Tomato scare shows complexity of supply chains

Fresh tomatoes at the market pass through many hands before we sink our teeth into them.

Most of the time we can bite with the confidence that they're not going to make us sick. But, as the salmonella outbreak shows, the food safety system isn't fail-safe. Harmful bacteria can colonize a tomato at many points on the path from vine to salad bowl.

The strategies used to keep those bugs out of your belly differ depending on how and where a tomato is grown. Here are five common varieties found in late spring and summer.

-- Mexican red Roma, red plum and red round: These types of tomatoes are the likely culprits in the nationwide outbreak -- but, of course, they're not all bad.

Tomatoes of this sort generally are picked just as they're beginning to turn from green to red. They're usually washed in a warm bath of chlorinated water, and then ripen on their way to market. The warm Mexican climate allows farms to supply a large share of the U.S. tomato market in the winter and spring.

Contamination of fresh tomatoes with polluted water is a big concern on Mexican farms, said Trevor Suslow, a produce safety expert at the University of California, Davis. In order to keep their lucrative U.S. contracts, many farms have gone to great lengths to keep their tomatoes safe, including installing water-treatment plants to provide clean water for irrigation and washing.

Supermarkets that sell field-grown Mexican tomatoes generally have elaborate food-safety contracts with suppliers. These agreements are meant to ensure compliance with a host of guidelines, including testing of soil and water quality and hygiene requirements for workers.

-- Hothouse tomatoes (often sold with the vine attached): These are grown indoors along the West Coast from British Columbia to Mexico. They are typically picked ripe, and then, without being washed, are immediately put into plastic containers labeled with codes that allow tracking all the way to the store shelf, according to Jim Gorny, who directs the Postharvest Center at UC Davis.

Growing tomatoes indoors where the fruit likely won't touch soil or water keeps the risk of food-borne illness low, though contamination during handling is always a possibility.

-- Heirloom and other farmers market tomatoes: Several local farmers who sell tomatoes direct to consumers said their main food-safety priority is to make sure that pickers keep their hands clean. Farmer's market varieties are grown on trellises and drip-irrigated so the tomatoes generally don't come into contact with soil or water.

Thaddeus Barsotti, who runs Capay Organic in Yolo County, Calif., and grows about 250,000 pounds of heirloom tomatoes a year, said his tomatoes are too fragile to be washed after harvest. They're packed in low boxes and then delivered, generally within a day. Barsotti encourages his customers to wash tomatoes at home.

-- Standard supermarket tomatoes (the common red varieties sold without stems in supermarkets around the country in summer): These tomatoes grow on low, bushy plants that don't require trellises. They are picked while still green and hard, washed in warm chlorinated water, sorted, and then shipped to ripening depots around the country. There, ethylene gas -- a natural ripening agent -- drives the tomatoes to turn red.

The mingling of mature green tomatoes from multiple farms during ripening can make it difficult to trace an outbreak of foodborne illness back to an individual farm, Gorny said.

-- Finally, there are backyard tomatoes, which grow wonderfully in the summer. Potential sources of contamination include dirty hands, manure used for fertilizer, and dog poop.

(E-mail Jim Downing at jdowning(at)sacbee.com. For more stories visit scrippsnews.com)