I am asked from time to time to summarize the process of perishable shipping during the “ice age.” I usually reply that I have written several lengthy and, I think, complete posts on the subject, but am still asked for a “summary.” So this post is such a summary; a few connections to earlier ones are listed below. You can also use “perishables” as the search term in the search box at right.
I won’t identify all my previous posts about perishables here, but there are a few core ones, and here are some links to them. For example, see: https://modelingthesp.blogspot.com/2011/07/few-words-on-packing-houses-and-produce_25.html . For a more general consideration of perishable shipping, you might like this one: https://modelingthesp.blogspot.com/2021/12/reflections-on-ice-refrigeration.html .
Another issue is terminology. Of course you can use whatever terminology you like, but I always recommend that you simply use the prototype language that the railroad would have used. I’ve summarized this in a previous post (see it at: https://modelingthesp.blogspot.com/2012/12/refrigerator-car-service-terminology.html ).
Now to the concepts. Produce is harvested at a stage of ripeness that takes into account shipping time, from nearly ripe to well short of full ripeness. The produce from the field or orchard, after cleaning, sorting and culling out sub-standard pieces, needs to be chilled to shipping temperature. “Field heat,” comprising both heating due to warm air, and the heat of biological processes, needs to be removed so ripening falls to a very low rate.
Below is a packing house interior near Ventura, Calif., in 1928 (Keystone photo for Sunkist).
Before about World War II, most produce was simply loaded warm into the car, and then the subsequent initial icing was intended to cool the cargo en route to the first 24-hour interval icing. But after World War II, more and more packing houses began to pre-cool produce, which could much more rapidly reduce it to shipping temperature, improving quality.
For solid vegetables or fruit like the lemons above, such as melons, apples, celery, carrots, cauliflower, and so forth, hydro-cooling was effective. This meant cooling the produce in chilled running water for ten minutes or so. With leafy vegetables like lettuce, spinach or celery, vacuum pre-cooling was used. The produce was lightly sprayed with water, then subjected to an environment of reduced atmospheric pressure. This rapidly evaporated the water, taking with it the heat of evaporation.
With pre-cooling, the produce was already near shipping temperature, and could be loaded directly into a refrigerator car. Depending on the shipper’s choice, the car could have been pre-iced, meaning with ice in the bunkers when it arrived at the packing house, or if an un-iced but loaded car would go fairly directly to an ice deck, the initial icing before departure would be sufficient.
Below are men loading a PFE car with Bartlett pears (PFE photo, CSRM). Note that ice is visible in the end bunker, so this car has been pre-iced. Crates are stacked with spaces between; for air circulation.
One issue that is often misunderstood is the use of salt. The minimum temperature achievable, with a lot of salt, is around 10 degrees Fahrenheit, compared to 32 degrees with water ice only. Heavy salt like that was used for frozen food, and lesser amounts for meat, where the desirable shipping temperature was in the twenties of degrees. For produce, even less salt was used, to avoid sub-32-degree temperature, but it did give more rapid cooling, as the temperature would drop faster.
But this could actually be a problem, as was described in one of my interviews with Pete Holst, who was PFE’s Car Service manage for many years (see more: https://modelingthesp.blogspot.com/2012/09/pfe-operations-from-pete-holst.html ). Shippers of produce were ordering their pre-iced cars to receive salt also, increasing the switching needs. As Pete related it, he met with the shippers:
“So I went in there and I told ’em, ‘Now you fellows are just spending your money and losing it. You’re ordering these cars initially salted, and as soon as that salt hits the ice in there, that water starts pouring out. Then it gets to your shed, you open the doors, and it stands open for two hours while you load the car. You’ve used up half of your tank of ice, and you haven’t got any [cooling] use for it. If you’ll just load in a regular iced car, and say initial icing with two per cent salt, and bill it that way, then you’ll get the full refrigeration that you’re entitled to.’
“Well, they could see that they were just wasting their money, see. So I got ’em all to either decide on two per cent or three per cent [in initial icing] when they billed the car, then when it got to the ice deck we could take care of it. Salt was put in after the car was loaded, at initial icing. Then you really start doing a cooling job.”
When modelers have space to include an ice deck, it adds interest and additional car movement, whether at a big deck or a small one. Here’s an image I’ve always liked (Don Sims photo, El Centro Calif.), with two-man crews at each end of each car, filling ice bunkers, and on the ground, a clerk with a clipboard, chalking switching directions on the cars.
For more background on both icing and perishables, you could consult the PFE book (Pacific Fruit Express, 2nd Edition, Thompson, Church and Jones, Signature Press, 2000) — which also contains a chart of desired shipping temperatures for a wide variety of produce — that’s in addition to the blog posts cited at the top of this post. These provide in-depth background on how perishables were shipped in the era of ice refrigeration.
Tony Thompson
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