Time and Temperature: Why 41°F to 135°F?
In one of my last blogs, I mentioned the temperature danger zone, or TDZ, as those in foodservice often refer to it. Learning the TDZ is almost a rite of passage for any new employee. Most could recite it in their sleep: “41°F and 135°F, the zone where bacteria multiply quickly.” In the foodservice environment, the TDZ isn’t just a best practice; it’s a critical defense against foodborne illness. Failing to manage time and temperature properly can lead to serious health risks, liability, and damage to the reputation of your brand.
The FDA Food Model Code sets strict guidelines: cold foods must be held at 41°F or below, and hot foods at 135°F or above. Any food that remains in the TDZ for more than 4 hours cumulatively must be discarded.
Early in my days in the industry, when I was just a teenager getting my first job, I was taught about the TDZ. What we, or at least I, didn’t understand back then was just how difficult it is to keep food out of this dreaded TDZ. For example, I don’t know if we (my fellow employees and I) fully appreciated the cooling curve for products such as soups and gravies. We would batch cook most of our soups, cool them down, and then reheat them for later service. I vividly remember being trained to take the soup off the steam-jacketed kettle at the end of the cooking process, divide the soup into two-gallon Cambro containers, and leave the lid slightly ajar so the initial heat could escape, and placing them on the counter (not in the cooler) for a half hour or so for initial cooling. After all, we didn’t want to warm up the cooler. Then, after a half hour or so, I was trained to place the product in the cooler with the lid covering the product tightly and let it cool. I know practices have changed at that operation, but back then, we thought the soup would be just fine! Now, we know that the two gallons of soup would never cool within current food code guidelines and would be within the TDA for far too long.
What I find when I conduct employee training is that most employees appreciate the TDZ and can recite it like the Pledge of Allegiance, but they really don’t understand it. I mean, truly grasp why that range was established and codified.
To fully understand the TDA, it helps to know a bit about food safety history. Although President Lincoln established the United States Department of Agriculture and the Division of Chemistry (which later became the Food and Drug Administration), public health officials really became serious about food safety in the early 1900s with the passing of the Pure Food and Drug Act. The Act was passed, in part, because of the public outcry following the publication of The Jungle by Upton Sinclair.
In the 1940s and 1950s, increased attention to military food safety intensified during World War II and the growth of industrial food production. These developments led to increased scrutiny of food handling, including time and temperature controls.
Then, in the late 1950s and early 1960s, we began to see food codes mentioning temperature criteria, which at that time were identified as either 40°F to 140°F, 45°F to 140°F, or 40°F to 150°F, depending on the source that you reviewed. These early references laid the groundwork for the standardized temperature danger zone we recognize today.
…If you have been in the industry for a while, you might recall the old TDZ to be 40°F to 140°F, which was always easily memorable in my mind. So why the change to the current 41°F to 135°F? Well, it wasn’t arbitrary…
First, it is important to understand that the food code is a mix of science, feasibility, and usability. The code document has a tough job; it must take the best of what we know about science, epidemiology, and technology; understand what is achievable in real kitchens with equipment limitations, labor constraints, and operational complexity; and make it clear enough that a foodservice manager can understand it and a regulatory official can enforce.
What was found in the scientific community about the TDA was that most common foodborne pathogens (like Salmonella, E. coli, and Listeria) grow most rapidly between 41°F and 135°F. The difference between 135°F and 140°F was not significant in the overall growth of microorganisms. Conversely, at the cold end, pathogen growth is not much different at 41°F versus the previous 40°F.
From an operator’s perspective, commercial refrigerators were more reliably able to maintain 41°F than exactly 40°F. Thus, it is easier for facilities to consistently meet and monitor 41°F. Similarly, hot-holding equipment like steam tables often stabilizes at a holding temperature of 135°F, whereas 140°F is more difficult to achieve.
Thus, the adjustment to the TDA we know today was made because of increased knowledge of pathogen growth, while trying to make the code more practical for foodservice operators to comply with, while not compromising public health.
Understanding and respecting the TDZ is one of the most important responsibilities in foodservice. Make temperature control a daily habit, build a culture of food safety, and invest in the right tools and training to ensure that your operation stays safe, compliant, and trusted. Risk Nothing.
READ MORE POSTS
Foodborne Illness Myths & Facts
“It must have been something I ate.” That’s the typical statement when a person develops some relatively minor symptoms from food. Maybe not severe enough to go to the doctor so you choose to tough it out without medical care. Sudden onset of flu-like symptoms such as onset of stomach cramps, diarrhea, vomiting and fever could possibly mean you are the victim of a foodborne illness. The illness is sometimes referred to as “food poisoning”, but it’s often misdiagnosed.
Don’t Compromise: Clean and Sanitize
The subject is cleaning and sanitizing. Chefs, food service directors, managers and staff try to practice safe food-handling at every turn in the kitchen. Don’t let that effort go down the drain by slacking off on the many aspects of sanitation. That includes dish and ware-washing techniques (pots, pans, equipment), and cleaning all the areas that give us that “neat as a pin” appearance in your customers eyes. Customers seldom fail to bring that soiled silverware or glass with lipstick on it to the attention of the manager or wait staff. Improperly cleaning and sanitizing of food contact equipment does allow transmission of pathogenic microorganisms to food and ultimately our customer.
The Route to Safer Fresh Fruits and Vegetables
Although fruits and vegetables are one of the healthiest foods sources in our diet, we continue to have foodborne disease outbreaks of significance from produce, sometimes affecting large groups of people in multiple states because of their wide distribution. The CDC estimates that fresh produce now causes a huge number of foodborne illness outbreaks in the United States. Produce needs our continued food safety efforts at the restaurant level as well as at the stages in agricultural production. Occasionally, fresh fruits and vegetables can become contaminated with harmful bacteria or viruses, such as Salmonella, E. coli 0157:H7, Norovirus, and Hepatitis A. This contamination can occur at any point from the field to our table. If eaten, contaminated fruits and vegetables can cause foodborne illness.
Be Cool, Chill Out, Refrigerate Promptly!
The Cold Chain -- Keeping perishable foods at proper cold holding temperatures (between 28°F and 41°F maximum or 0°F for frozen food) from your food producers / manufacturers to your customers has to be one of our strongest links to safe food and high quality. Sometimes that is referred to in the food industry as “maintaining the COLD CHAIN”. Any slip ups in the cold chain, and we have a weak link. Most all of our state food regulations require 41°F as a cold maximum, but colder is a “best practice” policy to maintain.
