Research indicates that wood is a safer material in contact
with foodstuffs than currently recommended alternatives. For several months now,
I have noticed comments appearing in the woodworking press regarding the
comparative safety of wooden domestic-ware, or treen, paticularly when compared
with utensils produced from other materials. It seems to be a commonly-held
belief that synthetic surfaces and materials such as stainless steel and plastic
are intrinsically 'cleaner and safer' then those of natural materials such as
wood. Indeed, the EU is very specific on this and its regulations on food
hygiene specifically prohibit the use of wooden work-surfaces in areas where
food is produced for public consumption.
This ruling is vigorously upheld in the UK and supported by
national statute; happily, it seems that out EU neighbours have the sense to
apply this ruling somewhat more liberally, to their advantage. Why would I
endorse this 'lawlessness (!)'?. Simply because I believe in - and remembered -
the analytical work performed at the University of Wisconsin-Madison, USA, a few
years ago by Dr. Dean Cliver, at that time working for the Food Research
Institute. An abstract of the work was published in the UK at the time, but the
recent correspondence leads me to think that most woodworkers have forgotten
about it. My view is that the work is far too significant to those of us who are
potentially involved in producing wooden utensils such as bowls, cutting boards,
platters etc. for it to be forgotten and I therefore attempted to contact Dr.
Cliver with a view to re-publishing the information here.
Thanks to the prompt action of Tim Paustian at the
University of Wisconsin, who got me in contact with Dr. Cliver, now working at
the University of California, and of course to Dean Cliver himself, I have been
able to track down the information I was seeking on your behalf. The following
article was prepared by Dr. Cliver to summarise his work, and that of his
associates, on the safety of plastic and wooden cutting boards. My thanks to Dr.
Cliver for his help in making this information available to enhance our
understanding. I hope that you find it as interesting as I did - and that you
will now feel fully confident in defending the safety of wood against the modern
'alternatives'.
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 1995 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 authorise 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, so that they would be almost as safe as
plastics. Our safety concern was that bacteria such as Escherichia coli O157:H7
(commonly known as E-coli) 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, whereas plastic surfaces that were
knife-scarred were impossible to clean and disinfect manually, especially when
food residues such as chicken fat were present. Although the bacteria that had
disappeared from the wood surfaces were 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
dishwashing detergent. Mechanical cleaning with a dishwashing 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 disinfecting 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 food service 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
criticised 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 from school children who have done science projects that
have reached essentially the same conclusions that we did. We have no commercial
relationships to any company making cutting boards or other food preparation
utensils. We have tested boards and cleaning and disinfecting 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 not 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 determinants 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. 16:290-293.
Park, P. K., and D. O. Cliver. 1996. Disinfection of
household cutting boards with a microwave oven. J. Food. Protect.
59:1049-1054.
Others are in press or in preparation.
Dean O. Cliver, Ph.D.,
Professor, Department of
Population Health and Reproduction
School of Veterinary Medicine University
of California
My personal thanks go to Dr. Cliver for making
the foregoing material available to this website.
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