On the Chopping Block
Bad news arrived with an outspoken dinner guest. "You're carving on that?" she asked, pointing at the wooden board upon which the newly roasted duck awaited the knife. Well, yes, I was. We'd used that board for years, as had a great-aunt before us; it showed its age, so it did not leave the kitchen, but it was kindly to knives and comforting in its family tradition.
The upset guest told me she'd just read an article on how unsanitary wooden kitchen implements were. A butcher block might look elegant, but it was unhealthy, as were bread boards and meat planks of the sort I cherished. "Think of all those pores and nicks," she continued. "It makes sense that germs would thrive on wood. You never can get it really clean."
It did make sense. Soon I too saw articles exhorting cooks to avoid porous, organic, and germ-encouraging wood in favor of inert sterilizable plastic. Sadly I replaced my cherished wooden things with inorganic, impervious plastic, stuff so hostile to bacteria that nothing seems to cause it to decay.
Science giveth bad news, but sometimes it taketh away again. Recently, researchers at the University of Wisconsin-Madison have concluded that wood is good---and plastic is unhealthy.
Microbiologists Dean Cliver and Nese Ak were looking for ways to clean wood safely after it had been in contact with food contaminated by bacteria. The first step was to be sure their study boards had appropriately unpleasant microorganisms to be cleaned off. They cultured some known disease-causing bacteria, such as Salmonella, Listeria, and Escherichia coli, and anointed wooden boards with about 10,000 cells of cultured bacteria. That's about 10 times the number of organisms that typically wash off a contaminated chicken carcass.
Within three minutes, 99.9 percent of the bacteria were unrecoverable and presumed dead. By the next morning, the researchers couldn't recover any live bacteria from the wood.
Next, the scientists upped the germ count, inoculating the boards with a million or more bacteria apiece. Then they had enough survivors to work with, but not for long. Within two hours, again 99.9 percent of the bacteria had vanished.
Cliver and Ak tried the same procedures with plastic cutting boards. All the bacteria survived. The organisms even lived through hot water and soap washings in good health and high enough numbers to contaminate clean meat later placed on the plastic.
The scientist tried inoculating wood and plastic boards with bacteria on three successive days, and not cleaning the boards between inoculations. They maintained the boards under identical conditions of warmth and high humidity, comparable to a busy restaurant kitchen. At the end of the three days, once more 99.9 percent of the bacteria had vanished from the wood boards. The plastic boards were thriving germ farms.
The researchers have no idea what makes wood inhospitable to bacterial growth and survival. They aren't even sure that the bacteria are dying. According to the Science News article reporting their work, Cliver admitted "we've not recovered the little critters' dead bodies." But if the germs are hiding somewhere in the wood, nothing seems to lure them back out again.
The mysterious natural antibiotic effect of wood on food contaminating bacteria seems to work with old wood as well as new, and with every species of wood tested so far. The only thing they've found that does enhance bacteria growth is treating the wood with mineral oil. By sealing the wood, oiling makes it more like plastic. As far as bacteria are concerned, that's a good thing.
So great-aunt's board is set for use again, old, unoiled, and even barely washed. As Cliver explained, for cleaning wood, "a good wipe will do fine---and if you forget to wipe the board, you probably won't be too bad off.
