filters, vessels), a dismountable joint creates possibilities for maintenance, quick replacement, or changes in the processing sequence or product flow route.
Because pipe couplings are typically mass produced, they were among the first items to be standardized. The basic designs specified in the most important standards currently used in Europe are now 30-35 years old. As the development of products and processing methods has resulted in more sensitive products and more severe process conditions, in many cases pipe couplings are operating at the limit of their capabilities, with increasing risk of failure from hygienic as well as mechanical points of view.
This increasing risk and the related failures have prompted equipment users and manufacturers to design improved couplings. Thus, almost every major equipment supplier now has their own type of coupling, reducing equipment versatility and increasing costs to
users and manufacturers.
Hygienic design of closed equipment for the processing of liquid food
It is strongly recommended that joints are avoided where possible. For piping, bending of the pipe is highly preferable over the lise of prefabricated bends with couplings. If pipe bending is not possible, welding is the preferred method, provided that the welding is done correctly, to ensure a smooth and continuous weld. Where detachable joints are necessary, they should be sealed by elastomers.
Compression of elastomers, overcompression of elastomers may affect the hygienic characteristics of equipment in two ways. Firstly, overcompression may lead to destruction of the elastomer, particularly if the overcompressed elastomer is heated (such as during pasteurization or sterilization).
The elastomer may hecome brittle and fail to provide the required seal, while pan of the elastomer may contaminate the product. Secondly, overcornpression may lead to protrusion of the elastomer into the equipment, thereby hampering cleaning and draining. Undercornpression too is highly undesirable as it may lead to crevices and fail to provide a reliable seal even when it is not visibly leaking. the seal may permit the ingress of microorganisms.
Self-evidently, not only the dimensions of the metal components, but also those of the gasket must be correct,
ensuring adequate compression at the product side, taking into account differences in thermal expansion under all operation conditions (cleaning, pasteurization or sterilization. and processing).