Dean O. Cliver, PhD, professor emeritus of food safety at the University of California, Davis, has been studying the issue since the late 90s. Recently he and a group of students cultivated Salmonella bacteria on new and used plastic and wood cutting boards and then cleaned them manually (with hot soapy water and a dish rag). Cliver and colleagues found that wooden cutting boards seemed to pull the bacteria down beneath the surface of the cutting board, where they didn’t multiply and eventually died off. Even older wooden cutting boards with deep grooves had low levels of recoverable bacteria, similar to what was found in new boards. “It’s been suggested that bacteria being slurped down in wood could reappear if you scored the wood with a knife,” says Cliver. But his research has found that the bacteria never reappear on the surface, even after it’s been sliced with a sharp blade.
And while new plastic cutting boards can be cleaned and disinfected to the point where few bacteria remain, the same can’t be said for old knife-scarred boards, Cliver found. “With the plastic, after manual washing as I would do under my kitchen faucet, we could still recover bacteria from grooves,” he says. Dishwashers didn’t eliminate the problem either: the bacteria didn’t actually die, they were re-deposited on other surfaces in the dishwasher. And, he adds, tests on old plastic boards treated with disinfectants such as chlorine bleach still found levels of residual bacteria hiding in grooves. Similar research performed by the Hospitality Institute of Technology and Management has found that unless plastic cutting boards are soaked nightly in bleach, they are very prone to absorbing hard-to-remove food residues that could promote the growth of bacteria and black mold.
Go with wood. Cliver’s experiments have been questioned by government scientists, but after replicating his research, both the USDA and the FDA have changed their food prep recommendations to include cutting boards made of maple or other hardwood surfaces. Just remember that any good you gain from using wood is completely negated if you don’t clean the board, says Cliver. “Don’t let food residues dry on the surface,” he says. “When I use wood, I clean it promptly.”