Looking out for certain features of weighing equipment can help food manufacturers maximise their return on investment, and minimise the risk of contamination. Isaac Leung writes.
Food contamination can occur via any number of vectors, so constant vigilance is required during every step of the food supply chain.
One oft-overlooked source of food contamination is weighing equipment, a fundamental part of portioning in food processing.
Current international standards which govern hygiene in relation to weighing equipment in the food industry include the European Hygienic Engineering & Design Group (EHEDG) guidelines, BRC Global Food Standard, SQF program, ISO 22000, and the NSF 3-A/ANSI 14159-1 standard.
Locally, the Australia New Zealand Food Standards Code relating to Food Premises and Equipment stipulates that equipment needs to be designed, constructed, located and installed to ensure there is no likelihood they will cause food contamination, and can be easily and effectively cleaned.
In the case of food contact surfaces, for example, where a scale has foodstuff set on it during the portioning process, the rules are even stricter: in addition to the above, they need to be able to be sanitised, and be unable to absorb grease, food particles and water, and made of material which will not contaminate food.
Similar requirements can be found in the policies of food retailers. For example, Woolworths’ Quality Assurance Standard pertaining to Manufactured Foods require well-documented procedures for the microbiological and chemical cleaning of processing and handling equipment. These cleaning procedures are backed up by visual inspection, residue testing, and quarterly microbiological swabbing of surfaces and equipment.
Woolworths also requires planned preventative maintenance programs which include clean in place (CIP) operations utilising documented chemicals, hot water and energy like scrubbing or high pressure hosing.
According to Phil Hyland, project manager at Mettler Toledo, the last three to four years have seen a tightening of hygiene controls as a number of high-profile food contamination cases have emerged globally.
Weighing equipment manufacturers have kept an eye on these stringent demands, and designed their equipment to be correspondingly easier to clean, with less food traps and areas which could become sources of cross-contamination.
By virtue of their function, weighing equipment consists of a mix of direct food contact surfaces and non-contact surfaces.
On a scale, non-product contact surfaces can include the terminal, housing, and feet, but these can cause indirect contamination. Depending on the type of food being weighed, the feet of scales can also be in direct food contact.
Contact surfaces are defined as surfaces in direct contact with food residue, or where food residue can drip, drain, diffuse or be drawn. The scale platform is the most obvious direct food contact surface.
These surfaces need to be smooth, non-porous, non-absorbent, impervious; free of cracks, crevices, pitting, flaking, and chipping; corrosion-resistant; durable and maintenance-free; non-toxic, non-contaminant; cleanable and non-reactive.
The standard material for contact surfaces is stainless steel, which is corrosion-resistant and durable. 316 steel is preferred, while 304 stainless steel is also adequate.
To attain the requisite hygiene ratings, the surface needs to be polished to a smoothness of 0.8 micron or better. Rougher surfaces prevent effective cleaning as microorganisms become trapped in the surface, becoming a bacteria trap.
Of course, cleanability can also be dependent on the finishing technology, which can affect the surface topology.
Where other materials are used, plastics should be food grade, and smooth ceramics is also a common material.
According to Hyland, the common approach to use silicon-based potting material to protect sensitive parts of weighing equipment, such as the load cell, is insufficient for food-grade equipment. Certain cleaning products can shorten the life of silicon potting materials. A better approach is to protect the load cell with a welded, IP69 rated seal.
Designed for cleaning
The ability for equipment to handle heavy washdowns is one of the things which differentiates food-grade industrial weighing systems from, say, a kitchen scale. But Hyland says customers who only focus on the washdown capabilities of equipment may be overlooking other important factors.
“They often haven’t looked at the ability to clean the equipment properly, such as ensuring there are no food traps,” Hyland explained. “The converse applies: you could have a machine which is open and able to be washed down but the equipment eventually suffers from the cleaning.”
“We’re looking for something that can be cleaned to a satisfactory standard and yet be able to withstand that process.”
Equipment which is poorly designed may require more severe and prolonged cleaning. Aggressive chemicals and longer clean/decontamination cycles increase maintenance cost and downtime, and in the long run, can reduce the life of the product.
To avoid food traps, equipment should not have sharp corners and crevices, and mated surfaces should be continuous and substantially flush. Construction should allow easy disassemble for cleaning and inspection.
Internal angles should be rounded to standards-specified radii. Most standards specify the avoidance of sharp corners, less than 90 degrees.
Particular features which allow for easy cleaning include full stainless steel construction, smooth surfaces, continuously welded and completely closed columns with no disturbing cables, and ingress protection of IP68 or IP69K.
“IP69K sealing gives our food industry equipment very good protection against hot, high-pressure hosing,” Hyland said. “When you are in a meat room or a food processing area, the temperature often changes. If a freezer comes on, for example, you can have a large change in air temperature.”
To combat condensation within equipment due to temperature changes, the machines should be well-sealed, and properly vented.
“Food equipment in high-condensation areas will have Gore-Tex vents, which allow a balance of air pressure, so it doesn’t try to suck in moist air, but also does not allow moisture in through the vent,” Hyland explained.
While the design of equipment is an important aspect of food safety, food safety auditors say many manufacturers often spend millions of dollars on equipment, only to find themselves out of step with their core customers’ requirements.
Standards like the Woolworths Quality Assurance Standards and the Coles Housebrand Supplier Program specify a comprehensive set of requirements, which relate to factors beyond equipment design like equipment placement, calibration, cleaning, interfaces with other equipment, and data retrieval and analysis.
By having a good understanding of all aspects of these requirements, in addition to equipment design, food manufacturers can minimise the risk of contamination, and ensure they are compliant with relevant standards.