"Maintaining the cold chain means looking at the entire shipping process from start to finish. Once the products have been cooled, you can never allow them to warm. When the cargo is allowed to warm anywhere in the distribution system, it is almost impossible to cool it back down again. If you let that happen, you will have a negative effect on the quality and the shelf life of the freight." - Professor Jeffrey K. Brecht, University of Florida
This blog is the first of a two-part series taken from our 2020 webinar, Myth versus Fact: The Truth About Refrigerated Shipping. Part two will be posted next week. You can also listen to the webinar here.
Moderator: James Lee, Choptank Transport, Vice President of Legal Affairs
Expert Panelist Jeffrey K. Brecht: University of Florida, professor, and co-author of Protecting Perishable Food in Transport by Truck and Rail.
Expert Panelist Doug Thurston: Emerson, Vice President of Sales
Expert Panelist Greg Blades: Thermo King, General Manager
Myth or Fact #1: All refrigerated trailers built after 1995 have download capability.
Greg (Thermo King): This is a myth. The download capability was an option on units all the way up until the early 2000s. They started becoming more standard equipment around 2004, until around 2006 when it became completely standard and available on all trailer equipment.
Myth or Fact #2: Reefer units are supposed to raise and lower temperatures, right? Kind of like my refrigerator and freezer do at home.
Greg (Thermo King): This is also a myth. The refrigeration units that are on commercial trailers are designed to maintain product temperature, not lower, or raise it.
Moderator: The USDA handbook specifically mentions the fact that reefer units can't remove field heat out of produce.
Jeff (Professor UF): The greatest concern is with fresh produce that is respiring and generating heat. Again, a reefer unit is not designed to cool the product. It is designed to maintain a steady temperature. If you put something into a trailer that hasn't been pre-cooled and still has field heat, it is very likely that it, along with the heat created by respiration, will overwhelm the reefer unit. Rather than drawing the temperature down, you may even see temperatures increasing during transit. It is extremely important that products be pre-cooled before they are loaded onto a trailer because the equipment cannot handle removing too much heat.
In short, inadequately pre-cooled cargo or inadequately pre-cooled trailers are going to affect the temperature of cargo at receiving.
Moderator: What happens when it gets to the receiving dock, and the driver backs up to the dock and is told to open his trailer. The trailer doors sit open while he is waiting to be unloaded. How does that affect the temperature inside the trailer or the product on the tail end of the trailer?
Jeff: (Professor UF): We always talk about maintaining the cold chain which means we like people to look at the entire chain from start to finish. Once the products have been cooled, you should never allow them to warm. Once something is allowed to warm anywhere in the distribution system, it's going to be almost impossible to cool it back down again. Whenever you let that happen, you're going to have a negative effect on the quality and the shelf life of the product.
Doug (Emerson): In the wintertime, you'll have a banana trailer, for example, that is backed into a dock, and it is only 15 degrees outside. The driver backs the unit in and the dock employees open up the trailer doors. The crew then goes on break for an hour. When they come back, they can see from their temperature recording device (TMD) that the temperature has dropped in the back of that truck to maybe 25 or 30 degrees, which can be detrimental to those back pallets of fruit. You wouldn't notice it for three or four days until the ripening process begins. It is not just high heat, but also cold temperatures that play a really important role in the integrity of the product.
Moderator: There are two ways to set a reefer unit. It can be set at start/stop cycle century or continuous. What is the difference between the two?
Greg (Thermo King): Continuous run is going to give you better temperature control overall and is highly recommended for all fresh applications. By running it on continuous run, the continuous airflow of the unit will modulate the temperature much closer to the setpoint. Cycle century is mostly used for frozen applications, and it is mainly a fuel-saving setting. You really do not want to run cycle century in fresh cargo applications at all.
Moderator: How does that affect a TMD that's placed inside a trailer?
Doug (Emerson): There have been examples over the years, most recently in the Midwest, where a shipment of fresh poultry is being dropped at a store. The container sits there for 12 hours before the retailer backhauls it to their distribution center. They have the temperature setting in the truck on start-stop or cycle mode.
Even though they have the reefer setting at 28 degrees, which is what was recommended by that particular retailer, 14 hours later when the product was delivered back at the distribution center, the product actually pulped (and the TMD showed) temperatures above 45 degrees, which obviously is not acceptable for fresh poultry. That gets into the danger level.
There are a number of lessons to be learned here. Understand your delivery times. If a trailer is going to be dropped, try to coincide proper times to pick that truck up to haul it so it never has to sit waiting in the heat, whether it is in continuous mode or not. Also, make sure that your SOPs are being followed. Explicit directions from the carrier and shipper regarding temperature, delivery times, and any other important details should be made crystal clear when the load is tendered.
Myth or Fact #3: The reefer unit on a trailer should be shut off during loading and unloading, or should it be left on?
Greg (Thermo King): It is highly recommended to shut the unit off during the loading and unloading process. A lot of carriers understand this, but a lot of shippers and receivers don't. They think the unit will continue to cool the trailer during that process. When you think about the airflow in a trailer, all it is really doing is blowing the refrigerated air out the back of the trailer. The return air coming back in is whatever's on the dock, whether it be 90 degrees or 30 degrees, so it is not advantageous. You are not helping your product any by running the reefer during the loading and unloading process and you may be hurting it.
Moderator: On a separate topic, what role does a properly installed chute play and maintaining cargo temperature that's open for anybody?
Jeff (Professor UF): If the chute wasn't there, the refrigerated air would have a tendency to return to the reefer unit in the front of the trailer rather than circulating the full length. The air chute promotes proper circulation of chilled air and removes heat from the entire load.
Doug (Emerson): In addition to making sure that the chute is installed and working properly, it is also critical to make sure the load is being stacked inside that trailer correctly. We see cases on a weekly basis where the product is stacked all the way to the ceiling, blocking the flow of the chutes.
Jeff (Professor UF): Cargo should never be loaded right up against the walls of the trailer or to the ceiling. The refrigerated air should be able to envelop the load so it protects the cargo from the outside environment. It is really important that as the shipper, you make sure you understand the proper loading of the truck and that you also understand that trailer itself, how it is designed, and make sure you are following best practices for your customers.
Fresh Produce versus Frozen Food Shipping
Refrigerated trailers were originally designed for frozen foods. The idea was that the chilled air would envelop a solid block of frozen food. When you adopt that technology for fresh produce (which generates its own heat through respiration), you have to get that chilled air into the middle of the cargo.
If you do temperature mapping of fresh produce in a trailer, you'll find that the very middle of the load is going to be the warmest spot because that's where the heat is being generated. It is not chilled as well as it is on the outside of the pallet.
This makes the venting of the cartons for chilled products very important because those vents, from carton to carton, have to line up. This allows the horizontal airflow from the back of the trailer (where it's being delivered) to travel back up to the front. That is how the reefer unit is able to remove that heat of respiration. And if the venting is not designed correctly or the cartons are not stacked correctly, you're going to get hot spots in the center of the load.
Moderator: How can TMDs and Reefer Downloads Assist in Investigating Alleged Temperature Abuse?
Doug (Emerson): There are a million things that can go wrong with temperature-controlled shipping. For example, was the trailer pre-cooled, was the product pre-cooled, was it staged correctly in the right environmental conditions? How old is the trailer, is it air-tight? All these things play a role in the integrity of the product as it travels across the country. Knowing the temperature of the product at all times during the journey is key. And that is what a TMD can do. It can help verify or validate ambient air inside a trailer in different locations.
For example, if a truck is 10 years old, its trailer can lose anywhere from 50% to 70% of its insulation value. That is significant. As a result, you might see a temperature in the front of the trailer at 33 or 34 degrees, but it can be as high as 55 to 60 in the rear of the trailer. This means you have a highly perishable product in the worst possible conditions.
In addition, there is also the potential of driver abuse if he or she is shutting the reefer off to save fuel. Is the truck sitting in the yard too long? Are they opening and closing the doors because of multiple stops? As we just talked about, are they stacking products too high? All these things play a role in the quality and the temperature of a product as it is transported to its destination.
It is really good to use the download of a reefer unit in conjunction with a TMD. To help determine if there was an issue and what the issue was, the unit download is going to be very helpful in securing the data of how the unit was operating, and how it was set. That information will cover the carrier from any liability issues regarding setting the unit incorrectly or determining if the unit was operating properly.
Regarding the reefer unit download, the driver must make sure the timing dates are correct. When reefer units are serviced, make sure you take the opportunity to check the time and dates. Make sure it is correct, because if you ever need to pull a download, and the time and date are incorrect, verification may be difficult.
Have more questions for our experts? Email us at email@example.com. Choptank Transport is an award-winning 3PL specializing in temperature-controlled truckload, LTL, and intermodal freight. We would love to offer you a freight rate. Reach out today.