March 1, 2008
Catching the Pieces
By Tom Wray, associate editor
Metal detection and X-rays help finish a program of food safety on the processing line.
The manufacture of meat products can have some bumps in the process. Even with the best maintenance, there are times materials can get into the product. It’s metal detectors that help ensure the safety of the products produced.
The use of metal detection in food processing began just after World War II in the United Kingdom. At that time, it was used to catch any ammunition, sometimes live, that had become mixed with food going into processing. These days, the material that could be caught is just a bit more mundane.
“There are a number of things that are possible,” says Oscar Jeter, national sales manager for Mettler-Toledo’s metal detection division in Tampa, Fla. “Some of the items that can find their way into the product include hypodermic needles used on cattle, birdshot from hunters in the fields and pieces of the machines used in processing,” he says “Even as equipment is maintained, at some point, parts of it will come out — perhaps a bit of saw’s tooth or small bit of a knife. Other contaminants could also come from general maintenance of the facilities such as metal shavings and wire.”
Ray Spurgeon, product manager at Erie, Pa.-based Eriez Magnetics, says that even personal protective items such as metal detectable earplugs, rubber gloves and bandages are now being detected and removed from the process stream. These items are seeded with additives or steel spheres.
“One of the things you have to realize, even if you install a detector, without a program to control items, you won’t find all the metal pieces,” Jeter says. “It’s just one tool in the program.”
The use of X-rays has also become more common. Terry Woolford, vice president of sales and marketing for Alcoa, Tenn.-based Smiths Detection, says that X-ray inspection began in the mid-1990s as a response to industry calls for more comprehensiveinspection as required under Hazard Analysis Critical Control Points (HACCP) procedures.
“In these very early days X-ray systems were targeted atdifficult metal detect applications including: products packed inaluminum foil, metalized film wrapped products and products with a large product effect and variability caused by salt/moisture content and temperature,” says Woolford. “X-ray systems are not affected by thisproduct variability and as such improved upon sensitivity —detecting smaller metal particles.”
How it works
Spurgeon explains that there are some challenges to getting the best use of a metal detector on the line.
“Meat products are conductive and have an effect on a metal detector’s performance, particularly to stainless steel,” he says. “This is known as product effect. The primary reason for this is that stainless steel and meat products look very similar to a metal detector — they share the same phase angle. This phenomenon can be best explained by thinking of phase angle in terms of a clock.”
Spurgeon explains that meat products “phase out” at 11:25 on the clock; that is to say the big hand is on the five and the little hand is between eleven and twelve. Stainless steel shares the same location on the clock, in terms of its phase angle, and therefore stainless steel is “masked out,” or hidden, by the meat product.
To overcome this limitation, he says, a metal detector must have the proper vertical phase setting to avoid the product tripping the metal detector.
“It requires sophisticated electronics that employ state-of-the-art digital signal processing to differentiate the two,” he says.
The use of X-rays runs into a somewhat different problem. There, it is the density of the material that makes a difference.
“One of the large interest areas in the meat industry is the detection of bone, while X-ray can find embedded bone fragments, the bone fragment must be calcified to be detectable,” says Woolford. “Gristle and cartilage are therefore not detectable, as they are largely the same density as the meat product.”
The low density of aluminum can also present challenges.
There are some new technologies available in the latest metal detectors to help overcome some of these issues.
“One of the newest arrangements we have is running many different products on a single setting,” says Jeter. “It saves time from having to change from one setting to another. There’s not as many people in the plants as there used to be. If you can have the metal detector run on one setting, that’s a great advantage.”
Spurgeon says that the use of digital signal processors to gather more information about the product being scanned is also at the forefront. The ability to retrieve more information and interpret it will make metal detectors more reliable.
Jeter goes on to say that the basic performance of new metal detectors has also been improving. The newest version of his company’s metal detector can find smaller particles than older models. He says it’s hard to say exactly what the smallest-sized particle the detectors can find is.
“It depends on the metal detector and the product scanned,” he continues. “It’s easier to find it in a smaller sample and in a drier product. But certainly metal detection in the area of less than .5 millimeters is quite possible, again depending on product and size of the detector.”
He says his company continues to try to make the detector better, to find smaller and smaller particles. Mettler-Toledo is also striving to make them more automatic as well. That’s what processors want, Jeter says.
Woolford says that new advances in X-ray technology include fat analysis based on dual energy and it enables importers and exporters to know the chemical lean and fat content of 100 percent of their meat, accurate to one percent. This eliminates fat claims and enables processors to buy and sell meat on a point-to-lean basis, rather than relying on inaccurate visual lean.
X-rays can be used throughout the process.
“We routinely inspect many incoming goods to prevent the loss of finished product and packaging waste,” says Woolford. “In process, the X-ray can provide valuable throughput data and can improve process efficiency. For example one bread processor checks the shape, weight and size of dough prior to baking, saving energy wastage on cooking misshapen product and reducing product waste.”
Jeter says consumer protection and brand protection are foremost reasons for the use of metal detection. In addition to that, within the process, metal detection can be used for machinery protection. As an example, a processor could detect meat blocks heading to a grinder, where a piece of metal could damage the grinder. Even if the grinder weren't damaged by the piece of metal, it could create smaller metal particles that would be harder to detect downstream.
“Metal detectors can be used to inspect product that is on a conveyor belt [after an extruder], on a packaging line, or on a pipeline,” Spurgeon says. And as the technology emerges further in both standard metal detection and X-ray systems, it appears that soon, there will be nothing this technology couldn't do to protect product from foreign objects.
New Metal Detection guide
Mettler-Toledo Safeline has recently produced a guide to metal detection, designed to help the global food and pharmaceutical industries.
The guide is titled, “Reduction of Metal Contamination — Building an Effective Program.” The company says the new guide replaces the original “Safeline Guide to Reducing Metal Contamination.”
The new guide updates theinformation and is available for free from Mettler-Toledo. It covers the creation, implementation and maintenance of an effective metal-detection program.
“The need for metal-detection systems in the food and pharmaceuticalindustries is recognized by most manufacturers and processors as an essential area of focus in any efficient quality regime,” says Joe Gianfalla, marketingmanager for Tampa, Fla.-based Safeline. “In today’s increasingly competitivemarketplace, new legislation, the tightening of industry standards and the growth of regulatory bodies has meant that the importance of being able to demonstrate that an effective metal-detection program is in place has escalated considerably.”
Chapters one through four provide the basics of how metal detectors work, an explanation of important design features, an insight into those factors that could potentially limit performance of the equipment, and the integration of metaldetectors with effective rejection systems. The other chapters provide details into building a program. Issues covered include the reasons for metal detection, the prevention of contamination, selecting control points in the production facility, understanding operating sensitivity, and installation and commissioning.
“Reduction of Metal Contamination — Building an Effective Program” includes information regarding the elements of equipment testing and validationprocedures. These topics include: how to conduct tests, the correct handling of suspect and rejected product, the analysis of data and the electronic collection of data in enterprise-wide management information systems.