Thermal Mapping Studies: A Data-driven Approach to Root Cause Analysis

At Sensitech^®, many of our customers rely on our Professional Services team to gain evidence-based insights to continuously improve their supply chains.

For instance, our food customers are concerned about preserving the quality of temperature-sensitive products while they are in transit from source to consumer. Many of them have asked us to uncover root causes of temperature excursions that have caused damage to product during the shipping process.

Others want to explore new approaches for improving product quality. For example, a major quick-serve restaurant chain recently asked us to research the impact of a process variation for how some of its bakery products, specifically two types of sandwich buns, were frozen and shipped. The customer had been freezing the buns at the bakery prior to shipping and wanted to explore what would happen if they shipped the products fresh and froze them while in transit. The decision to freeze product during transport needs careful consideration as transport refrigeration equipment is typically optimized to hold product temperatures consistent during the journey, to save weight and fuel.

Determining optimal freezing parameters

Previous Sensitech fieldwork has shown that it is important to minimize the amount of time starch-containing products stay in a refrigerated environment, as refrigeration can accelerate staleness. Therefore, we typically recommend that bread should either be:

1. stored fresh at room temperature where possible to maximize shelf life or,
2. if product is frozen, it should be frozen and thawed quickly to minimize the time spent in refrigerated conditions.

Hand in hand with this research, other studies have found that using refrigerated shipping containers to cool or freeze product while in transit, rather than maintain temperature, may be detrimental to the quality of certain products.

This particular customer wanted to test the quality impact of freezing its bread products during in-transit ocean shipments and understand if time-to-delivery improvements might be gained.

Using thermal mapping for fact-based evidence

The thermal-mapping process for this specific scenario provided real-time data on:

• How long it took the product to freeze.
• If temperature uniformity was achieved inside the cases over the course of the shipping route.
• The overall impact of the process on quality.

The process began on site at the supplier, a bakery in California, where the bread products were made, put into plastic bags, and then into cardboard cases. The cases were stored in ambient conditions at the bakery for 24 hours, before being shipped by ocean liner to the chain’s distributor in the Hawaiian Islands, and then onto its restaurants.

Image 1: Packaged buns with TempTale^® monitors

Prior to the products leaving the bakery, Sensitech was on site to strategically place 36 temperature dataloggers inside the product cases. The cases were then organized onto six pallets. The team used single-sensor probes in the middle cases on the pallets and dual-sensor stainless steel monitors in the ones nearer the outer edges. The dual-sensor monitors measured both product temperature inside the cases during shipping, as well as ambient temperature outside of them in the shipping container.

Image 2: Location of monitored and unmonitored buns in container by type of bun

The monitors collected temperature data from the time the goods left the bakery in California until they arrived at the distribution center in Hawaii. From the data collected during the shipping process, Sensitech determined:

• What temperatures the products were exposed to during the entire time in transit.
• How quickly the products froze and if they remained frozen during the entire shipment.
• How freezing variations occurred a) within each individual pallet and b) based on pallet location within the container.
• How the process affected the product upon arrival as its final destination.

Driving better results with real-time data

The thermal mapping study collected real-time data throughout the entire shipping journey; the data was correlated with our customer’s objectives. For instance, the standard temperature this customer used for freezing its product was 20°F. We correlated that with the shipping container’s set point of -10°F, which was reached the second day of transit.

Here is an overview of what we discovered in relationship to those set points:

• Over the course of the seven-day shipment, there were ambient temperature variations throughout the cases, from floor to ceiling, with the cases in the middle of the pallets remaining the coldest.
• There were daily variations in product temperature over time, from 75°F initially at the bakery to, in some instances, below -5°F, which occurred on day seven of the shipment.
• Product near the core of the pallets reached the ideal 20°F in an average of 1.9 days, with the longest layer achieving that temperature in 3.8 days for one product and 2.6 days for another. Product at the corners reached that temperature in 0.7 days.
• By applying a weighted average, the data indicated that the time required for the average bun inside the case to reach 20°F took about two days.
• Regardless of bread type, time to 20°F varied widely throughout the cases and depended more on product location within the pallet rather than location inside the cases.

Image 3: Graph showing length of time needed for buns to reach 20°F

Enabling better decision making and improved product quality

Based on the data collected and on-site observations, Sensitech provided the quick-serve restaurant chain with insights that would help them decide whether to further explore this option. Sensitech offered several suggestions on how, if the customer pursued this approach, the overall results and product quality could be improved.

Loading Configurations

• There could be more uniform temperatures throughout the cases if airflow increased between the pallets by adjusting the loading configuration to reduce open floor space in the container. Typically, cold air flows from the floor of a container to the ceiling, following the path of least resistance. Therefore, if the amount of empty space in the trailer were reduced, the air would be forced through pallets rather than open spaces.

Packaging

• These particular products were shrink-wrapped on the pallets. By utilizing pallet corner boards and straps instead of shrink-wrap, the pallets would be kept in place during transport and allow for increased air flow through cases and faster freezing of the products.
• Because products were in cardboard cases with minimal openings, there was limited air flow. A more optimal option would be cardboard boxes with air holes, or reusable plastic containers (RPCs), both of which would increase air circulation and product temperature uniformity throughout the pallet.

Product Location

• Product located in the middle layer of cases in the core of the pallets took up to two days longer to freeze compared to the pallet exteriors. Using a chimney in the center of the pallet would increase air flow through the core cases and reduce freezing times.

With this information, the customer can now make a better-informed decision on whether or not the tested process, with these additional recommendations, would be a viable process moving forward. The chain can weigh whether freezing the products in transit rather than prior to shipping significantly improved the overall process without compromising product quality upon arrival at its restaurants.

For more information on Sensitech’s thermal mapping studies, visit our Professional Services site or contact us here.