Wednesday, July 13, 2011

A few words on packing houses and produce shipping-2

My previous post with this title was presented last month, and it briefly touched on what packing houses do, and on packing box labels. To view it, go to:
     Now I want to address issues of refrigeration for the produce shipments. As mentioned in the “Western Perishables” chapter of the book I co-authored, Pacific Fruit Express (A.W. Thompson, R.J. Church, and B.H.Jones, Signature Press, 2nd edition, 2000), there are considerable formalities to tariff and regulatory aspects of railroad refrigeration. But to summarize briefly, empty reefers were delivered to shippers either with ice already in the bunkers (called pre-icing) or without ice. Which one was specified by the shipper depended on the crop being shipped, and of course on the climate at that point in the harvest season. After loading, nearly all produce cars were iced (called initial icing) unless moving in ventilation service.
     Part of the decision on a shipper’s part about pre-icing was whether the produce could be cooled before loading (called pre-cooling). If the lading could be pre-cooled, then it was not usually necessary to order a pre-iced car, not only saving the icing cost but assuring the shipper better control of the shipping temperature of the cargo.
     The reason for the latter statement is that any produce needed to have the “field heat” removed. This heat was composed of both the obvious thermal heat, from sunshine and warm air, and also the biological heat from ongoing life processes in the fruit or vegetable, processes that did not stop immediately upon picking. Removing the field heat slowed or stopped ripening and assured that the produce would reach its destination in condition to be sold.
     Putting produce into a reefer direct from the field or orchard meant that field heat had to be removed during the first 24 to 30 hours of shipping, as ice melting gradually absorbed heat from the warm air rising from the cargo. This was speeded if the ice melt did not also have to absorb heat from a warm car body, thus the desire to pre-ice cars if there was a chance the empty car might be warm when delivered.
     Note the terminology, taken from the perishable tariffs: cargoes are pre-cooled, cars are pre-iced. Modelers sometimes mix the terms, but I prefer to rely on the terminology actually used in the period I’m modeling.
     Shippers might also choose ventilation service instead of refrigeration, in other words to have the ice hatches latched open so that surrounding air would blow through the car in transit. Obviously this would only be done if temperatures en route were expected to fall into the desired range.
     So what was pre-cooling? It might be nothing more than placing the packed produce in a cooled room overnight. For dense produce like melons or citrus or apples, dunking the produce in a stream of cold water before packing might suffice for pre-cooling. With leafy vegetables like spinach or lettuce, misting them with water and then subjecting them to a partial vacuum would provide greatly accelerated evaporation and thus cooling (called vacuum pre-cooling). The shipper, of course, chose what was feasible and economic for his particular crop.
     To sum up what is being described here, empty cars might be pre-iced (meaning they had to be set to an ice deck before spotting at the shipper’s loading dock), or not pre-iced, and then would normally be iced again on departure. Alternatively, they might move in vent service, with hatches latched open and no icing.
     En route to destination, cars were usually re-iced at intervals such as 24 hours (shippers could specify any interval they wanted). Often the 5000 pounds of ice in each ice bunker would be depleted by 1000 to 2000 pounds in 24 hours during normal summer transit weather. The bunker would be refilled and the shipper billed for the amount of ice used.
     Just to provide a model illustration, here’s a PFE reefer at the ice deck in my town of Shumala, with a flat car being picked up from the team track in the background. In this particular case, the car was being initial iced before departure.

In the background, you may notice the Giant Orange stand, and a billboard made from an actual cantaloupe box label.
     These refrigeration details are important on my layout, due to multiple packing sheds, and I’ve tried to make them consistent with real railroad practice.
Tony Thompson

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