The most frequently encountered U.S. Food and Drug and Administration (FDA) Food Code violation found by sanitarians during inspections and audits is temperature abuse. This is primarily encountered on the refrigeration side, handwashing notwithstanding. In my recent experiences, I learned that cold holding temperature abuse conditions do not arise so much from operational issues that are easily correctable, such as pre-chilling ingredients before assembling salads or placing hot foods in shallow pans for cooling. Rather, these issues arise from the use of inappropriate refrigeration equipment. For example, it is not unusual for us to find beverage coolers used to maintain the temperature of potentially hazardous foods or display refrigerators used as blast chillers.

While the FDA Food Code details the temperature and the length of time foods can be maintained in refrigeration (as well as out-of-refrigeration), it does not specify the type of refrigerator required to do so. The one time this question is routinely raised is during the plan review process. But conditions and business practices change over time and the refrigeration equipment that was appropriate when the facility was first opened may not be appropriate now.

The application and use of refrigeration equipment has certainly been implicated as a contributing factor in several recent foodborne illness outbreaks with which I have had some involvement as a consultant. It dawned on me that information on refrigeration equipment is not readily available, except through equipment manufacturers and standard-setting organizations such as NSF International. I must admit, as a regulator, my concern is focused on time and temperature compliance and assuring that thermometers are properly placed in each unit; not so much with the type of equipment used. Therefore, I ask you to bear with me while I broach this topic as an introduction to the various types of refrigeration equipment and their proper use in an effort to provide some solutions to cold holding temperature abuses that can be avoided in your operation.

The Low-Down on the Cool-Down
Before mechanical refrigeration systems were invented, people cooled their food in springs or with ice and snow. This was the only means of refrigeration for most of history, and we still use it regularly in display and service. In the past, perishable foods were kept in cool cellars or in buckets lowered into wells. The first cold cellars were holes dug into the ground, lined with wood or straw and packed with snow. A device still used in some areas is a room built with porous walls over which water trickles; as the water evaporates the room is cooled. In visiting historical houses, it’s no small wonder that a spring of cold water often determined its location on the property. A springhouse was usually built over the flowing water that was led through troughs in which crocks of food were placed to keep them cool. In winter, ice was stored in icehouses for use in the summer. Similarly, natural ice from commercial icehouses was used in cities until artificial methods of producing ice were initiated in the middle of the nineteenth century. In fact, growing up in the Big Apple, I remember my folks using an icebox until after WWII when consumer goods again became readily available.

The first known artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in Scotland in 1748. However, he did not use his discovery for any practical purpose. In 1805, American inventor Oliver Evans designed the first refrigeration machine. The first practical unit was built by Jacob Perkins in 1834; it used ether in a vapor compression cycle. An American physician, John Gorrie, built a refrigerator based on Oliver Evans’ design in 1844. His machine was used to make ice to cool the air for his yellow fever patients. The process of liquefying gas, the basis of modern refrigeration technology, was patented by a German engineer, Carl von Linden in 1876.

Modern mechanical refrigeration systems are based on the principle that absorption of heat by a fluid (refrigerant), as it changes from a liquid to a gas, lowers the temperature of the objects around it. In the compression system used in commercial installations, a compressor, controlled by a thermostat, exerts pressure on a vaporized refrigerant, forcing it to pass through a condenser, where it loses heat and liquefies. It then moves through the coils of the refrigeration compartment. There, it vaporizes, drawing heat from whatever is in the compartment. The refrigerant then passes back to the compressor and the cycle is repeated.

As you can see, mechanical refrigeration systems are a relatively new technology in world history. It is not surprising therefore that we often use our modern refrigeration equipment as if we’re were still lowering a bucket into a well or buying a block of ice to keep our milk from spoiling.

Types of Refrigeration Equipment
Food safety strategies require all potentially hazardous foods needing refrigeration to be kept at or below 41F (5C), for a maximum of seven days, except when being prepared or served, or at 45F (7C) or between 41F (5C) and 45F (7C) for a maximum of four days in existing refrigeration equipment that is not capable of maintaining food at 41F (5C).

Having learned this paradigm, I have also learned that not all refrigerators are created equal. Refrigerators are designed and manufactured to meet the needs, operations and conditions in the commercial setting. Each type of refrigerator is designed to meet specific materials and performance requirements that are detailed in ANSI/NSF standards, and, that these standards are consistent with the Food Code. The selection of a refrigerator depends on several factors including the menu (type of food), preparation, volume (number of meals per day) and frequency of delivery. Before selecting refrigeration equipment, consult your local sanitarians or environmental health officers, who can give you helpful advice.

“Refrigerator” is defined as: “Equipment designed to enclose an area of mechanically refrigerated and temperature-controlled air used to maintain prescribed cold food holding temperatures.” There are approximately 19 different types of refrigerators, including their configurations, which fall under this description and are used in the food industry. Many of these types can be grouped into the following categories. (For purposes of this article, I have taken some liberty with the official definitions and refer you to ANSI/NSF 7-2000, Commercial refrigerators and freezers, for more concise wording.)

Beverage Coolers are refrigerators intended solely for the storage and/or display of packaged beverage products that are not potentially hazardous foods, such as carbonated beverages, beer and wine. They are not designed to do anything else.

Display Refrigerators are designed to display foods to the consumer for purchase in areas where the environmental conditions are controlled and maintained. There are several types of display refrigerators; in fact, NSF has definitions (NSF/ANSI 170-2002) for about six different types depending on their use, door configuration and the environmental conditions in which they are installed. This type of refrigerator is designed to maintain safe temperatures and not for cool down.

Rapid Pull-Down Refrigerators, which are also known as Blast Chillers, are specifically designed for rapid intermediate chilling of food products within a specified time period. When used correctly, these are ideal for the rapid cooling of hot foods.

Refrigerated Buffet Units are designed to receive refrigerated food and maintain food product temperatures. They are intended for customer self-service, such as a salad bar.

Refrigerated Food Preparation Units are designed with a refrigerated open top or open condiment rail. These include refrigerated sandwich units and pizza preparation tables for example. These units will maintain cold foods: cold.

Storage Refrigerators are designed for the cold storage of non-frozen foods between periods of preparation, service, display or sale. Probably a better moniker for these units is “day refrigerator” because they are not intended for the long-term storage of foods.

• The Walk-in Refrigerator is an enclosed, mechanically refrigerated and temperature-controlled room with integral walls, floor, and ceiling used to maintain prescribed cold food holding temperatures. I think that we can all agree that this type of refrigerator is probably the most widely used and the least understood, but more on this in a moment.

We do not consider the use of domestic or household refrigerators as appropriate in a commercial food setting. In fact, they are unacceptable because their cooling capacity, temperature recovery, air flow and durability are unknown. There are no performance requirements for domestic refrigeration equipment.

Finally, for all practical purposes, after conducting a pre-inspection menu review I look at each type of refrigeration unit in each establishment as appropriate, to ensure the maintenance of safe temperatures.

Practical Tips
Other than using the proper refrigeration equipment for the type of food, there are some simple and sensible practices that optimize the use of this equipment. Even though it is required by the Food Code, use a fridge thermometer to regularly check the temperature of the refrigeration equipment. The coldest part of the fridge should be between 32F and 41F (0C and 5C). As a rule of thumb, it is a good practice to make sure the refrigerator temperature is 40F or below. Check the temperature at regular intervals throughout the day to spot potential problems with temperature recovery. Use a probe thermometer to check if food being chilled or kept cold before serving is at a safe temperature.

In placing foods in a refrigeration unit, particularly a walk-in refrigerator, remember to keep raw food below ready-to-eat (RTE) food in the fridge. Or use separate fridges for raw and RTE food, if possible. Place any raw food that has the potential of leaking on the lowest shelves.

As another good rule-of-thumb, refrigerate or freeze perishables, prepared foods and leftovers within two hours. Make food cool more quickly by dividing it into smaller amounts and placing it in shallow dishes, or use cooling (ice) sticks to rapidly cool foods in stockpots.

Make a temperature map of the inside of storage and walk-in refrigerators by placing several thermometers throughout the unit and take readings at 10- to 15-minute intervals during periods of temperature recovery. The coldest section of the refrigerator should be used for potentially hazardous foods.

Don’t over-stuff the refrigerator. Cold air must circulate to keep food safe. If you had a recent delivery, make sure that the product is stored properly, below the stack limit line. You can actually map the “sweet spot” for cooling within a walk-in refrigerator by using a smoke tube and finding the area where the air has the greatest turbulence. Leave the spots of least turbulence for produce and other non-potentially hazardous foods.

A regularly performed maintenance program will help ensure that refrigeration equipment not only serves a long and useful life but also operates more efficiently. The following are a few tips:

Ongoing: Move delivered product quickly into the walk-in coolers from the receiving dock. Allowing the product to warm up to outdoor temperatures will increase the pull down load on the refrigeration system.

Monthly: Clean the condenser coils to maintain optimum heat transfer performance. Check to be sure that display case air curtains, grilles, or registers are clean and free of obstructions to assure proper air flow across the evaporator coils. Check door gaskets for leaks and tears to minimize infiltration loads. Check the refrigerant charge; add more when needed. Check the defrost cycle time-clocks to see that they are set and operating properly. The number and length of defrosts can be varied seasonally.

Yearly: Have a professional refrigeration contractor give the system a thorough check-up, paying special attention to the compressors and motors. Check and lubricate fans. Examine refrigerant lines for leaks.

Also, I can’t leave this topic without a short comment on energy conservation. There are a number of general opportunities for energy-saving in refrigeration systems. First and foremost is to buy the correct system, use it correctly and maintain it regularly. A key point to remember when looking at reducing refrigeration energy is that the aim is to save energy, not allow product to degrade or temperatures to fall outside of requirements.

Forensic sanitarian Robert W. Powitz, Ph.D., MPH, RS, CFSP, is principal consultant and technical director of Old Saybrook, CT-based R.W. Powitz & Associates, a professional corporation of forensic sanitarians who specialize in environmental and public health litigation support services to law firms, insurance companies, governmental agencies and industry. For more than 12 years, he was the Director of Environmental Health and Safety for Wayne State University in Detroit, MI, where he continues to hold the academic rank of adjunct professor in the College of Engineering. He also served as Director of Biological Safety and Environment for the U.S. Department of Agriculture at the Plum Island Animal Disease Center at Greenport, NY. Among his honors, Powitz was the recipient of the NSF/NEHA Walter F. Snyder Award for achievement in attaining environmental quality, and the AAS Davis Calvin Wagner Award for excellence as a sanitarian and advancing public health practice. He is the first to hold the title of Diplomate Laureate in the American Academy of Sanitarians, and also is a Diplomate in the American Academy of Certified Consultants and Experts and with the American Board of Forensic Engineering and Technology. Contact him at or through his website at