Posted On: June 10, 2021

What Are The Four Types of Food Contamination?

When food becomes contaminated with something that shouldn't be there, it can be dangerous to your customers and disastrous for your business.

That's why preventing food contamination is such an important component of food safety. Before you can prevent it, you have to understand what kinds of things can contaminate food and the mechanisms that can lead to contamination.

Types of Food Contamination

Traditionally, we taught that there were three types of food contamination: physical, chemical, and microbial (sometimes called biological). These days, we add a fourth type: allergenic.

All food is at risk from these four types of contamination. Consumption of contaminated food can result in sickness or death, so it's important to understand how to prevent foodborne illness by safeguarding against all types of contamination.

What is Cross-Contamination?

There are many ways for contaminants to enter food – during cultivation, processing, or in the kitchen.

Contaminants aren't always introduced to food directly. Cross-contamination is the accidental transfer of contaminants into the food from a surface, object, or person. Four common sources of cross-contamination include clothing, utensils, food handlers, and pests.

People usually mean biological or allergenic contaminants when they talk about cross-contamination, but it can involve any of the four contaminants.


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What is Physical Contamination?

Physical contamination refers to foreign objects that contaminate food. It can happen at any time between farm and table.

Physical contaminants can cause choking, cutting, or broken teeth, but they can also introduce harmful microorganisms that come with their own hazards. Even if a customer isn't ill or injured, finding something in their food can be very distressing.

Examples of Physical Contamination

Common examples of physical contaminants include hair, bandages, fingernails, jewelry, broken glass, metal, paint flakes, bone, the body parts of pests, or pest droppings.

Preventing Physical Contamination

Sourcing food from reputable suppliers is an important start, but employees need to take measures to make sure physical contaminants aren't introduced in-house.

Common policies include:

  • Tying hair back or wearing a hair net – don't forget about beards!
  • Remove jewelry for work hours. Jewelry can also be a source of microbial contamination.
  • Wear gloves over any hand bandages and/or use brightly colored bandages that are easier to spot if they fall off.
  • Implement and maintain a strict pest control system.
  • Take damaged equipment, dishware, or glassware out of commission immediately and repair as soon as possible.

What is Chemical Contamination?

Chemical contamination happens when food comes into contact with toxic chemicals. Any chemical that can make you sick if you ingest it directly can also cause a problem if it contaminates your food

This can happen before the food arrives at your restaurant, or it can happen on-premises. Chemical contaminants can be artificial or natural, from the food itself.

Examples of Chemical Contamination

Common examples of artificial chemical contaminants include detergent, sanitizer, other cleaning products, fertilizers, herbicides, and pesticides.

Examples of natural chemical contaminants include the glycoalkaloids produced by potatoes and stored under the peel and in the eyes or sprouts. Fugu sushi poisoning is a more exotic example – if pufferfish is prepared incorrectly, it may include tetrodotoxin.

Preventing Chemical Contamination

Again, using food suppliers that take their own precautions is important.

Common policies to prevent in-house chemical contamination include:

  • Store chemicals separately from food.
  • Follow chemical manufacturers' instructions for application, dilution, contact time, and water temperature.
  • Make sure employees understand the appropriate amount of product to prevent residue.
  • Use pest control products carefully or use a professional pest control service.
  • Cover food during cleaning and pest treatment.
  • Rinse surfaces, glassware, dishes, and cutlery properly after sanitization.
  • Wash fruits and vegetables to remove pesticides, fertilizer, and other residues.
  • Use only food-grade plastics and metals in a kitchen.

What is Biological Contamination?

Biological and microbial contamination are sometimes used interchangeably, but biological contamination is technically a broader umbrella.

Microbial contamination covers microorganisms like bacteria, viruses, parasites, protozoa, fungi (including mold), and prions. It can also include the toxins these microorganisms produce. Biological contaminants include all that but also any biological matter produced by humans, rodents, or insects.

Microbial contamination is the most common cause of foodborne illness, sometimes called food poisoning. It's also a common source of food spoilage.

Examples of Microbial Contamination

The most common microbial contaminants are norovirus, Listeria, Salmonella, E. coli, and Campylobacter.

There are also toxins from animals like fish and shellfish or microbes like Salmonella, Staphylococcus, and Listeria. Many toxins are more heat-resistant than the bacteria that make them, so they require more stringent precautions to keep them from building in the first place.

Some foods are more likely to harbor dangerous levels of microbes or microbial toxins than others. Foods that are moist, neutral in acidity, and/or high in protein or starch tend to grow microbes the best – they're known as Time and Temperature Control for Safety (TCS) foods because they require specific precautions related to those factors.

Preventing Biological Contamination

Using reputable suppliers, inspecting each delivery, and refusing suspicious items can be critical to avoiding microbial contamination of the food you serve. That includes rejecting things like:

  • Dented, rusted, or swollen cans and jars with bulging lids
  • Food that arrives at an improper temperature
  • Frozen foods that show signs of thawing
  • Meat that has a suspicious color, texture, or odor
  • Baked goods or dairy products with signs of mold

You can minimize the risk of in-house biological contamination if you:

  • Send employees home when they show symptoms consistent with foodborne illness.
  • Follow TCS precautions with high-risk food at all times, from receiving to serving.
  • Keep raw and ready-to-eat food separate at every stage.
  • Store food to prevent cross-contamination.
  • Wash raw fruit and vegetables properly (but don't wash meat).
  • Implement proper cleaning and sanitation procedures, as well as a pest control system.
  • Teach employees proper hygiene protocols and food handling techniques that prevent cross-contamination.

What is Allergenic Contamination?

Allergenic contamination happens when food that causes an allergic reaction comes into contact with another food.

For the wrong customer, an allergic or otherwise adverse reaction to food can result in anything from hives to gastrointestinal distress to potentially deadly anaphylaxis.

Examples of Allergens

People can develop allergies to many different types of food, but the most common examples of food allergens include:

  • Eggs
  • Milk
  • Soy and soybeans
  • Peanuts
  • Tree nuts (like almonds, walnuts, or pecans)
  • Wheat, rye, barley, and oats
  • Fish
  • Crustacean shellfish (like crab, lobster, or shrimp)

Lesser-known but documented food allergies include celery, mollusks, mustard and mustard-containing sauces, sesame seed, lupin flour, and sulfite/sulfur dioxide (a preservative).

Preventing Allergenic Contamination

If you're going to advertise allergen- or gluten-free food, you need to really commit.

Policies to prevent allergenic contamination include:

  • Ensure your whole supply chain takes allergenic contamination seriously.
  • Store allergenic food separately.
  • Separate the prep areas, equipment, utensils, and other items for individual allergens from one another and from non-allergenic food.
  • Label and store equipment and utensils to prevent cross-contamination.
  • Use adequate cleaning and disinfectant procedures for everything that touches non-allergenic food.
  • Put the precautions you do (and don't) take on your menu so that customers can decide for themselves based on their individual circumstances

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