No need to look startled — cleaning and sanitation in food processing areas just needs good planning

Cleaning and sanitation of a process plant is one of the most critical aspects of food processing to ensure the health and safety of the consumer. Proper cleaning is essential for the production of high-quality food products, especially those with extended shelf life.

Cleaning-in-place (CIP) is now a very common practice in many dairy, processed food, beverage and brewery plants replacing manual strip down, cleaning and rebuilding of process systems. The primary commercial advantage is a substantial reduction in the time that the plant is out of production and the ability to utilise more aggressive cleaning chemicals in a contained environment that cannot be safely handled with manual cleaning.

The definition of CIP is given in the 1990 edition of the Society of Dairy Technology manual CIP: 'Cleaning in Place' as: “The cleaning of complete items of plant or pipeline circuits without dismantling or opening of the equipment, and with little or no manual involvement on the part of the operator. The process involves the jetting or spraying of surfaces or circulation of cleaning solutions through the plant under conditions of increased turbulence and flow velocity."

Design of cleanability

The design of the process plant must conform to all documented hygienic design standards. It is not usually possible to apply a CIP system to a process plant that was not designed for CIP in the first place. The materials of construction of the entire process plant must be resistant to the food and cleaning chemicals to be applied, and be non-toxic, smooth, non-porous and free from crevices capable of harbouring bacteria.

Materials of construction

The most common construction materials are stainless steels (notably grades 304, 316 and 316L) that have good resistance to corrosion in most environments, especially under acidic conditions and in wet washdown areas.

A clean-up process with a high chlorine-based agent requires special materials such as Teflon and PVDF, more commonly known as Kynar.

Seals and gaskets that are necessary to seal various metal parts need to be impervious to aggressive chemicals and high heat temperatures (eg, heat exchanger seals and pipe connections), and the effect that cleaning chemicals can have on them can destroy them over time, leading to unsafe practices and degradation of the seal that enables it to harbour microorganisms.

Elastomers and plastics must be resistant to the food product and the operational conditions in which the cleaning fluids are applied. It must also be demonstrated that there is no leaching of potentially toxic components from the elastomers and plastic materials; this often excludes many regular type plastics used as sealing materials. The most commonly used elastomers include nitrile rubber, EPDM (ethylene propylene diene monomer) for temperatures to 135°C (noting EPDM has poor resistance to oils and fats) and Viton. Also known as fluoroelastomer, Viton has excellent resistance to high temperatures but has reduced elasticity compared to EPDM and so requires more frequent replacement due to its poor memory.

All plastics and elastomer materials must be routinely inspected as part of a preventive maintenance plan and replaced at the first signs of brittleness. Brittleness causes a reduction of elasticity and eventually fails the ability to safely contain process fluids. Signs of discoloration are also indicators that seal failure is imminent. Incorrect sealing material may not have the temperature or chemical resistance required and should be avoided.

Surface finishes

A smooth surface is generally considered to be easiest to clean, while rougher surfaces require a longer cleaning time due to material adhesion to a rougher type surface. A surface roughness of no greater than 125 ra (roughness average) finish is required for FDA compliance and this finish standard is usually applied to a raw ingredient pumping process prior to pasteurisation; elastomer types are wide and varied, subject to product types being pumped.

High sanitation level pumps require a 32 ra finish and use elastomers such as Teflon, EPDM, Santoprene, Viton, Buna N and a stand that allows the pump to be flipped 180° for draining after the cleaning process.

Highest standard pumps are either EHEDG (European Hygienic Engineering Design Group) or the United States Three A authority. Both have the highest standards of design used in the food industry, including 32 ra finish, EPDM overmoulded diaphragms, EPDM seals or encapsulated EPDM/Teflon seals. Units must be fitted with a leak detector to shut down automatically in the event of a diaphragm failure to avoid product contamination and the stand must be able to rotate 360°.

USP Six is a pharmaceutical standard that has a 20 ra finish and must be stainless steel with Teflon elastomers only. The standard is typically associated with the manufacture of injectable and digestible products for human consumption. It is also a common pump type used in the manufacture of veterinary products.

The FDA standard allows for bolted construction design, HS, EHEDG, Three A and USP Six. All must use Tri-Clover clamps for ease of strip down and reassembly. The concept behind this is so the pumps can be pulled down and reassembled without the use of hand tools that typically mar the surface and can create imperfections that harbour bacteria.

Chemicals

The choice of chemicals is governed by the materials of construction of the plant. As mentioned previously, the most common material of construction is stainless steel, which is very resistant to most cleaning solutions (with the exception of high-chlorine-based solutions).

In the food industry, the most common form of fouling is the build-up of proteins in the system. These are removed by hot alkali (caustic soda) assisted by wetting agents that break up the protein into water soluble units.

Typically 2% caustic soda will be used at temperatures of up to 85°C. For high build of material on surfaces, solutions up to 4% can be applied. Milkstone and calcium deposits are easily removed by the use of a dilute acid being nitric or phosphoric, which is typically used.

Sanitation is achieved by the use of hot water, hypochlorite or one of the peroxide-based sterilising agents. If sodium hypochlorite is used for sanitising, the strength should not exceed 150 ppm free chlorine, the temperature should be kept below 40°C and the circulation time kept below 20 minutes.

Pumps for transferring the agent to the CIP system should be of PVDF (Kynar) construction.

Cycle times

The period of circulation depends on the degree of fouling and material build-up, taking into account the type of equipment being cleaned. Typically 20 minutes of caustic circulation is required for pipework and vessels. Pasteurisers and UHT (ultrahigh-temperature) plants which suffer from higher levels of fouling mainly due to the heat applied in the treatment of the food manufacturing process require up to 40 minutes of caustic circulation. Acid circulation is normally 10 minutes. Sodium hypochlorite should be kept below 20 minutes.

Recommendations

It is clear that within the food, beverages and pharmaceutical industry there are specific technical and engineering criteria that need to be observed to satisfy stringent sanitary requirements. These consist primarily of certain grades of stainless steel to be used with certain types of finishes and specific engineering design for ease of cleaning coupled with particular sanitising solutions and flush methods, including duration of flush times. It is recommended these be strictly observed to maintain health and hygiene for the consumer; this will also avoid potential litigation in the event of a contamination issue arising due to poor practices. Wise purchasing at the outset of equipment acquisition will avoid unnecessary additional cost; when the inadequacies of incorrect equipment are discovered this will lead to costly replacement.

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