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From: Food Quality & Safety magazine, August/September 2007

Cool Technologies

Logistical and monitoring solutions can facilitate better cold chain management

by Thomas Jensen

Most of us can recount opening a recently purchased food product, only to find it spoiled. This firsthand experience underscores ongoing problems within the food supply chain that new technologies can solve.

Maintaining proper temperature during handling is fundamental in ensuring the quality of perishable products. Exposures over and under safe temperature limits lead to spoilage or loss of freshness. Poorly handled products can result in rejected product, customer dissatisfaction, illness, and even loss of life.

A supply chain is referred to as a “cold chain” when transport of perishable products is involved. Spoilage problems faced by cold chain managers stem mainly from the fact that, at different points along a supply chain, products change hands many times; there are gaps in any one party’s knowledge of the environment the products are exposed to during transport. Many times, there is no single party to blame, nor can liability be assessed, because there is usually no recorded temperature history to tell what went wrong or when it happened.

Companies Absorb Losses

In most of the food industry today, spoilage problems remain open-ended, and companies are absorbing the losses. Perishable foods constitute the single largest category within a conventional supermarket chain, contributing to approximately 35% to 50% of sales and 40% to 55% of gross profits. Freezing conditions can also adversely affect some products and can cause a significant problem in many regions during colder months. More often, though, excessive heat leads to quality problems during food transport and storage.

As an example, the useful shelf life of fresh picked strawberries falls dramatically as temperatures increase (see Figure 1, right).

Growers and shippers go to great lengths to keep products such as strawberries close to their ideal temperature. Yet many temperature abuses occur on the trip from producer to distribution center to supermarket: A truck’s refrigerator unit may get turned off inadvertently, or a delivery gets left on a hot shipping dock before it is brought inside. Figure 2 (p. 27) shows an example of temperature history for a strawberry shipment, where the measurement is taken inside the product carton that was loaded on a pallet of product.

Note that the high and low limits are +39°F and +32°F—the recommended temperature range for handling strawberries. The chart shows that as the shipment progressed, the refrigerator unit did not maintain the product under its maximum limit—likely due to summer temperatures and pallet organization. The data show that the product was unloaded on the morning of June 9 and sat for approximately eight hours in a receiving area. Time out of refrigeration added to the already compromised condition of the product, resulting in an even shorter shelf life and lower customer satisfaction.

As products change hands on their way from production to point of purchase, each transition in the cold chain is another chance for temperature abuse, and each is cumulative. Perishable products lose shelf life in relation to time out of specification and in relation to the difference in actual versus desired temperature at any given time. The longer the time out and the farther it is out of range, the more spoilage will result.

Shipping and handling abuses are common—especially in summer—and, in many cases, abuses are far worse than the one in this example. Freezing conditions during colder months or caused by refrigerator units set too low also cause substantial losses for a wide variety of food products.

The lack of visibility into the causes of such events has been, until recently, a problem that supply chain managers have not been able to solve. Whether the problem occurs with produce, fresh prepared foods, or meat and seafood, avoiding food spoilage through proper cold chain management is crucial to maintaining quality, value, and safety. Without visibility, losses of product are substantially greater, as are the risks to product safety and brand image.

Some methods to prevent abuses in the cold chain are:

Logistical Solutions

Supply chain managers today use several low technology approaches that are popular and effective at extending the life of refrigerated products.

One method is pre-cooling, in which a product is brought to a lower temperature by producers prior to loading into refrigerated containers. Pre-cooling removes latent heat and effectively extends product life. The transport refrigerator is not designed to remove excess heat from a pre-cooled load but rather to maintain an acceptable temperature range. Pre-cooling also reduces moisture that would otherwise be present, which keeps shipping cartons dry and strong, and—in the case of fresh foods—prevents unwanted microbial growth. Many producers use drying/chilling processes to effectively remove moisture as a product is cooled.

During the loading of refrigerated pallets, placing products properly by creating gaps between pallet rows allows refrigerated air to circulate freely through the load. Many refrigerator units blow air out of a single duct from the top front of the container, across the tops of the pallets. Tightly packed pallets refrigerated in this way suffer from a false floor: air above the pallets is the proper temperature, but the temperature remains elevated down in the load. Some refrigerated containers feature air ducts for distribution of supply air and return air down the sides of the space, which helps to equalize temperature. Cartons with air ventilation holes in the side panels also promote good air circulation in the pallet and reduce the possibility for condensation around or on the product.

Take precautions during loading and unloading to prevent refrigerated product from becoming exposed to non-refrigerated air temperatures (as is the case in the shipment temperature example in Figure 2). Avoid placing refrigerated pallets on an open shipping dock for any period of time — especially when product is changing hands. This happens when, for example, a truck is unloaded, the shipment is signed for, and the driver leaves. Then perhaps the dock crew breaks for lunch or a shift change. When such events occur, the producer/owner of the product rarely has visibility as to the problem until the later point of pain (e.g., when the retailer returns the product or when the consumer rejects it as second rate or spoiled).

Monitoring Solutions

To gain visibility into the cold chain, many supply chain quality assurance (QA) managers require that one or more temperature monitors be included with each container shipment. They typically request that the device or its data be returned from the destination. These monitoring devices are referred to as temperature data loggers or temperature data recorders. They can be electronic or mechanical.

Mechanical recorders, such as the Ryan recorder, save a basic temperature history on a strip chart. Electronic data loggers take more accurate periodic temperature readings and store them in memory. One or two monitors per load are typically placed on top of pallets or attached to the sides.

Examples of these types of products include those from Cargo Data Management Corp. (Irving, Texas), DeltaTRAK Inc. (Pleasanton, Calif.), Pace Scientific Inc.(Mooresville, N.C.), HOBO (Bourne, Mass.), and Sensitech (Beverly, Mass.). They typically share the following properties:

  • Cost $15 to $175 each;
  • Must be programmed prior to use to establish upper and lower temperature set-points, periodicity, and other variables;
  • Are reuseable/rechargeable; and
  • Send data from a destination point to the owner’s QA contact.

Newer monitoring devices feature active radio frequency identification (RFID) technology, which allows a wireless data link to be established directly between the product and local readers. Some devices track temperature and upload it upon reading. These incorporate a battery and cost $22 to $250 each. A growing list of companies, including Sensitech and Intermec (Everett, Wash.) offer such products. As for active RFID readers, some are handheld and others are mounted on conveying systems or product portals. When a tagged product passes a reader, product data are read.

Each of these available technologies offers reliable and useful tools that can help supply chain managers move toward better control of their products. Drawbacks exist in implementing applications in supply chain management, however. Both conventional data logging and active RFID monitoring products are limiting in the following ways:

  • Significant efforts are required to integrate monitoring into existing IT and cold chain management practices when first implementing an overall program;
  • Cost per use is high due to cost per tag, cost per reader, return charges, reprogramming, recharging, and logistical details associated with reusability of data loggers;
  • Co-locatability of multiple active RFID tags is problematic and requires higher cost readers for higher densities of tags;
  • Extensive additional information infrastructure and information management are required; and
  • There are added associated labor costs, and an additional technical level of expertise is required on site for proper implementation and analysis of data.

Smart Labels/Tags: Better Monitoring

Newly available temperature monitoring smart labels and tags are changing temperature monitoring in the supply chain. Label and tag products offered by companies such as PakSense (Boise, Idaho) and InfraTab (Oxnard, Calif.) feature embedded electronics with power sources. They can be used to monitor the temperature of perishable goods throughout an entire distribution cycle.

PakSense smart labels are set to acceptable temperature range specifications, which are programmed into each label at time of order. These labels can be affixed to cartons or pallets or can be placed directly against target food products. The user snaps the corner of a PakSense smart label to activate it. The user can then attach it to cases or pallets of product prior to shipment. Data from the smart label are indicated on the label surface, and detailed download data are available through a portable label reader. The smart labels are low in cost and promote broader sampling.

InfraTab’s Freshtime RFID tag products store temperatures and can be read using their RFID readers. Freshtime tags can either be applied as a single use per pallet or case, or as multi use tags for reusable containers and closed supply chains. They can also be used as “standalone” tags with on-tag display or in conjunction with RFID handheld or portal readers.

In conclusion, emerging technologies are improving food quality, and this trend will continue. The producer, the distributor, the retailer, and the consumer are all demanding that their food arrives fresh and safe. New technologies will help assure more profit, more branding opportunities, and healthy, satisfied consumers.

Jensen is founder, chairman, and chief executive officer of PakSense (Boise, Idaho). Reach him at (208) 629-3358.

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