People are eating more raw and organically grown fruits and vegetables these days. And that has many consumers concerned whether they are properly cleaning their produce. Michael Doyle, a professor of food microbiology at the University of Georgia and director of its Center for Food Safety, offers his opinion on how to wash fresh food—and whether it's OK to rub an apple on your shirt.

Harboring Enemies

When it comes to anything plucked from the produce aisle, Dr. Doyle says there are two main concerns—pesticides, which he doesn't worry much about, and microorganisms, which he does. "There have been lots of studies done by the government showing that pesticide contaminant tends to be at levels that are below health concerns," he says.

The more serious threat is microorganisms, especially salmonella, listeria and certain strains of E. coli. These sicken more consumers as a result of eating fruits and vegetables than eating meat or poultry, he says. The bacteria are sometimes spread through contaminated irrigation water and can settle on the surface of fresh produce, particularly those with layered leaves.

"Washing produce with tap water should help reduce residual pesticides and any dirt on the surface, where listeria and other bacteria often harbor," he says. But if harmful bacteria are present deep in the leafy greens that have been cut, "the extra washing you do at home isn't going to help," he says.

In the Bag

Even when bagged lettuce says it's been double washed, microorganisms that make their way into the water at the processing facility can spread onto whatever is being washed, Dr. Doyle says. Also, once the lettuce or spinach has been cut, surface microbes can become entrapped within the leaf itself. "When that happens, there is no washing it out, no matter what you do," says Dr. Doyle. "This may be one reason why bag salads and cut greens have been some of the biggest culprits in spreading foodborne illnesses recently."