SmartAir Offers In-Transit Banana Ripening

Aug. 1, 2001
Almost more than any other fruit, bananas fill a long pipeline, one that runs from plantations in Central America, Caribbean islands, or Africa to markets

Almost more than any other fruit, bananas fill a long pipeline, one that runs from plantations in Central America, Caribbean islands, or Africa to markets throughout the world. Movement through this supply chain must be precise to present fruit to consumers table-ready while maintaining maximum shelf life for wholesalers and retailers.

Bananas are an impulse purchase, says Bob Blinstrub, a former official of Trans Tech Holdings Group. If fruit is the appropriate color and unblemished, shoppers will buy. If bananas are still green, shoppers keep walking, he says.

To ensure a supply of properly ripened fruit, supermarket chains and wholesale grocers invest large sums and valuable distribution center space to banana ripening rooms. These are rather like a bulge in the pipeline, where fruit slows down for four to five days on its way to market. Taking the ripening room bulge out of the banana pipeline is the goal of SmartAir® technology, which was originally proposed by Trans Tech Holdings. SmartAir and an associated technology known as TransRipe® have been developed for commercial applications by Carrier Transicold. Blinstrub has been retained by Carrier Transicold to help integrate SmartAir technology throughout its product line.

Transport in Bulk or Container

Bananas move from plantation to market in two ways. In North America, about half of total banana shipments move in refrigerated marine containers. The remainder is shipped as palletized loads in bulk refrigerated vessels. In both instances, additional transportation is required from the port to points of inland distribution. At times, this is a seamless move with containers traveling by highway directly from the ship to the wholesaler. At other times, containers are off-loaded and unstuffed at the port and the fruit shipped in conventional highway trailers.

The choice of transportation modes depends on the wholesaler's distance from the port and the availability of container-compatible freight in the destination area. Marine containers are difficult to use in some areas, because of the combined weight of the container and its highway chassis, because they offer less cargo space than a high-cube highway trailer, and because they must be returned to the port within a specified time window. The best procedure for returning containers to a port is shipping merchandise from an inland point of origin to an overseas destination. If enough time is available, some carriers use containers to move domestic freight to receivers near the port. The worst-case scenario involves an empty container move from the banana receiver to the port.

The cycle from harvest to sale for bananas is relatively long. Fruit may be harvested as much as six days before sailing from the country of origin. The ocean voyage from Central America to ports on the Gulf of Mexico can take up to three to six days or more to ports such as Wilmington, Delaware. At a distribution center, bananas can be held for several days before they are prepared for retail sale, Blinstrub says. However, once a wholesaler has ripened the fruit, it must be distributed and sold quickly. Although bananas with many brown spots on the skin are great to eat, consumers tend to buy fruit that is deep yellow in color, he says.

Ripening bananas during highway transportation offers multiple advantages to wholesalers, says Tom Ondo, director of marketing and product development for Carrier Transicold. It reduces the total amount of fruit in inventory, cutting purchase and storage costs, and allows rapid cross-dock handling. In addition, mobile ripening has the potential to allow the building of new distribution centers without the expense of installing ripening rooms.

Distributors can benefit in two ways from receiving fruit already in condition to sell, Blinstrub says. The most obvious is better use of scarce distribution center space that would otherwise be required for ripening rooms. The other is safer storage of the entire produce line. Banana ripening requires the use of ethylene in the process. Some produce is adversely affected by contact with ethylene. For instance, cut flowers wilt almost immediately in the presence of ethylene. Operating a produce warehouse without the presence of ethylene results in reduced potential for contamination of ethylene-sensitive products throughout the building.

In-transit ripening requires equipment that offers two major differences from conventional highway trailers and refrigeration units. Just the same as stationary ripening rooms, a mobile ripening system must have precise temperature control and a pressurized air handling system to force air and ethylene gas into every cavity around boxed fruit.

200 Units in Service

Ripening fruit on the highway has progressed beyond the concept stage. Roughly 200 trailers with SmartAir technology are already in service. The equipment, involving a highly modified trailer and refrigeration unit, costs between $65,000 and $75,000, depending on final system configuration. “Although this is a premium over conventional reefers, the additional fruit processing capabilities offered by SmartAir provides the potential for excellent return on investment to the user,” Ondo says.

As produced by Carrier Transicold, a SmartAir unit is based on the Ultra/Ultima refrigeration unit platform. The refrigeration unit has an additional 5-kilowatt generator taken from the Genesis series of multi-temperature systems. The generator provides 230 vac current to power four fan pods and an ethylene gas generator installed behind a 16-inch deep bulkhead that forms an air mixing chamber at the front of the trailer interior. Each of the fan pods has two blowers. Two pods are installed at each side of the front bulkhead. The four blowers in two fan pods are capable of moving more than 10,000 cubic feet of air per minute. The fans are controlled by a SmartAir control box mounted at the front of the trailer. In addition, the control box operates the ethylene gas generator and the fresh air exchange system used to vent gas from the trailer after the gassing cycle is complete. Although the refrigeration unit has a start/stop controller, the unit runs continuously when the SmartAir system is in use.

Discharge air from the refrigeration unit evaporator empties into the mixing chamber behind the front bulkhead. The discharge mixes with air in the trailer for precise temperature control, typically within ±1° F at any point in the trailer. Most of the mixed air is captured by the fan pods and directed down the trailer sidewalls instead of flowing above the load as it would in a conventional refrigerated trailer.

Ethylene Boosts Ripening

Ethylene gas is a normal by-product of banana respiration given off as the fruit ripens. In the controlled ripening process, fresh air is excluded from the trailer and fruit temperature is increased slightly from the transit temperature of 56° to 58° F, and ethylene gas is introduced at a concentration of roughly 150 parts per million to accelerate normal ripening. The gas generator is filled with liquid ethylene, which vaporizes when dripped onto a heated surface. When the controlled gassing cycle is complete, temperature is reduced again, and the trailer is continuously flushed with fresh air to prevent the fruit from maturing further. The ripening cycle is controlled by a timer in the SmartAir control box.

Just as stationary ripening facilities are specially built, trailers for mobile ripening must be built to custom specifications. These include the false wall at the trailer nose for installation of the fan pods and ethylene gas generator, a curb along each sidewall just above the floor to prevent air movement through the pallets that banana cartons are stacked on, and air delivery ducts with downward-facing outlets along the upper sidewalls that produce a pressurized plenum. When trailers are loaded with pallets placed firmly against the lower curb and upper delivery duct, banana cartons form the inner wall of a floor-to-ceiling air plenum approximately two inches deep. The rear of the plenum on each side is sealed by a movable pressure bar. Trailers are loaded with a void or aisle down the middle for air return to the refrigeration unit. The fan pods force air through the ducts, pressurizing the plenum. A pressure differential of 2.3 to 2.6 atmospheres between the plenum and the air return aisle pulls a high volume of temperature-controlled air through the stacks of product. The result is that SmartAir actually controls product temperature instead of simply surrounding the product with a blanket of cool air.

Loading Controls Airflow

Proper trailer loading is critical to the functioning of the SmartAir system. Pallets must be snug against the walls, and a return aisle must remain down the center of the trailer. If either of these conditions is not met, pressurized air cannot be forced through the cartons. With proper loading, airflow through a typical pallet load can be as high as 500 cubic feet per minute. An average carton contains 16 hands of bananas.

Floor drains on SmartAir trailers are equipped with valves. Carrier Transicold recommends closing the drains during transit so that evaporator defrost water will collect on the trailer floor, raising humidity in the trailer. Opening the valves drains defrost water from the trailer.

SmartAir technology can do more than ripen bananas, says Jan Parker, Carrier Transicold's special applications product manager. By forcing cold air through produce cartons, the system can eliminate the need for stationary precooling systems in the produce supply chain. For the first time, the transportation industry has the capability to remove field heat from produce in transit, she says. Potentially, expensive hydro cooling or vacuum cooling systems for fresh produce would no longer be needed, she says.

The SmartAir system is commercially available through Carrier Transicold's national accounts group. It is a build-to-order product with service, parts, and warranty support available through Carrier's dealer network, Ondo says.

About the Author

Gary Macklin

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