Should bagged prewashed lettuce be washed again before eating?
To kill off bacteria, packagers of prewashed organic and conventional lettuce first rinse the greens with water and then typically spray them with a diluted chlorine solution. Despite these measures, E. coli outbreaks associated with prewashed bagged lettuce and spinach have been reported. Nonetheless, the U.S. Food and Drug Administration and many other food safety experts take the position that prewashed lettuce can be used without further washing. Here’s why: Prewashed produce is likely to have fewer bacteria (or none at all) than your kitchen sink or counter, and washing the greens may actually introduce bacteria. (We found this to be the case when we took swabs from prewashed lettuce straight from the bag and swabs from lettuce we “rewashed” in the test kitchen. The rewashed lettuce grew bacteria in a petri dish, while the untouched prewashed greens did not.) Furthermore, according to Trevor Suslow, a microbiologist specializing in food safety research at the University of California, Davis, if pathogens such as E. coli or Salmonella are actually present, rewashing removes very few cells and may actually spread contamination.
The bottom line: We agree with the experts who say additional washing of ready-to-eat greens is not likely to enhance safety.