Dean O. Cliver, Ph.D
We began our research comparing plastic and wooden cutting boards after the U.S. Department of Agriculture
told us they had no scientific evidence to support their recommendation that plastic, rather than wooden cutting
boards be used in home kitchens. Then and since, the U.S. Department of Agriculture’s Meat and Poultry
Inspection Manual (official regulations) and the U.S. Food and Drug Administration’s 1999 Food Code (recommended
regulations for restaurants and retail food sales in the various states of the U.S.) permit use of cutting
boards made of maple or similar close-grained hardwood. They do not specifically authorize acceptable plastic
materials, nor do they specify how plastic surfaces must be maintained.
Our research was first intended to develop means of disinfecting wooden cutting surfaces at home, so that they
would be almost as safe as plastics. Our safety concern was that bacteria such as Escherichia Coli O157:H7
and Salmonella, which might contaminate a work surface when raw meat was being prepared, ought not remain
on the surface to contaminate other foods that might be eaten without further cooking. We soon found that
disease bacteria such as these were not recoverable from wooden surfaces in a short time after they were applied,
unless very large numbers were used. New plastic surfaces allowed the bacteria to persist, but were easily
cleaned and disinfected. However, wooden boards that had been used and had many knife cuts acted almost
the same as new wood, where as plastic surfaces that were knife-scarred were impossible to clean and disinfect
manually, especially when food residues such as chicken fat were present. Scanning electron micrographs
revealed highly significant damage to plastic surfaces from knife cuts.
Although the bacteria that have disappeared from the wood surfaces are found alive inside the wood for some
time after application, they evidently do not multiply, and they gradually die. They can be detected only by splitting
or gouging the wood or by forcing water completely through from one surface to the other. If a sharp knife is
used to cut into the work surfaces after used plastic, or wood has been contaminated with bacteria and cleaned
manually, more bacteria are recovered from a used plastic surface than from a used wood surface.
“Manual cleaning” in our experiments has been done with a sponge, hot tap water, and liquid dish washing detergent.
Mechanical cleaning with a dish washing machine can be done successfully with plastic surfaces (even
if knife-scarred) and wooden boards especially made for this. Wooden boards , but not plastics, that are small
enough to fit into a microwave oven can be disinfected rapidly, but care must be used to prevent overheating.
Work surfaces that have been cleaned can be disinfected with bleach (sodium hypochlorite) solutions; this disinfection
is reliable only if cleaning has been done successfully.
The experiments described have been conducted with more than 10 species of hardwoods and with 4 plastic
polymers, as well as hard rubber. Because we found essentially no differences among the tested wood species,
not all combinations of bacteria and wood were tested, nor were all combinations of bacteria and plastics or
hard rubber. Bacteria tested, in addition to those named above, include Campylobacter jejuni, Listeria monocytogenes,
and Staphylococcus aureus. We believe that the experiments were designed to be properly representative
of conditions in a home kitchen. They may or may not be applicable to other plastic and wooden food
contact surfaces or to cutting boards in commercial food processing or foodservice operations, but we have
no reason to believe that they are not relevant, except that not all plastic surfaces are subject to knife-scarring.
Before our first studies had been published, they were criticized incorrectly for not having included used
(knife-scarred) cutting surfaces. We had been careful to include used surfaces, and so were surprised that
others who did later experiments and claimed to have refuted our findings often had used only new plastic and
wood. Although some established scientific laboratories say their results differ from ours, we have received
multiple communications form school children who have done science projects that have reached essentially the
same conclusions that we did.
We have no commercial relationship to any company making cutting boards or other food preparation utensils.
We have tested boards and cleaning and disinfection products, some of which were supplied to us gratis. We
have not tested all of the products that have been sent to us, simply because there is no time. We are aware
that there are other food preparation surfaces made of glass or of stainless steel; we have done very little with
these because they are quite destructive of the sharp cutting edges of knives, and therefore introduce another
class of hazard to the kitchen. We believe, on the basis of our published and to-be-published research,
that food can be prepared safely on wooden cutting surfaces and that plastic cutting surfaces present
some disadvantages that had been overlooked until we found them.
In addition to our laboratory research on this subject, we learned after arriving in California in June of 1995 that
a case-control study of sporadic salmonellosis had been done in this region and included cutting boards among
many risk factors assessed (Kass, P.H., et al., Disease determinates of sporadic salmonellosis in four northern
California counties: a case control study of older children and adults. Ann. Epidemiol. 2:683-696, 1992.). The
project had been conducted before our work began. It revealed that those using wooden cutting boards in their
home kitchens were less than half as likely as average to contract salmonellosis (odds ratio 0.42, 95% confidence
interval 0.22-0.81), those using synthetic (plastic or glass) cutting boards were about twice as likely as
average to contract salmonellosis (O.R. 1.99, C.I. 1.03-3.85); and the effect of cleaning the board regularly after
preparing meat on it was not statistically significant (O.R. 1.20, C.I. 0.54-2.68). We know of no similar research
that has been done anywhere, so we regard it as the best epidemiological evidence available to date that
wooden cutting boards are not a hazard to human health, but plastic cutting boards may be.
Publications to date from our work:
Ak, N.O., D. O. Cliver, and C.W. Kaspar; 1994. Cutting boards of plastic and wood contaminated experimentally
with bacteria. J. Food Protect. 57: 16-22.
Ak, N. O., D. O. Cliver, and C. W. Kaspar. 1994. Decontamination of plastic and wooden cutting boards for
kitchen use. J. Food Protect. 57: 23-30; 36.
Galluzzo, L., and D.O. Cliver. 1996. Cutting boards and bacteria--oak vs. Salmonella. Dairy, Food Environ. Sanit.
Park, P. K., and D. O. Cliver. 1996. Disinfection of household cutting boards with a microwave oven. J. Food.
Protect. 59: 1049-1054.
Park, P. K., and D. O. Cliver. 1997. Cutting boards up close. Food Quality 3 (Issue 22, June-July): 57-59.