Unit 1 – Food Safety

1.3 Safety of Our Foods

What Is a Safe Food Supply?

Image of father and daughter grilling outdoors.
Image: USDA SNAP Ed Public Domain

A safe food supply is free of physical, chemical, and biological contaminants. Physical contaminants include substances that accidentally get into food during any stage of the food chain such as hair, glass, jewelry, plastic, bones, bugs, or stones. Some cause immediate problems such as choking, a broken tooth, or cuts to the lining of the digestive tract. Chemical contaminants include fertilizers or pesticides used in farming or kitchen cleaning products used during meal preparation. It may take years for health problems caused by a chemical to show symptoms. Section 1.8 discusses more various chemical contaminants.

Biological contaminants are microorganisms such as bacteria, viruses, mold, fungi, and the toxins these microbes produce. (These microbes are often called germs.) This type of contamination typically occurs during processing, preparing, or serving foods and is the main focus of this unit. Problems resulting from biological contamination are often called “food poisoning.” The illnesses they cause generally occur within a day or two after eating the contaminated food. Some people call it the “stomach flu” because of stomach aches, nausea, vomiting, and diarrhea.

In general, our food supply is much safer than it was 100 years ago. However, outbreaks of food poisoning do occur, such as the recent ones at Chipotle Mexican Grill. Close to 1,100 people became ill after eating at a Chipotle restaurant. An FDA report describes the cause of the outbreak:

From approximately 2015 to 2018, Chipotle faced at least five food safety incidents at various restaurants around the country, which stemmed primarily from store-level employees’ failure to follow Chipotle’s food safety policies and procedures, including the policy requiring the exclusion of restaurant employees who were sick or recently had been sick, as well as a failure by restaurant employees to hold food at appropriate temperatures to prevent and control for the growth of foodborne pathogens. [1]

The culprits were E. Coli  in the 2015 outbreaks and Clostridium perfringen in 2018. (We will discuss these bacteria in 1.8 Microbes that Contaminate Foods. ) Both bacteria are easily transferred to food from sick food-handlers; these bacteria proliferate when foods are held at room temperature. In 2020, Chipotle agreed to pay a $25 million fine to resolve charges stemming from the outbreaks. The fine inspired the restaurant chain to improve their employee food safety training program.

Although the Chipotle incident and illnesses that resulted put doubt in many people’s faith in restaurants, the number of people affected is just a fraction of the 48 million foodborne illnesses that occur each year.

The Government’s Role in the Food Supply

Thanks to the government, our food supply is closely monitored. Foods and beverages served in school cafeterias and restaurants or purchased in grocery stores are tightly regulated. Food processing plants often have onsite inspectors ensuring that safe food handling practices comply with guidelines. Food processing plants often have onsite inspectors ensuring that safe food handling practices comply with state and federal guidelines. If you have worked in a restaurant, you might remember the health department inspector’s surprise visits to check the temperatures of foods and make sure all refrigerators and freezers had thermometers. The next time you are in a restaurant, look for the inspection form with a numeric score. You can see Tennessee restaurant inspections online.

Internationally, the Food and Agriculture Organization (FAO) of the United Nations has similar global programs to promote food safety worldwide. They describe the process as:

Keeping food safe is a complex process that starts on the farm and ends with the consumer. FAO is the only international organization overseeing all aspects of the food chain, thereby providing a unique, 360° vision on food safety. A longstanding partnership with the World Health Organization (WHO) enhances this perspective.

Through complementary mandates, FAO and WHO cover a range of issues to support global food safety and protect consumers’ health. WHO typically oversees and maintains strong relationships with the public health sector, and FAO generally addresses food safety issues along the food production chain.[2]

If governments monitor our global food supply so closely, why do an estimated that 600 million – almost 1 in 10 people in the world — fall ill after eating contaminated food? And 420,000 die every year, with children under the age of 5 years at exceptionally high risk. African and South-East Asia Regions have the highest burden of foodborne diseases.[3]

Before reading further, watch the short FAO video that describes how food safety is a shared responsibility.

VIDEO: “Food Safety Is Everyone’s Responsibility,”  By The Food and Agriculture Organization of the United Nations. June 2021, (1 minute)


Although some foods can become contanminated during food processing,  the problem generally results from improper food handling at home.   Foods may become contaminated with certain disease-causing microbes, also known as pathogens.  Foodborne illnessessometimes called  food poisoning,  may cause nausea, vomiting, stomach cramps, and diarrhea. Symptoms can be severe, and some foodborne illnesses can even result in death.

What Are the Types of Foodborne Diseases?

According to the CDC, food scientists have identified more than 250 different foodborne diseases. They may be either infectious or toxic in nature. Most are food infections caused by eating food contaminated with live microorganisms, such as bacteria, parasites, or viruses. The infection then grows inside your body and makes you sick. Food infections can be sporadic, and most of us do not report them to health professionals. However, occasional outbreaks occur that put communities, regions, or even entire nations at risk. For example, in 1994, an outbreak of salmonellosis infection occurred in the United States due to contaminated ice cream. An estimated 224,000 people became ill. In 1988, contaminated clams resulted in an outbreak of hepatitis A in China, which affected about 300,000 people.[5]

Live microorganisms are not the only culprits in food poisoning. These microbes can produce toxins that cause foodborne illnesses just like live bacteria, viruses, and molds do. Cooking does not destroy the toxins.

One of the biggest misconceptions about foodborne illness is that the last meal you ate triggers the disease. However, it may take several days before the onset of symptoms. If you develop a foodborne illness, you should rest and drink plenty of fluids. Avoid antidiarrheal medications because they could slow your body’s ability to eliminate the contaminant.

How Do  Microorganisms Reproduce?

Bacteria, one of the most common causes of food infection and toxin production, are single-celled microbes that are too small to be seen with the human eye. They reproduce by one bacterium dividing into two, a process known as binary fission.  Like all living things, bacteria depend on certain conditions to survive and thrive. For them to reproduce at a level that will cause illness, these six conditions are involved: 1) food, 2) acid, 3) temperature, 4) time, 5) oxygen, and 6) moisture, or “FAT TOM” for short.

Each of these six factors contributes to bacterial growth in the following ways:

  • Food: Bacteria require food to survive. For this reason, moist, protein-rich foods are good potential sources of bacterial growth.
  • Acid: Bacteria do not grow in acidic environments. Therefore, lemon juice and vinegar serve as preservatives.
  • Temperature: Most bacteria will proliferate between 40°F and 140°F (4°C and 60°C). USDA considers this to be the danger zone for microbial growth. (ServSafe® uses 41°F to 135°F as the danger zone for commercial foodservice.)  Cold temperatures do not kill the bacteria; they only prevent their reproduction. The optimal temperature required to destroy different types of bacteria varies, but temperatures above 165°F destroy most. Therefore, you should use a thermometer to check the internal temperature of foods.
  • Time: Bacteria require time to multiply. When small numbers of bacteria are present, the risk is usually low. Still, extended time with the right conditions will allow the bacteria to multiply and increase the risk of illness.  
  • Oxygen: Most bacteria are aerobic and require oxygen to grow. They will not multiply in an oxygen-free environment such as a vacuum-packaged container. A few bacteria are anaerobic and will only grow in oxygen-free environments.  Clostridium botulinum is anaerobic and causes the deadly botulism.
  • Moisture: Bacteria need water to survive and proliferate in moist foods. Dry and salted foods have a lower risk of being a safety hazard. High amounts of sugar also decrease the moisture available for bacteria.

What Foods are  Potentially Hazardous?

Foods that have one or more of the “FAT  TOM” conditions described above are considered potentially hazardous foods (PHFs).  These foods are perishable and will spoil or “go bad” if left at room temperature too long.

Generally, a food is a PHF if it is:

  • Of animal origin such as meat, milk, eggs, fish, shellfish, poultry (or if it contains any of these products)
  • Of plant origin (vegetables, beans, fruit, etc.) that has been cooked
  • Any of the raw sprouts (bean, alfalfa, radish, etc.)
  • Any cooked starch (rice, pasta, etc.)
  • Any type of soya protein (soya milk, tofu, etc.)

Look over Table 1.1  to see which foods fit into the  PHF category and those in the  non-PHF group.

Table 1.1   Potentially Hazardous Foods Vs Non-Potentially Hazardous Foods

Potentially Hazardous Foods Non-Potentially Hazardous Foods
Raw or cooked beef, chicken, or any meat Beef jerky
Tofu Dried soy beans
Opened cans of vegetables, soup, or meat Unopened cans of vegetables, soup, or meat
Scrambled eggs Uncooked egg in the shell
Cooked rice or pasta Uncooked rice or pasta
A cream filled donut A plain bagel

One of the most important factors to consider when handling food properly is temperature. Table 1 .2 lists important temperatures to remember related to foods.   One key tip to remember is to “keep hot foods hot and cold foods cold” because microbes do not reproduce in hot or cold foods.

Table 1.2   Important temperatures to remember

Celsius Fahrenheit What happens?
100° 212° Water boils
74° 165° Most pathogens die, although “thermophiles” may survive much higher temps
60° 140° Pathogens do no reproduce.  Keep hot foods above this temperature.
Temperature ranges that bacteria thrive. The Danger Zone” is from 40° to 140° Fahrenheit (4° to 60° Celsius) 
20° 68° Food must be cooled from 60°C to 20°C (140°F to 68°F) within two hours or less
40° Food must be cooled from 20°C to 4°C (68°F to 40°F) within four hours or less
32° Water freezes
–18° Frozen food must be stored at −18°C (0°F) or below


Review Questions


  1. US Food and Drug Administration. “Chipotle Mexican Grill Agrees to Pay $25 Million Fine to Resolve Charges Stemming from More Than 1,100 Cases of Foodborne Illness.” April 21, 2020. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/press-releases/chipotle-mexican-grill-agrees-pay-25-million-fine-resolve-charges-stemming-more-1100-cases-foodborne
  2. FAO. Food Safety and Quality. Retrieved from http://www.fao.org/food-safety/en/ June 26, 2021
  3. WHO. Food Safety. Retrieved from https://www.who.int/news-room/fact-sheets/detail/food-safety


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Introduction to Nutrition and Wellness Copyright © 2022 by Janet Colson; Sandra Poirier; and Yvonne Dadson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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