Chefs know that, any way you slice it, wooden surfaces are kinder to knife blades than
either plastic or glass. But in recent years, everyone from kitchen suppers to the
Department of Agriculture (USDA) has urged cooks to cut on nonporous materials, typically
plastic. Supposedly plastic boards give bacteria, such as Salmonella in chicken, less
chance of escaping rigorous cleaning, thus reducing the chance that such bugs will survive
to contaminate Other foods.
If such arguments have frightened you away from slicing, dicing, or boning on wood, you
may be able to bring your butcher block out of retirement New research indicates that the
safety advocates were wrong: Pathogens prefer plastic.
No one was more surprised by this than Dean O. Cliver and Nese 0. Ak, two
microbiolgists at the University of Wisconsin-Madison. They began studying cutting boards
in hopes of identifying decontamination techniques that might render wood as safe as
plastic.
But the pair quickly found that within three minutes of inoculating wooden boards with
cultures of common food-poisoning agents - up to 10,000 cells of Salmonella, Listeria, or
Escherichia cali – 99.9 percent of the bacteria were unrecoverablc and presumed dead.
Under similar conditions, none of the bugs placed on plastic died.
Indeed, when the researchers maintained plastic boards overnight at high humidity and
room temperature, microbe populations grew; the researchers recovered no live bacteria
from wood the next morning.
The scientific literature suggests that the number of Salmonella cells that might wash
off a chicken carcass probably will not exceed about 1,000, Cliver notes. "We can get
less than 99.9 percent kills [on the wooden boards in three minutes] if we go to
inordinately high levels of inoculation" -such as l million or more bacterial cells,
he says. In those instances, he and Ak had to wait about two hours before achieving a 99 9
percent reduction in the bugs they recovered.
While the wooden boards appear to kill bacteria. "we've not recovered the
little critters' dead bodies." Cliver acknowledges. "So all we know is that
by the best available means, we can't get them back after they go onto a hoard." The
big concern is whether bacteria hiding deep within the wood might subsequently
surface to contaminate the foods an the chopping black "As best we can tell, that
isn't going to happen," Cliver says.
The same is not true of knife-scored plastic cuning boards. The scientists found
that bacteria lodged in the plastic's cut grooves not only survived a hot
watcr-and-soap wash, but could later surface to contaminate foods. By contrast, Cliver
says, with wood "a good wipe will do fine – and if you forget to wipe the
board, you probably won't be too bad off."
At one point, the Wisconsin researchers inoculated wood and plastic on three
successive days, maintatmng each board - without cleaning – at room temperatures and
high humidity By that time, "the plastic boards were downright
disgusting," Cliver says, "while the wood boards had about 99.9 percent fewer
bacteria than [Ak] had put on them."
"Wood is more forgiving -and perhaps user-friendly - than plasttc is once
it's been cut some," Cliver says.
Boards sold to homeowners typically come from the factory treated with mineral oil.
"That treatment is intended to make the wood more impermeable – like plastic,"
Cliver says. "The bad news is that it does make wood more like plastic....
In every one of our tests, if the wood had been treated to retard the
penetation moisture, the bacteria survived longer."
Wood's presumed bactericidal activity does not depend on whether it is new
nor, apparently, an species. Cliver and Ak have already tested bonds from hard maple,
birch, beech, black cherry, basswood, bunemut, and American black walnut. Tests on oak and
ash are pending.
The microbiologists hope to submit their findings for publication within the next few
months. One weakness, Cliver notes, is their inability to nail down a mechanism or agent
responsible for wood's antibacterial properties.
Although no laws prohibit commercial establishments from using wooden cutting boards,
the Food and Drug Administration's model code for state agencies call for using only
"nonabsorbent" and easily cleaned materials for surfaces that food contacts, The
USDA also recommends acrylic or other nonporous mxaterials to consumers asking about
preferred cutting boards, according to Bessie Berry with its Ment and Poultry Hotline in
Washington, D.C.
Cooks should never cut on glass, she says, because minute shards may chip off and
become embedded in food.
Microbiologist Priscilla Levine of USDA's Food Safety and Inspection Service says she
knows of no scientific studies demonstrating the advantages of one cutting-board material
over another in inhibiting bacterial contamination. She told SCIENCE NEWS that her
agency based its recommendations on "common sense.
Like state and local inspectors, these federal agencies have "bought the
myth" that plaslic is safer than wood, says food scientist O. Peter
Snyder, a St. Paul, Minn.based consultant to the retail-food industry For at least two
decades, he says, "sanitarians [sanitation inspectors] out there have been telling us
to use plastic cutting boards, even though they had no evidence that plastic was
better."
Indeed, Snyder contends, the little research done on the subject has failed to
demonstrate plastic's superiority He cited one study conducted about 25 years ago
that showed wooden cutting boards were at least as good as plastic when it comes to
cleaning off microbial contamination.
If others confirm the Wisconsin data, Snyder says, sanitarians may have to alter their
advocacy in favor of wood. But, he adds, considering how slowly practices change in
the food business, 10 years after such confirmatory data came in "sanitarians would
probably still be requiring [retail establishments) to use plastic cutting
boards."
