Food microbiology and hygiene

Food microbiology and hygiene

Surface: all welds should be continuous and smooth, a state that should be checked regulary and so maintained, to prevent any accumulation or food particles in cracks or seams which may otherwise develop.

Dead ends such as thermometer pockets or unused pipeworks T-picces must be avoided. The construction materials employed must be robust enough to prevent flexing or bending under procces conditions as this may create hollows where foods or cleaning fluids can accumulate. Debris tends to adhere to protruding  bolt threads, wing nuts, pot rivets and screws, and these should be avoided where possible in ood contact areas. Where construction necessitates some from of bolting the bolt head should preferably be sited on the product side (CFPRA, 1983). Where bolts are used there is always the possibility of a crevice being formed at the junction between the bolt head and the metallic surface of the vessel and this must be avoided by using durable plastic or similar washers. Nuts should always be of the domed type if situated on the product side.

7.5 EASE OF DISMANTLING AND REASSEMBLY OF EQUIPMENT

Whilst both the earlier FMF/FMA principles (section 7.1) and the 1989 machinery directive (section 7.2) allude to the need for easy dismantling of equipment for cleaning purposes, far too little attention has been paid to this crucial factor. Even with well - designed equipment it is possible for bacteria to build up during a procces run and if this build up is accompanied by variations in the residence time of food material a deterioration in the bacteriological quality of the food is inevitable. It is obviously important to minimize increases in bacterial numbers during processing and every opportunity should be taken to use the various break periods for essential cleaning work. Even the short 10-15 min break should be capable of being utilized to clean those equipment surfaces and parts regarded as hygienically hazardous ; the cleaning of all surfaces in contact with food should be feasible over the longer break periods.

Unfortunately it takes hours to dismantle many machines for cleaning purposes, complex tools are frequently required and, as a result, cleaning is often delayed. Stripping, cleaning and re – assembly must be made as simple as possible so that those surfaces and parts exposed to hazardous bacterial accumulation can be cleaned within 15 min. to facilitate this aim the number of working parts in food processing equipment should be kept to a reasonable minimum. However, rapid cleaning also entails convenient handling and hen ce constraints such as the weight and dimensions of individual parts must be borne in mind. Ideally components that require frequent cleaning should be provided to hold dismantded components off the flor. Quick release devices, e.g. captive bolts with coarse threads, should be used to facilitate cleaning ; alternatively, clamped joints (fig 7.1) may be used and one of their advantages is that they overcome the bacteriological hazards associated with screw threads mentioned earlier. Whatever quick release devices are usued it is important to unsure that only the simplest of tools are reuired, if any, in the dismantling and re-assembly of the equipment.

It may be pointed out here that faulty equipment design is, in part, responsible for large numbers of metal-in-food complaints. As there is often a plethora of nuts, bolts and screw to unfasten when dismantling certain items of machinery the cause of these complaints can be easly understood and traced; steps should be taken to rectify the faults in the interests of hygiene and common sense. It must also be emphasized that equipment designed for simple and speddy dismantling and cleaning is going to be cleaned more enthusiastically and efficiently than equipment that proves tedious and difficult to handle.

Larger parts of equipment must be also be designed so that cleaning, inspection and maintenance are facilitated. All parts requiring cleaning should be cleanable within an hour. Heavier components may be more suitably moved by some form of hoist, on safety grounds, as workers should not have to stuggle with parts that are difficult to handle.

In general, equipment used in batch processing is simpler than that used in continuous processing and the former should therefore be easier to design for ready access and cleaning. However, there are many items of equipment (e.g. meat slicing machines, mincers, cream dispensers) where bacteriological build up is rapid and where cleaning difficulties arise because failures; it is axiomatic that preffered models must be easly cleanable.

There is no doubt that clean-in-place (CIP) techniques will become more widespread in the future and where prolonged or continuous processing is performed CIP is essential. Until recently these techniques have been used almost exclucively for liquids and pipework but continuous cleaning devices for solid food processing equipment are being introduced. There is no doubt this welcome innovation will, in time, become the norm. some increase in the price of equipment must be anticipated but if labour costs are reduced an overall saving should be made (Holm, 1980).

7.6. ACCESSIBLITY AND THE SUPPORTING FRAMEWORK

Much of what has been said in the previous section is pertinent to the problems of accessibility of surfaces and components of food processing machinery. This issue has been discussed before but, for convenience, that main points are reiterated; normally equipment should be sited at a distance of ca 100cm from the nearest ceiling, wall and adjacent equipment although greater gaps may be required; in addition, equipment should be raised at least 20cm off the floor to facilitate cleaning, inspection and maintenance.

Easy acces is also helped by reducing floor and wall mountings and supporting framework to a minimum. Framework should be made of circular cross – section tubular steel rather than angle or channel iron as cleaning of the former is easier, it has no horizontal surfaces to collect dust and debris, corrosion is reduced and, because it is stonger and lighter, less supporting framework may be needed. All framework should have the ends welded or otherwise sealded throughout its length to facilitate cleaning.

Supports for heavier  floor – mounted equipment should be scaled to the floor so that food debris and pests are excluded and the edging to the seal should be coved to prevent debris accumulating. Where legs are used to support equipment they should be made of tubular steel which should be scaled or have ball feet fitted. The minimum number of such legs should be used and cross - bracing should likewise be reduced to a minimum; a single pedestal floor mounting is to be preferred.

Larger food processing plant such as air driers and cooling tunnels must include entry portals permitting easy acces for maintenance and cleaning personnel; such portals should be at least 60cm in diameter. Taller equipment such as spray driers often presents difficulties but easy and safe entry must be ensured through the provision of ladders or catwalks.

It is important to ensure that catwalks are constructed so that debris cannot be transferred from footwear to underlying equipment or food; thus decking should be contructed from suitable non-slip solid plate rather than mesh and the plate should be angled to incorporate a kickstop (Fig. 7,.2.) stairs, too, should conform to the same standards and protective backplates may be required near food lines (fig. 7.2.)

7.7. EXTERNAL SURFACES

External surfaces which do not come into contact with foods should be corrosion resistant, smooth, easily cleanable and free of protruding parts and crevices where debris might accumulate. Horizontal surfaces should be avoided where possible but if necessary such surfaces should be kept to a minimum and be readily accessible for cleaning puposes. Cheaper grades of stainless steel are often preferable as external surfaces but painted surfaces may be in close proximity to or directly over foods being processed.

Drainaged systems from equipment should be designed to prevent splashing and be readily cleanable and drains should be sloped so that efficient discharge is maintained. Drip pans and catch trays for spilled food material may also be required which should be easily  removable and cleanable.

So far the general principles of food equipment design have been discussed and these principles apply, where relevant, to all the following items. Therefore only additional design features for specific equipment are now described.

7.8. DESIGN FEATURES FOR INDIVIDUAL  ITEMS OF EQUIPMENT

7.8.1. tanks, vats, etc

Tanks, vats and similar equipment must be constructed so that drains are placed at the lowest point. Thus if there is central drainage the base must be dished to drain to that point whilst if there is side drainage the base must be pitched to the outlet (Fig 7.3). on no account should pipes be joined to tanks so that pipe ends protrude into the tank it self  (fig. 7.4.).  such arrangements are good examples of potential growth pockets described earlier whilst corrosion could result from residual cleaning solution or water ; in addition , the angles between the pipes and body of the vessel make cleaning extremely difficult. At the risk of unnecessary repetition it might be worth emphasizing that junctions between a vessel and pipe must be smooth, flush and without crevices. These same remarks apply to temperature probes often used in this type of equipment ; the standard fitting for these probes frequently have small gap between the probe and the body of the coupling where food can accumulate. Improved drainage and cleanability is achieved by mounting probes in a……………………………………………………

(Fig 7.1) a clamped joint used as a quick release device on a screw conveyor

(fig 7.2 ) A catwalk illustrating desirable features ; (a) non-slip solid plate decking ; (b) angled kick-stop (c) protective backplate

(fig 7.3) hygienically designed tanks.

(fig 7.4) poorly designed tanks