It was one month ago today that Colorado named its own “Rocky Ford-brand” cantaloupes as the likely source of a multistate outbreak of Listeria infection, which now could easily become the most deadly food poisoning in modern U.S. history.

With 112 sickened in 25 states and 23 mostly elderly Americans killed, the federal government’s report on its investigation into the cause of the Listeria contamination is said to be only a few days away.   

Jensen Farms, the grower that recalled at least 1.5 million “Rocky Ford-brand” cantaloupes two days after that first public health warning went out, and other Colorado cantaloupe growers are anxiously waiting for that report.

When the “root cause” — how deadly Listeria got into the cantaloupes — is identified by that report, it may then focus attention on harvest or post harvest practices and may even point to places where it is safer to grow cantaloupes than other places.

Specifically, it may be safer to grow “dry” cantaloupes in places like California than “wet” cantaloupes grown in more inland climes. Not even California cantaloupe growers have said that yet — although they come pretty close.

The distinction is whether cantaloupes are grown in such dry conditions that they can be field-packed, as is common in California, or whether they are grown where they need a bath before they are shipped, meaning they are shed-packed.   

Colorado’s major cantaloupe shippers, including Jensen Farms, do shed packing, according to Colorado State University’s Lawrence (Larry) Goodridge, a food microbiologist in the department of animal sciences. He says some small growers pack directly into bins in the fields.

While focused on Jensen Farms, the investigation by the U.S. Food and Drug Administration, federal Centers for Disease Control and Prevention, and state health agencies will bring attention to all cantaloupe growers in the Arkansas River Valley.

Most of those are wondering if and when they will be able to recover from having Rocky Ford cantaloupes associated with the deadly outbreak.

The findings will turn the spotlight on differences in the way cantaloupes and other melons are handled during and immediately after harvest. The one entity putting out a lot of information on this subject is the California Cantaloupe Advisory Board, which claims that California-grown cantaloupes have never been associated with a foodborne illness outbreak.

Jim Prevor, who writes about the produce industry as the “Perishable Pundit,” puts it this way:

“What the California cantaloupe industry found was that one should not wash a cantaloupe. That moisture itself is the enemy of safety. California packers, who were proud of their wash systems, shut them off.”

In four videos produced to educate both consumers and growers, the industry advisory board demonstrates both the field- and shed-packed methods of handling cantaloupes.  

While offering the opinion that either method can be safe if done right, field packing is depicted as both simple and safe. By contrast, shed packing comes across as complicated with all kinds of possibilities for cross contamination once equipment gets contaminated as it did at Jensen Farms.

The equipment used in shed packing can involve simple washes or sprays to clean cantaloupes before they are packed or they can involve more complete sorting and grading systems.   

Growers who do shed packing are not afraid to get melons wet, while growers who do field packing go out of their way to keep their melons dry.  

“A strong word of caution, however, in some cases using water on a melon contact surface meant to remove dirt can make things worse,” says one of the training films.  “In hard-to-clean, hard-to-reach places, water, melon juice and residues at warm air temperatures can combine to make a perfect breeding ground for bacteria.”

California cantaloupes are grown in neat rows keeping the melons above the irrigation water and keeping them clean and dry until field workers put them in a box and send them off to the cooler.

Colorado cantaloupes are harvested from the matted ground growth were they grew before they are collected and sent off for shed packing.

The question — no matter what the root cause turns out to be — is whether the harvest and post harvest practices made the contamination situation worse.    

By boxing in the field, California growers point out that if a melon was contaminated, it would cross-contaminate others in the same box. 

Packing sheds are complicated places. Melons are graded, sorted, sized, washed, cooled packed, and placed on pallets.  It is possible one cantaloupe going through shed packing might come into contact with dozens or even hundreds of others.

To come up with the root cause of the contamination, investigators will have to eliminate many other possibilities, Including domestic animals and wildlife feces, pest infestations, weather, melon rind surfaces, melon-to-ground contact, mechanical damage, melon wetting and brushing, and water quality of the cold water or topping ice used to cool melons.

While potential root causes are many, only one is getting much attention in the Colorado cantaloupe-growing area. A biosolids company that has sprayed fields in the vicinity is a Denver television station’s favorite suspect. The biosolids, which are used as fertilizers, originated with treated sewage from New York State.

This seems to be the one possible culprit that people know about. A woman who identified herself as Maxine called into Colorado Gov. John Hickenlooper’s monthly radio show, asking: “Are we going to continue to have sewage coming into our state and ruin the Rocky Ford cantaloupe business?”

Hickenlooper said while it is not known for certain yet, he doubts there was Listeria in the biosolids. He also agreed with growers in the immediate area around the town of Holly Ford that the Rocky Ford brand does not extend almost 100 miles to the east to include Jensen Farms.

But prior to the outbreak, there is no record of anyone objecting to Jensen Farms marketing its cantaloupes under the “Rocky Ford” brand.