Cliver 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. Wooden cutting boards pulled 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 found that the bacteria never reappeared on the surface, even after it’s been sliced multiple times with a sharp blade.
Related: How To Care For A Wood Cutting Board
And while new plastic cutting boards can be cleaned and disinfected to the point where few bacteria remain, the same cannot be said for old knife-scarred boards.
“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 because the bacteria didn’t actually die—they were re-deposited on other surfaces in the dishwasher. And tests on old plastic boards treated with disinfectants such as chlorine bleach still found levels of residual bacteria hiding in grooves, he adds.
Similar research performed by the Hospitality Institute of Technology and Management 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.
After replicating Cliver's 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.”
Related: 11 Ways To Cut Food Waste In The Kitchen
After hearing from a microbiologist friend who microwaved his wood cutting boards once a week to kill residual bacteria, Cliver conducted a separate experiment to see if that did, in fact, kill bacteria, and it did, he says. The microwave even got to the bacteria deep beneath the surface. He recommends washing off food residue and then putting larger boards in for five minutes and smaller boards for two on a weekly basis. This trick doesn’t work for plastic boards, he says, because the material is so heat-resistant that it doesn’t get hot enough. Note that some wooden cutting boards are held together with metal strips, not glue, so they’re not microwave friendly. If you see sparks fly when you hit start, take the board out immediately.