Food Safety Magazine

Testing | December 2016/January 2017

Foreign Materials in Foods: Control and Evaluation

By Richard F. Stier

Foreign Materials in Foods: Control and Evaluation

If one goes to the website of the U.S. Food and Drug Administration (FDA) and searches for “defect action levels,” one will find the agency’s Defect Action Handbook. This handbook provides interested parties with a complete description of how defect action limits (DALs) are defined and what those limits are in foods. The following italicized paragraphs are cited verbatim from the handbook.[1]

Title 21, Code of Federal Regulations, Part 110.110 allows the Food and Drug Administration (FDA) to establish maximum levels of natural or unavoidable defects in foods for human use that present no health hazard. These “Food Defect Action Levels” listed in this booklet are set on this premise—that they pose no inherent hazard to health.

Poor manufacturing practices may result in enforcement action without regard to the action level. Likewise, the mixing or blending of food with a defect at or above the current defect action level with another lot of the same or another food is not permitted. That practice renders the final food unlawful regardless of the defect level of the finished food.

The FDA set these action levels because it is economically impractical to grow, harvest, or process raw products that are totally free of non-hazardous, naturally occurring, unavoidable defects. Products harmful to consumers are subject to regulatory action whether or not they exceed the action levels.

It is incorrect to assume that because the FDA has an established defect action level for a food commodity, the food manufacturer need only stay just below that level. The defect levels do not represent an average of the defects that occur in any of the products—the averages are actually much lower. The levels represent limits at which FDA will regard the food product “adulterated;” and subject to enforcement action under Section 402(a)(3) of the Food, Drug, and Cosmetics Act.

As technology improves, the FDA may review and change defect action levels on this list. Also, products may be added to the list. The FDA publishes these revisions as Notices in the Federal Register. It is the responsibility of the user of this booklet to stay current with any changes to this list.

FDA clearly states that it is economically impractical to grow, harvest and process certain products that are free from such defects. What I find amusing is that every year or so on what seems to be a slow news day, one of the local television stations will hit us with a statement such as “FDA Allows Rodent Hairs in Food X.” They never seem to bother to look at the DALs and why these were established, but the story is presented as if there were an on-line step where someone is dutifully dropping in rodent hairs, insect parts or some other defects that FDA has identified as being “unavoidable” in certain products. On the other hand, there are foreign materials that are simply deemed to be adulterants (see “FDA: Foods – Adulteration Involving Hard or Sharp Foreign Objects”), so as an industry, we must develop, document and implement programs to keep these materials out of what is being processed. Materials such as glass, metal, wood, plastic, bone, rocks and others are among those that the industry works very hard to keep out of raw materials, ingredients and finished goods.

Controlling Foreign Materials in Production
Unfortunately, problems with foreign materials crop up regularly. For those readers who routinely receive recall notices from FDA, the U.S. Department of Agriculture and/or the Canadian Food Inspection Agency, you will see that foreign materials do end up in foods. Kraft Foods issued a massive recall notice for macaroni and cheese in 2015.[2] The company recalled 242,000 cases of product for possible metal contamination and received a total of eight consumer complaints with no reported injuries.

In an effort to control foreign materials, food processors utilize a variety of different programs, many starting with their suppliers. Companies that buy products like preservatives, sugars and other free-flowing materials often mandate that the ingredients be packaged in cases with bright blue or green plastic liners. The theory being that if the bag tears or rips, the blue or green plastic pieces will be more visible and removed from the product being manufactured.

In addition, most suppliers do one or more interventions to ensure that the materials they produce are free from foreign materials. Materials are sieved or screened prior to packaging or passed through a metal detector. Today, specification sheets reflect these practices and the company commitment to quality and safety.


FDA: Foods – Adulteration Involving Hard or Sharp Foreign Objects

Hard or sharp foreign objects in food may cause traumatic injury including laceration and perforation of tissues of the mouth, tongue, throat, stomach and intestine, as well as damage to the teeth and gums. From 1972 through 1997, the FDA Health Hazard Evaluation Board evaluated approximately 190 cases of hard or sharp foreign objects in food. These included cases of both injury and noninjury reported to FDA. The board found that foreign objects that are less than 7 mm, maximum dimension, rarely cause trauma or serious injury except in special risk groups such as infants, surgery patients and the elderly. The scientific and clinical literature supports this conclusion.

Hard or sharp natural components of a food (e.g., bones in seafood, shells in nut products) are unlikely to cause injury because of awareness on the part of the consumer that the component is a natural and intrinsic component of a particular product. The exception occurs when the food’s label represents that the hard or sharp component has been removed from the food, for example, pitted olives. The presence of the naturally occurring hard or sharp object in those situations (e.g., pit fragments in pitted olives) is unexpected and may cause injury. FDA has established DALs for many of these types of unavoidable defects in other Compliance Policy Guides, and, therefore, they are not subject to the guidance in this document.

Regulatory Action Guidance:
The following represent the criteria for direct reference seizure to the Division of Compliance Management and Operations (HFC-210) and direct reference import detention to the Districts:    

a. The product contains a hard or sharp foreign object that measures 7 mm to 25 mm in length, AND

b. The product is ready-to-eat or, according to instructions or other guidance or requirements, it requires only minimal preparation steps, for example, heating, that would not eliminate, invalidate or neutralize the hazard prior to consumption.

Samples found to contain foreign objects that meet criteria a and b above should be considered adulterated within the meaning of 21 U.S.C. 342(a)(1).

The following represent the criteria for recommending legal action to CFSAN [Center for Food Safety and Applied Nutrition] Office of Compliance, Division of Enforcement (HFS-605):

c. The product contains a hard or sharp foreign object that measures 7 mm to 25 mm in length, and the product requires additional preparation or processing that may have an effect on the presence of the foreign objects in the finished food. For example, additional sifting of a product may or may not remove foreign objects, depending on the measurements of the objects and the mesh aperture of the sifter. In these situations, the preparation or processing of the food must be described in the recommendation submitted by the District, OR

d. The product contains a hard or sharp foreign object less than 7 mm in length and, if a special-risk group, as defined in the background section, is among the intended consumers of the product, OR

e. The product contains a hard or sharp foreign object over 25 mm in length.

A sample found to contain a foreign object that meets criterion c, d or e above should be considered adulterated within the meaning of 21 U.S.C. 342(a)(1) if a health hazard is established by CFSAN review. The CFSAN health hazard review in this case will consider various factors including the intended use of the product, subsequent processing steps, official guidance and requirements concerning unavoidable natural defects and other mitigating factors that could eliminate, invalidate or neutralize the hazard prior to consumption of the food product.

If the CFSAN review finds no health hazard associated with a sample containing a hard or sharp foreign object that meets criterion c or d above, the sample should be considered adulterated within the meaning of 21 U.S.C. 342(a)(3) if the CFSAN review finds the article unfit for food. The CFSAN review in this case will consider various factors including subsequent processing steps, extent of contamination and intended use of the product.

CPG 515.350 addresses imbedded objects in confectionary, which may cause such foods to be adulterated within the meaning of 21 U.S.C. 342(d)(1).

Utilizing Those GMPs
The development, documentation and implementation of Good Manufacturing Practices (GMPs) also helps minimize the potential for foreign material issues. For example, the industry has been phasing out the use of wood in food processing operations. Wooden pallets have been replaced with plastic, and many operations that still utilize wood pallets have adopted rigorous pallet management programs to ensure that only good-quality pallets are employed in their facility. Another area where the industry has moved forward with the help of their suppliers has been in managing lubricant use in the plant. Now, some would deem management of lubricants and potential contamination a chemical control program, and they would be correct. However, contamination of foods with any lubricant would render that food adulterated with a foreign material. This applies to food-grade lubricants also. They are allowed “incidental contact” with foods, but they should not end up in a product. Suppliers have responded to industry demands to better control food-grade and non-food-grade lubricants by modifying packaging so that the different types of lubricants may be more easily differentiated. The adoption of more prominent labels and color-coding on lubricants has been a boon to the industry.

Other GMPs in common use across the industry include glass and brittle plastic programs, preventive maintenance, pest management, building management, maintenance and management of utensils and personal hygiene. Ten years ago, blue metal-detectable bandages were a rare sight in food plants. Today, they are part of most plant operations. Of course, what this change has created is more than simply a substitution of bandage types. Each and every time a food processor receives a shipment of blue metal-detectable bandages, they must open the shipment and remove a few of the bandages to run them through the metal detector to verify that they are indeed metal detectable. Of course, this means the procedure must be developed, documented and implemented, which includes maintaining records that the bandages were not only passed through the metal detector but also that they were actually rejected.  

And one of the oldest and best GMPs is still used by many: inspection of the lines. There are many operations that conduct detailed line inspections after cleanup to ensure that the processing lines are intact and undamaged. A small operation that is grinding or chopping a product might not have a metal detector, but that business should know that its chopping operation could pose a contamination risk if it got out of alignment. A postcleanup inspection might reveal scoring within the system, which would pose the question “Where did those metal fragments go?” One of the companies with which I worked had a policy in which a detailed inspection was done on-line up to the fillers. They occasionally discovered that gaskets had broken and vanished, which meant that day’s run was suspect. They continued their daily inspections but adopted a more rigorous program to change out gaskets before breakage occurred. In addition, they changed gasket colors to make them easier to find in product. Their products were soy-sauce based and they originally used dark-gray or black gaskets. Switching to white gaskets made them easier to find.

Foreign Material Interventions
The industry relies heavily on different interventions to minimize foreign material issues. These are used in all kinds of operations, especially those receiving and processing raw agricultural commodities. Operations that receive raw agricultural products, especially those that are mechanically harvested such as spinach, green beans and tomatoes, find all kinds of “surprises” in their incoming materials. The mechanical harvesters scoop up all kinds of things including snakes, birds, mice, rocks, glass and lighter materials such as grass or chaff. And of course, insects and produce that may be slightly moldy will also be included in the harvest. Even hand-harvested products such as leafy greens may have issues, however. Insects and other creatures such as snails and slugs literally glue themselves to the undersides of the leaves and occasionally pass through the whole processing, handling, washing and packaging process.

When people think of foreign material removal, the first operations that come to mind are metal detectors, X-ray machines, magnets and electronic sorters. There are other tools to remove foreign materials, including air blowers, flumes, sizers, reels, and screens, sieves and filters. The type of intervention employed depends on the product and type of foreign material the processor wishes to remove. For example, if a raw agricultural commodity is loaded with chaff or other light materials, air blowers might be utilized. The tomato processing industry makes extensive use of flumes. Fluming washes the tomatoes but also removes rocks and stones, plus some defective fruit.

And of course, there is the old standby: hand sorting. This has advantages and disadvantages. Personally, I believe that the disadvantages outweigh the advantages. Workers assigned to sorting lines get tired, they can miss things and there is a higher potential for suffering repetitive-motion injuries. To minimize the latter point, processors have been known to stop the lines for a few minutes each hour to allow their workers to rotate positions and go through a series of exercises to minimize the potential for injury. It is also a good idea to rotate people on and off the sorting line to keep them fresh and sharp. Some plants rotate people at intervals of every hour or less, realizing that the efficiency of the people doing the sorting drops over time. Persons doing the sorting also must be trained on what might come down the line and understand that it is their job to remove it. Quality managers have told me that they have seen sorters refuse to remove certain materials, such as mice, from the line, with the result that the rodent ended up going into the finisher.

Other interventions include the following:

Magnets: Magnets will remove ferrous and nonferrous metals. They can also be used to protect processing equipment downstream of where the magnets are located. This is why they are often used in juice and beverage processing operations. The magnets will attract the piece of metal, preventing it from potentially damaging a filler and causing costly repairs and downtime. And magnets can enhance product quality. The advantage of magnets is that they will remove very, very small pieces of metal, such as rust particles, whereas metal detectors and X-ray machines have a finite detectability. Two kinds of magnets are used in food processing: ferrous magnets and rare-earth magnets. Rare-earth magnets are the stronger and more effective of the two types of magnets. They can remove fine metal dust and work-hardened or braided stainless steel.

There is also a range of formats that allows magnets to be used in different processing systems. These include grate, tube, plate, liquid line, pneumatic, chute, pipe and drum magnets. Each of these different magnets has different applications and different product uses. Processors who do dry blending often install grate magnets where bags are dumped to remove metals at the start of the process. Processors of dried fruit install plate magnets immediately before filling to remove metal dust, specifically rust.

Magnets must be inspected and tested on a regular schedule. If they are used as a Critical Control Point (CCP), they should also be validated. Most processors will mandate that in-line magnets be inspected and cleaned at least once a day. As part of this process, they often have the people performing these activities collect what is on the magnet and save it for future evaluation by the quality staff.

Magnets should also be tested on a regular schedule to ensure that they are performing properly. How often this is done depends upon individual companies. Equipment manufacturers recommend that this be done at least once a year, but companies should conduct a risk assessment to establish a schedule for their own operations. Pull testing repeatedly measures the holding strength in ounces of force or pounds at a predetermined distance from the surface or on the surface of the magnet itself. This may be done by the equipment manufacturer or in-house. It is not a hard test to learn how to do. Finally, magnets should be validated to ensure that they remove the metals being targeted. I have seen processors do this by passing product spiked with a known number of metal pieces. They would then look at the magnet to verify that the metal was on the magnet.

Metal Detectors: Metal detectors are designed to detect all metal in food products above a certain size. The size of metal that is detectable depends upon the product and the package it is in. There are different types of metal detectors available to the food industry, including systems that pass the products through on a conveyor, in-line systems for liquids and vertical inspection systems. Metal detectors are almost always designed to reject product found to contain metal, although there are occasional units in which the product conveyor simply stops. Ideally, the best location for a metal detector is after packaging, which is why conveyor systems are so popular. If metal is detected, the package will be rejected. Of course, if the package itself contains metal (common with packages made from recycled materials), the processor might want to consider adding another metal detector to scan the packages themselves prior to adding the food product. This is, however, an expensive option.

Processors should work with the equipment manufacturer to establish minimum detection limits for the standards used with the unit. A processor might demand that their suppliers pass all products through a metal detector that can detect the following standards: 1.0 mm ferrous, 1.5 mm nonferrous and 2.0 mm stainless steel. If the processor is manufacturing hot dogs in a vacuum package, the customer demands can probably be met. However, if the goal is to pass 20-pound boxes of frozen entrees through the unit, that detection limit will probably be impossible. Processors should obtain a letter from their equipment manufacturer defining the minimum detection limits for the unit. Based on this letter, the processor should obtain the necessary standards from the equipment manufacturer, that is, a ferrous, nonferrous and stainless steel standard. For stainless steel standards, make sure that the type of stainless in the standard reflects the primary type of stainless in your plant and equipment. Processors must also decide, based on risk, how often they should test their metal detectors using these standards. At a minimum, each standard should be tested at the start and end of a product run with one test during the middle of the run. In reality, most operations will conduct these tests more frequently. Many operators write their procedures so that testing is at the minimum level noted above, but in actual operations will test every 1 to 2 hours. Why? Because no auditor will downgrade an operation for exceeding testing levels.

There is an ongoing debate as to how a company’s metal detector should be incorporated into the organization’s food quality and safety programs. Some companies have determined that metal detection should be a CCP in their Hazard Analysis and Critical Control Points (HACCP) plan, whereas others deem it part of quality management (prerequisite program). If the manufactured products are chopped or ground, and the company’s Hazard Analysis determines that there is a significant potential for metal contamination, the company will probably adopt the former. However, if a processor is producing purées or juices, it might install an in-line metal detection unit not only to look for metal but also to protect equipment that is located downstream of the unit. Of course, there are processors that base this decision not on risk but on customer demands. If a processor’s primary customer demands that metal detection be a CCP, they will usually comply.[3]

X-Ray Machines: As noted earlier, there is a push within the industry to have their suppliers move from metal detectors to X-ray machines. X-ray technology has improved immeasurably in the last few years. Systems are faster, more versatile and can detect more than just metal. The same principles that were mentioned for metal detectors apply for X-ray systems. Work with the equipment manufacturer to determine optimum detectability and selection of standards; conduct tests to validate the system, especially if the X-ray system will be deemed a CCP; and examine what is rejected by the machine. And finally, work with the supplier to set up the machine for each product that will be run on the line.

X-ray machines can detect metal, glass, stones, calcified bone and some plastics. Depending upon the product and the material, they may be able to detect other materials. Note that one of the materials that X-ray machines can detect is calcified bone. Utilizing an X-ray system on chicken may not be as effective as one would think, because many birds are slaughtered before their bones have fully calcified.[4]

Programs for Minimizing Defects
Many of the programs highlighted above may be used to minimize the defects defined in the DAL handbook. Among these defects are the following:

•    Contamination

•    Copepods

•    Damage

•    Decomposition

•    Decomposition Byproducts

•    Infestation/Insect Fragments

•    Mammalian Excreta

•    Mold

•    Rot

•    Rodent Hairs

Pest management and cleaning and sanitizing may be the most important of the GMPs when it comes to minimizing potential problems. Remember, FDA has set these limits because they are deemed unavoidable, but that does not mean having them in foods is a good idea. In fact, finding such defects in foods, whether they exceed established limits or not, could be an indication that a processor’s GMP programs are not as good as they should be.

Of course, whenever FDA establishes a limit for something, there must be a method to evaluate that limit. Most of the defects defined in the DAL handbook have established AOAC (Association of Official Analytical Chemists) methods or FDA’s Macroanalytical Procedures Manual (MPM).[5] The former must be purchased from AOAC, whereas the latter is available on FDA’s website.

Many of these methods are old and require equipment that some would deem outdated, but they are part of the regulatory framework, so processors must be aware of the DALs and how to evaluate their products. For example, the DALs for wheat flour, tomato paste or purée and paprika are listed below.1 These examples show what is expected in two very common ingredients and in a spice used throughout the food industry. The DALs for related products will be very similar. The DAL defines the type of defect, the limits, the test method, the source or sources and the significance of the defect.

Wheat Flour
•    Insect filth (AOAC 972.32): Average of 75 or more insect fragments per 50 grams

•    Rodent filth (AOAC 972.32): Average of one or more rodent hairs per 50 grams

•    Defect Source:
        Insect filth: Pre- and/or postharvest and/or processing insect infestation
        Rodent hair: Postharvest and/or processing contamination with animal hair or excreta

•    Significance: Aesthetic

Tomato Paste or Purée
•    Mold (AOAC 965.41): Average mold count in six subsamples is 45 percent or more, and the mold counts of all of the subsamples are more than 40 percent

•    Defect Source: Pre- and/or postharvest and/or processing infection

•    Significance: Aesthetic   

Ground Paprika
•    Mold (AOAC 945.94): Average mold count is more than 20 percent

•    Insect filth (AOAC 977.25B): Average of more than 75 insect fragments per 25 grams

•    Rodent filth (AOAC 977.25B): Average of more than 11 rodent hairs per 25 grams

•    Defect Source:
        Mold: Pre- and/or postharvest mold infection
        Insect filth: Pre- and/or postharvest and/or processing insect infestation
        Rodent filth: Pre- and/or postharvest and/or processing contamination with animal hair or excreta

•    Significance: Aesthetic, potential health hazard; mold may contain mycotoxin-producing fungi  

The methods used for testing food for defects are not ones that a person would normally learn in school. In fact, they are not tests that are done in many food laboratories. Nina Parkinson, director of the University of California Davis Laboratory for Research in Food Development, runs yearly schools to teach some of the procedures used for testing defects in foods. Among the tests she teaches are those for insect fragments and mold counting, since these are important for tomato processing and its products. She acknowledges that some of the equipment needed for the tests is painfully out of date, but the industry needs to understand how to do these tests.  

It would be a good idea for all food processors to download a copy of FDA’s MPM[5] from the agency’s website and determine whether your company should embark on a macroanalytical testing program. There may not be DALs established for each and every product that may be produced, but development of such programs could enhance overall food quality and your standing with consumers. In addition, under the Federal Food, Drug, and Cosmetic Act, a food may be deemed to be adulterated “if it consists in part or whole of any filthy, putrid or decomposed substances, if it is otherwise unfit for food.” Mold or insect fragments in products could render the item in question adulterated, and it is against the law to distribute items that are adulterated. The MPM lists methods for testing the following categories of foods:

•    Beverages and Beverage Materials

•    Bakery Products, Cereals and Alimentary Pastes

•    Grains and Grain Products

•    Chocolate, Sugars and Related Products

•    Miscellaneous and Multiple Food Products

•    Dairy, Cheese and Related Products

•    Seafood

•    Spices, Condiments, Flavors and Crude Drugs

•    Fruits and Fruit Products

•    Nuts and Nut Products

•    Vegetables and Vegetable Products

•    Cosmetic Products

Within each category of food, different products are listed. As an example, one can find potato chips listed under Vegetables and Vegetable Products.

Building a Macroanalytical Laboratory
For a company that elects to do macroanalytical work in-house, it will be much less expensive than it would be to put in a chemistry or microbiology laboratory. Unless an operation elects to do specialized analyses, the most expensive pieces of equipment required would be microscopes. The macroanalytical laboratory should have at least two scopes: a stereomicroscope and a compound microscope. The minimum specifications for the stereomicroscope would be an inclined binocular body, with adjustable interpupillary distance, over sliding or revolving parfocal, achromatic objectives, with a geared prism housing, mounted on a base and capable of illumination by transmitted or reflected light. The microscope should be flexible for adaptation to other applications and stable for possible photomicrography. A protective cover is required. Eyepiece micrometer and hand rests are recommended.[5] The basic equipment required to do such work is outlined in the MPM.

Training your people to do the work is another matter. When reading over the methods for doing this work in the MPM or the AOAC procedures, they may appear simple, but they are not. They require practice, practice and more practice. Nina Parkinson will tell you that a significant part of the classes that she teaches is devoted to just this: practice.

Foreign materials of any kind in foods are not desirable. They can render a food unsafe, adulterated or simply undesirable. There are probably many who have found an insect or hair in their food, and it is not appetizing. Remember the old joke: “What is worse than finding a worm in your apple?” Answer: half a worm. Food processors must be proactive in their work to minimize foreign materials in foods. This is a program that depends on suppliers, in-house GMPs, prerequisite programs for HACCP and the Food Safety Management System, quality and safety systems and properly maintaining these programs. Macroanalytical testing can further augment what is done to control foreign materials such as metal, glass and other materials. And remember, a food product or ingredient may be deemed safe, but it can still be adulterated. Look at the Kraft example cited earlier in the article. There were no reported injuries, but consumers detected metal and Kraft initiated a massive recall.   

Richard F. Stier is a consulting food scientist and a member of the Editorial Advisory Board of Food Safety Magazine. He can be reached at [email protected].

3. Stier, RF. 2013. “Metal Detection: Quality or Safety.” Food Engin April:29–31.
4. Stier, RF. 2014. “Foreign Material Control: Food Quality, Safety or Both.” Food Safety Magazine 20(2):36–45.


Categories: Contamination Control: Physical, Reduction Methods; Facilities: GMPs; Testing and Analysis: Methods, Physical