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April 28, 2020

What Is Time/Temperature Control for Safety (TCS)?

Written by SmartSense | Food Safety, HACCP

The traditional definition of “perishable foods” has been revised over the years to reflect scientific and technological developments. “Perishable foods” broadly emphasizes the idea that food such as raw meat or produce eventually spoils, but without any connotation regarding safety. Once the number and severity of food recalls due to foodborne illness became more common as a public health issue, perishable foods were redefined as “potentially hazardous foods” (PHF) to acknowledge the new concerns.


Most recently “PHF” has undergone yet another transformation. Increasingly, the new term used is “TCS,” or foods requiring time and temperature control for safety. This change emphasizes not merely the potential existence of unsafe pathogens, but the two primary ways to control contamination in the first place—that is, the solution rather than merely the problem. Several factors affect the rate at which pathogens grow in food, but time and temperature are two of the most easily-controlled factors along the supply chain. “TCS” thus reflects the shift from reactive to proactive approaches to food safety initiated by passage of FSMA.


Recognizing TCS Food

Consumers are demanding TCS food items year-round at grocery stores, restaurants, and other outlets that provide ready-to-eat meals. They’re more discriminating at point of sale, seeking out food items from retailers they trust will deliver a safe and quality product. For this reason alone, managers and staff must be mindful of all of the points along the supply chain when and where TCS foods are at risk for time and temperature excursions.


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TCS food can be raw plant or animal food, such as Romaine lettuce or chicken breasts, or it can be prepared foods, like macaroni and cheese or a burrito bowl. In general, TCS foods have high protein levels, are less acidic, and contain moisture. More specifically, the most common TCS foods include:

  • Milk and other dairy products
  • Meat (beef, pork, lamb) or poultry (chicken, turkey)
  • Fish and shellfish
  • Eggs
  • Plant-based foods that have been heat-treated (cooked rice, beans, or vegetables)
  • Soy foods (tofu, textured soy protein)
  • Sliced or cut fruits or vegetables (e.g. melons, leafy greens, tomatoes)
  • Bean sprouts and sprout seeds
  • Untreated garlic-and-oil mixtures


Why TCS Foods Are Potentially Hazardous

There are six factors that affect bacterial growth in food: time, temperature, moisture, acidity, nutrients, and oxygen. TCS foods are the most likely to be affected by all six factors, and thus are most at risk for bacterial growth. Small amounts of pathogens in TCS food are typically not a problem, but too many can cause foodborne illness. Add time and warmth to the mix, and these foods can become bacteria breeding grounds.


Bacteria tend to grow in foods with a pH between 4.6 and 9.0. Low pH foods are more acidic, and include pickles, jam, honey, and fruit. High pH foods lack acidity and include meat, milk, and vegetables.


Bacteria need moisture to grow, which is measured by water activity. The higher the moisture in a food, the better the conditions for bacterial growth. The water activity scale ranges from 0 to 1.0, with distilled water being 1.0. Most foods have a water activity of at least 0.95, meaning that bacteria have sufficient moisture to grow.


A food handler cannot control a food’s acidity or moisture; these properties are inherent to the food itself. However, along the food supply chain, the remaining two factors, time and temperature, can be controlled.


The need for time/temperature control is primarily determined by the potential for pathogenic contamination and the subsequent growth of microorganisms. The following factors must always be considered when determining whether a food requires time/temperature control during storage, distribution, and handling to assure consumer protection:

  • The kind and number of initial microorganisms present
  • The composition of the food (moisture, pH, acidity, nutrient content)
  • The processing methods (heating, cooling, thawing, holding)


Time and temperature are closely related. Bacterial growth in ideal conditions happens rapidly: the number of bacteria can double every 15 to 20 minutes. This is especially true when the temperature of TCS food falls in the temperature danger zone (41-135° F) for more than four hours.


Time as a Food Safety Control

After four hours in the danger zone, most TCS foods will contain enough bacteria to cause a risk for foodborne illness. Therefore, hot/cold ready-to-eat foods that are not temperature controlled should be consumed or reheated/chilled within 4 hours. After that, they should be discarded.


Time alone, at ambient temperatures, may be used to control the safety of products, but requires great care and attention. The duration should not be greater than the “lag phase” of the pathogen in the product. During this lag phase, the microorganisms assimilate nutrients and increase in size.


The lag phase of a microorganism depends on temperature; therefore, for a specific TCS product, the shelf life or use period required for safety may vary depending on the temperature at which the product is stored. Generally, as storage temperature decreases, the lag phase extends and the rate of growth decreases.


TCS foods that begin cold and remain cool may be held at room temperature longer. Cold foods can usually be served for six hours as long as the food temperature stays below 70° F. However, if the temperature of cold food is not regularly checked, it should be discarded after four hours.


The 2 Hour / 4 Hour Rule explained. Source: https://www.sahealth.sa.gov.au/wps/wcm/connect/3dd213804376220b92dcdfc9302c1003/2+hour+4+hour+Rule+%28poster%29.pdf


If using “time only” controls, it’s imperative to fulfill these minimum requirements:

  • If foods are cooked, cooled and kept cold before being held, written procedures must be available for each process.
  • Temperatures must be monitored and recorded for the cooking, cooling and cold holding processes to ensure the foods reach the proper temperature within the required amount of time and are held at the proper temperature.
  • The foods must be marked or identified to indicate when time control begins and when the time limit expires. Foods that are not marked or identified as required must be discarded.
  • Foods must be discarded when they have reached the time limit (4 hours or 6 hours).


Temperature as a Food Safety Control

Clearly, a “time alone” strategy is prone to human error and thus is a riskier form of food safety control. Time in combination with temperature offers a much more accurate and reliable approach.


There are four food temperature zones that are important to know:

  1. The Hot Zone: 60° C/140° F and above is known as the hot food zone. As a general rule, food should always be cooked to 74° C/165° F (or higher) but must not drop below 60° C/140° F when being displayed or served.
  2. The Cold Zone: 0° C to 4° C/32° F to 40° F is the cold food zone and is the normal temperature for most refrigerators.
  3. The Frozen Zone: Frozen food is normally held in freezers at -18° C/0° F (or lower).
  4. The Danger Zone: TCS food is therefore at risk between 4° C and 60° C/40° F to 140° F.


Fluctuation of temperature readily occurs during storage, transport and retail display, thus greatly impacting the growth of microorganisms. To further complicate matters, each type of microorganism has its own preferred growth temperature range known as minimum, optimum and maximum temperature.


Receiving Food

It’s important to make sure you check and document the temperature of TCS food during the receiving process. This will help you gauge whether food was exposed to the temperature danger zone during transit.

  • Refrigerated TCS foods should arrive at 41° F (5° C) or colder.
  • Frozen TCS food should arrive at 0° F (-18° C) or colder.
  • Hot TCS food should be received at 135° F (57° C) or higher.


Storing Food

Regularly monitoring and recording temperature during storage of TCS food is very important. The proper temperatures for kitchen equipment are as follows:

  • Refrigerators: 40° F (4° C) or colder
  • Freezers: 0° F (-18° C) or colder
  • Dry storage: 50° F to 70° F (10° C to 21° C), with relative humidity of 50 to 60 percent


Proper storage best practices for TCS food include the following:

  • Refrigerated TCS food should be stored at 41° F (5° C) or colder so that the internal temperature of the food maintains this temperature.
  • Do not overcrowd freezers, which can increase the internal temperature, causing the food to thaw.
  • Ready-to-eat food prepared on-site must be used within seven days if held at 41° F (5° C) or lower.


Cooling TCS Foods

When cooling foods, the FDA Food Code recommends a two-stage cooling process:

  1. The food should first be cooled from 135° to 70° F in two hours or less.
  2. Next, the food should be cooled from 70° to 40° F in four hours or less.


Total cooling should not exceed six hours. The best ways to cool foods rapidly include using an ice bath, transferring the food to a shallow pan, or dividing dense foods, like a casserole, into smaller portions.


Reheating TCS Foods

Because foods must be reheated quickly, it is important to use appropriate cooking or rethermalizing equipment such as a microwave, stove, or oven. Do not attempt to reheat food for hot holding in warming trays or other hot-holding equipment because these devices will not warm up the food fast enough and will allow pathogens to grow.


When reheating food, the internal temperature of the food must reach 165° F (74° C) for at least 15 seconds within two hours. Once this minimum temperature has been reached, the food should be held at 135 ° F (57° C) or warmer.


Holding TCS Foods

Once a TCS food has been cooked, it must be held at the correct internal temperature. Cold TCS food must maintain a temperature of 41° F (5° C) or colder, while hot TCS food must maintain a temperature of 135° F (57° C) or hotter. Temperatures of held TCS food should be taken every two hours. Any prepared food that falls in the temperature danger zone (41° F - 135° F) for more than four hours should be discarded.



Given the complexity of time and temperature coordination to keep TCS foods in compliance with the food safety standards of FSMS, documented procedures and digital technologies should be incorporated into your Food Safety Management System (FSMS). An FSMS is critically important to help any food business to protect customers from food safety risks, including food poisoning or allergic reactions.


While not yet explicitly required by FSMA, temperature-monitoring digital data loggers simplify the process of assessing the condition and status of food products, which lets you react fast to changes in temperature or product quality, thus avoiding the potential setbacks of contaminated goods. With accurate temperature monitoring via data loggers, you can trust your company will meet FSMA’s requirements.


Wireless temperature sensors provide accurate readings at multiple sites in a facility and can run continuously for years without a battery change. Additionally, because digital systems monitor temperature in real time, they can sound an alarm if the temperature isn’t being properly regulated, so that safety managers can deal with the issue right away. Data loggers also collect and store recorded times and temperatures in a cloud-based system that enables sophisticated analysis and timely, accurate compliance reporting.


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Topics: Food Safety HACCP

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