Proper Produce Pulping and Mixed Loads

Posted by Harriet Mills on Jul 30, 2020 9:09:53 AM

proper pulping

What’s the big deal about pulping?

Taking temperatures isn’t just something you should do for COVID-19. It is an essential part of shipping produce on refrigerated trucks. In the logistics industry the process is called pulping, and it is the act of taking the fruit’s or vegetable’s temperature during various stages of the shipment.


If God had written ten commandments for shipping produce, the first commandment would be, “Thou shalt not put a warm load of melons straight from the field into a pre-cooled truck and expect it to deliver on-temp.” Every cold chain shipper should know this.


The misconception that a reefer trailer will cool down a product to the required specified temperature has gotten many shippers into trouble. Carriers are not responsible for a product’s initial pulp temperature prior to loading – they are only responsible for maintaining consistent air temperature inside the trailer.  Again, carriers are not responsible for a product’s initial pulp temperature prior to loading, but only for maintaining constant ambient air temperature within the trailer. It is the shipper’s responsibility to ensure that the product is already at the requested receiving temperature at the time of loading.


Whose job is it to pulp—the carrier, driver, receiver or shipper?


Shippers should always pulp the product before loading and preferably do so in the presence of the driver. It can be done by using a digital thermometer or by a probe thermometer. Probes are more accurate, but because they pierce the product’s skin, some prefer to go the digital route. Temperatures should be documented on the shipment’s bill of lading and signed by both the shipper and driver. Pulping at the shipment’s place of origin helps protect both the shipper and carrier from claims if the product arrives at its destination and pulps off-temp.


Read our blog post: Food Waste in the Supply Chain


Responsibility falls on the driver/carrier for having their equipment serviced regularly and for checking the reefer unit and trailer for leaks and malfunctions before loading. Monitoring temperatures while in transit can be done in several ways. Newer technologies provide a combination of GPS tracking with temperature sensor monitoring so that if the cargo experiences a temperature change, the dispatcher or fleet operator is alerted. Older reefer units may only have the temperature download information on the unit itself. Some shippers prefer to rely on a secondary monitoring system that rests on or within the product itself, called a temptale recorder. Temptales, like newer reefer units, also provide real-time information.


It is the receiver’s responsibility to pulp the product for acceptance or rejection. If a shipment pulps differently than the specified temperature range on the bill of lading, the burden of proof then points back to the driver’s equipment or the shipper. The final determination for freight rejection and claims depends on the documentation, including original specifications, sign-offs, and photos.



How to Pulp


To get the most accurate reading when pulping produce, use a pulp thermometer to pierce the skin of the product. Leave the probe inserted for three to four minutes to get the most precise reading. If the product is individually bagged, like salad greens, you obviously can’t pierce the bag, so fold the bag in half and place the probe in between the two sides. If you are using a digital thermometer, place it as close to fruit or vegetable as you can. To make sure your digital reading is correct, wait a few minutes and retake it in a nearby location for accuracy.


Mixed Loads and Temperature Specifications


Blue Book Services offers an invaluable guide, “Compatibility, Temperature Guidelines, and Ethylene Sensitivity,” for anyone shipping produce on refrigerated trucks. The three-page document groups produce into categories according to their compatibility in transit. Factors that affect fruit and vegetable viability are recommended temperatures (listed in the guide as in Fahrenheit and Celsius), relative humidity requirements, and ice contact acceptability.


Ethylene is used in some produce to quicken the ripening of certain fruits and vegetables. Temperature and humidity play a significant role in keeping ethylene in check. If the ethylene concentrations are too high, it can promote premature ripening, leading to food waste and freight claims. Vegetables that are ethylene-sensitive should never be shipped with produce that emits ethylene.


Shippers sometimes want to ship multiple products requiring different temperature specifications, such as frozen and fresh food on the same truck, as a cost saving measure. This type of shipment is considered ‘high risk’ and is not recommended for several reasons. Frozen is typically transported at 0 to -10 degrees Fahrenheit while fresh runs at 28-38 degrees Fahrenheit. That means the temperature on the reefer unit is normally set at 0 degrees for frozen with an allowance of up to -10 degrees. For fresh product, the reefer unit is normally set at 28 or 35 degrees, but the allowance is up to 38 to 43 degrees. These variances are specified to accommodate multiple drops for LTL shipments when the doors are opened and closed for separate deliveries. Additionally, just as there are different commodities that make up frozen and fresh shipments, the requested temperature settings can vary, as well as the acceptable ranges. 



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When attempting a multi-temp load, the shipper may request the unit set at 0 degrees for the entire trip, hoping that the fresh product will not freeze. Conversely, they may request a setpoint of 35 degrees, hoping that the frozen product will not thaw. On a multi-stop load, they may request a setpoint of frozen until the frozen product is delivered, then have the setting adjusted to a fresh setpoint for the remainder of the trip. Even with these temperature variances, there are no guarantees that the product will arrive on-temp. Temperatures affect different products in different ways, and some product (especially dry) emits heat, which can affect the product being transported with it.  One commodity can freeze at a certain temperature while another will not at that same temperature. Best practices are to keep your product safe, and not combine frozen, fresh or dry loads on the same truck.


There are specialized trailers (multi-temp trailers) that do provide mixed load services. These trailers have three separate temperature units in each zone of the truck, mounted on the ceiling.  But even with compartmentalized areas in the trailer, it is hard to completely control airflow in the rear of the truck, making it hard to ensure the safety of the varying cargo. Also, pallets cannot be stacked higher than six feet to allow proper airflow. That means less freight can go on the trailer.  Multi-temp trailers also are expensive, and the trucks are often difficult to find, so needing a next-day delivery can be a big challenge. Using a regular reefer trailer with bulkheads can also create problems. Bulkhead blockages can cause restricted airflow in other areas of the truck. Items closest to the bulkhead may freeze while temperatures in the back of the truck can become too warm.


How much is too much off-temperature?


That depends on several factors. Some perishable commodities are so sensitive to variations in temperature that if the trailer’s ambient air increases by two degrees, it can reduce the product shelf life by as much as 50% (Deltatrak).


Other causes of varying readings can be attributed to the location that the temperature was taken in the trailer or the recording device’s accuracy. Some of these discrepancies are allowed, even expected. A shipment that has multiple stops, for example, will likely experience more temperature variations than one that goes directly to the destination. It is important to differentiate when a temperature difference is tolerable versus when it puts the product at risk for spoilage. “Slight variations” usually fall into the realm of four to five degrees Fahrenheit, which may or may not be considered a breach of contract.


The amount of time the cargo is subject to being off temp can also be a factor. For frozen freight, several hours may not have any effect on the load, whereas the same amount of time for refrigerated freight will most likely wind up damaged and rejected. All produce shipments should be run at “continuous” regardless of the season. The start/stop/cycle causes too much fluctuation in the rise and fall of the ambient air temperature inside a trailer.


In the case of a claim, there is no one-size-fits-all for the rules regarding perishable freight. Shipments should be treated case-by-case depending on the type of temperature variation, the sensitivity and vulnerability of the product, and the due diligence of those responsible for upholding their duties according to the Food Safety Modernization Act, commonly known as FSMA.


To learn more, join our webinar, “Refrigerated Shipping: Myths versus Facts,” on August 20, 2020 at 2pm EDT. Click here for details.

Tags: Shipper News, Cold LTL, refrigerated freight services, frozen freight shipping, truckload freight shipping