DENVER -- Federal officials are expected to join state agricultural and state health officials in the San Luis Valley on Wednesday to inspect the food safety operation at a vegetable farm.

That move comes on the heels of another food recall following the discovery of E. coli bacteria in a package of salad from a store in Canada.

The voluntary recall affects all packages of Dole's Hearts Delight salad mix sold in the United States and Canada with a best-if-used-by date of Sept. 19, 2007, and a production code of A24924A or A24924B.

The Romaine, green leaf and butter lettuce hearts that went into the mix were grown in California, Ohio and in Colorado's San Luis Valley.

The salad mix was processed at a plant in Springfield, Ohio.

"We don't know where the contamination came from," said Sheldon Jones, Colorado's deputy commissioner of agriculture. "The FDA will join state health and agriculture inspectors in the San Luis Valley to inspect operations at the farm where the Colorado lettuce was grown. ... They'll check the fields, cooling shed and the packing house."

When asked if it was more likely that the contamination happened at a farm or at a processing plant, Jones responded, "The closer to the point of consumption, the higher the possibility that that's where the contamination took place."

On the outskirts of metro Denver, local farmers take numerous steps to ensure food safety.

At Petrocco Farms in Adams County, the focus is on both the product in the field and conditions in the packing house.

"We take food safety seriously," said David Petrocco, Jr. "Our name is on the (shipping) box."

Petrocco said he'd heard about the latest recall.

"It's concerning to us, because last year's spinach recall affected our sales even though it (the contaminated spinach) didn't come from Colorado at all," Petrocco said.

The Petrocco family has been growing vegetables south of Brighton since 1916. The owners stress food safety to all employees.

"Washing of hands, no eating in the fields. There are monthly random checks of (irrigation) water. There are monthly random checks of product," Petrocco said.

Inside the packing house, vegetables are quickly cooled with ozonized (purified) water.

"We produce about 30 tons of ice a day, which helps preserve the vegetables," Petrocco said. "We do our best to produce a safe product, and we're confident that we do that."

None of the produce grown at Petrocco Farms is used in prepackaged salads.

So Petrocco said, "When you take it home, it needs to be washed. You have to remember, it comes out of the ground."