Keeping Food Safe While Raising Cold-Chain Operating Temperature From -18°C to -15°C (-0.4°F to 5°F)

The May eNews special feature looked at the benefits worldwide of raising cold chain operating temperatures from -18°C to -15°C (-0.4°F to 5°F) to save energy—to the tune of 25 terawatt hours per year. While making this move, it’s estimated that cold chain operators, depending on their role, could save anywhere up to 10% in overall operating costs and make a dent in their carbon footprint.

While the Move to -15°C Coalition has found minimal or no effect on food safety and quality from raising cold-chain temperature by 3°C or about 5°F, it would seem that merely upping thermostats presupposes that instrumentation and equipment can safely hold these higher temps with an adequate safety margin—and that’s assuming that pallet loads are spaced properly to maintain air flow and doors are not left open on trucks and freezers.

FOOD ENGINEERING spoke with a representative from Copeland (previously known as Emerson Cold Chain and Monitoring) and DeltaTrak’s CEO and Founder Fred Wu to get a handle on the ability of the cold chain to keep food safety and quality high at these slightly elevated temperatures.

“It’s important to remember that maintaining food safety and the quality of frozen perishables is still the most critical priority,” says Chris Sercia, Copeland cargo division sales executive. “Older refrigerated trailers (i.e., reefers) have lower insulative values—losing 5 to 10 percent every year—and may simply be unable to maintain proper frozen temperatures with a 5°F increase. Commodities such as ice cream must be held at lower temperatures (i.e., -15°F) to maintain their ideal whipped consistency; any increase in that temperature over a prolonged period would likely violate brand quality standards. So, if you were to ship ice cream in a 10-year-old truck during the heat of the summer—and hypothetically increased the temperature to -10 °F to save energy— you could experience poor results.”

For commodities such as chicken that are held within a typical 0 to 5°F range, the consequences of an incremental temperature increase could cause potential food safety issues, Sercia says. “For example, even though the reefer setpoint temperature may indicate 5°F, poor insulation combined with tightly packed loads could cause the actual circulating air temperature to be 10 to 15°F higher. This could result in defrosting and thawing, which could, at best, impair quality and, at worst, create the potential for bacterial formation.”

“On the surface, ‘just turning up the thermostat,’ does seem like a simple solution to help reduce emissions across the cold chain, but it is not as straightforward as it seems,” says DeltaTrak’s Wu. “So first, we need to frame the issue of emissions within the food system.”

According to Wu, the supply chain only accounts for 18% of emissions, whereas 24% comes from land use and deforestation and 58% from farming. “Most sources quote that 40% of our food is wasted. I would argue that the most significant impact in carbon emissions will come from reducing food waste,” says Wu.

Frozen foods, Wu says, have traditionally been less susceptible to food safety concerns than fresh food, which present more significant challenges. “Fresh produce is particularly complex as each commodity has a government mandated safe zone for temperature management. Not only do you need to be concerned about food safety, but also food quality, which will depend on several factors including: cut-to-cool time, supply chain temperature management and shipment journey time. For instance, when avocados are transported from Mexico to the USA, the temperature of the transport container or train is set to help avocados ripen during transit while maintaining freshness and safety. More information can be found using the Federal Drug Administration (FDA) Risk-Ranking Model for Food Tracing (RRM-FT), which provides risk scores for all commodities and provides a risk curve associated with various temperatures,” Wu says.

Setpoints and Accuracy

Typically, in a reefer, the temperature sensors are built into the supply air reefer unit where the thermostat is located, Wu says. When the thermostats turn the reefer unit off and on, it creates a defrost cycle. Some equipment can operate within a ±2°F, and other older equipment may be less accurate and work within ±5°F, Wu says. Since the thermostat is located in the front, and the cargo temperature is higher at the back by at least 5°F, it’s necessary to set the thermostat at least 5°F colder to compensate for this well-known issue.

Ice cream is one of the primary indicators of problems during the defrost cycle, Wu says. If ice crystals formed on the lid of the container, consumers will know that it has partially thawed during a defrost cycle, and while not a food safety problem, it is a selling issue, leading to rejection by the consumer.

Over-packing and poor pallet loading practices can restrict airflow and increase reefer air temperatures—while unintentionally creating temperature variances throughout the trailer, Sercia says. It’s important to remember that reefers are designed to hold—not cool—perishables, so proper cold chain shipping starts by pre-cooling products to the ideal setpoint. Then, pallets should be loaded in a centerline configuration and locked into place to allow for sufficient air circulation throughout the trailer.

Monitor Product Temperature—Not Ambient

McDonald’s was the first innovator to design, develop and implement a new food safety temperature standard at scale, Wu says. Around 10 years ago, McDonald’s asked DeltaTrak to help them record the actual product temperatures across their entire operation, which includes shipping, delivery, handling, storage and processing. This led to McDonald’s changing their quality reference for temperature from ambient temperature to product temperature.

In one delivery, the driver had left the back door open for 15 minutes to an ambient 85°F temperature. By using the product temperature for the quality alert reference rather than the ambient temperature of the truck, McDonald’s was able to eliminate many nuisance alert reports and better focus on the actual product temperature conditions that may impact food safety, food quality and shelf life.

Supply Chain Temperature Issues

Increasing setpoints by 3°C or 5°F is not the challenge; the challenge is making sure all other factors are in place to reliably implement a temperature increase without risking perishable quality and food safety, Sercia says. “Considering all the variables in the over-the-road trucking sector, even this slight temperature increase may leave less room for error—especially in warmer regions or seasons where a trailer’s insulative capabilities are often put to the test. For example, if the reefer download temperature is raised by 5°F, and the trailer can barely hold that temperature in the heat of the summer, and then the trailer sits with open doors for two hours to unload, operators could be facing significant perishable degradation. The best-case scenario would be to have the product as cold as possible at the point of delivery; even a slight temperature setpoint increase may disrupt that balance.”

Achieving a consistent and food-safe temperature requires careful monitoring and management, Wu says. This involves strategically located sensors throughout the trailer space and real-time loggers to maintain the desired temperature for food safety. 

DeltaTrak has several partners that are exporters out of Chile, which face several trade lanes with extended journey times, Wu says. “These exporters use a two-channel, real-time logger with a 15-meter cable sensor in the supply air duct in the front of the reefer to measure the cold air coming in and simultaneously record the cargo temperature at the back of the container. Typically, they should not see a delta-T of more ± 2°C. Suppose the contracted supply air temperature is not maintained. In that case, they will see an incremental rise in the cargo temperature in the back, which will clearly indicate irregularity when filing a claim and will impact food quality and safety concerns.”

There are several cases of maritime lines or ports mishandling containers, Wu says. For example, trucks may turn off power to reefers to save energy while waiting for berthing, and power to the containers may get disconnected during the unloading or inspection process. Declaring carbon emissions is mandated now by European law, and this puts pressure on the supply chain to decrease the fuel to keep products frozen.

“Since we are in a global economy where food items are shipped worldwide, a global standard needs to be set, and actors in the industry will need to provide data by using cold chain compliance track and trace solutions,” Wu says. As this data is gathered and used for analytics purposes, it will also demonstrate and give evidence on whether increasing the temperature by 5°F (3°C) will have decreased carbon emissions while maintaining safe food.

When all is said and done, the market will help make the decisions, Wu says. “When influential food retailer customers like Kroger, Costco and Publix embrace the use of advanced technology to get better visibility of their cold chain performance, especially in real time, the concern over increasing the temperature by +5°F may become less of an issue as they can see what is or is not being impacted.”