What is the best food-safe finish?
I make a lot of cutting boards and typically apply an edible oil, such as pure tung oil or food-grade mineral oil, to enhance the appearance of the wood and protect it. Are there other oils, waxes, or film-forming finishes that would offer more protection and still be food-safe?
—Chuck Wagner, Raleigh, N.C.
As you've discovered, Chuck, any natural oil that won't go rancid works fine, including walnut, linseed (not the "boiled" variety), or extra virgin olive oil. Although mineral oil is derived from petroleum, the food-grade version proves popular because it's colorless, odorless, flavorless, and inexpensive. Such oils beautify the wood and offer some resistance to liquid penetration but need to be reapplied regularly.
A film-forming finish, such as polyurethane, provides maximum protection and proves safe for food contact after complete curing—a process that can take several weeks. But it's not suitable for cutting boards, salad bowls, or other surfaces that come into contact with knives and other hard utensils. Moisture and bacteria will penetrate any cuts and get trapped under the finish. With that said, if a film-forming finish suits your needs but you want to avoid any chance of ingesting plastic, try shellac. Made from a natural secretion of the lac bug mixed with alcohol, shellac even finds its way into pharmaceuticals. Just don't let it contact alcohol, which will dissolve it.
To increase the water resistance of edible oils, try mixing them with beeswax. Simply mix small chunks of wax into heated mineral oil (about 1 part beeswax to 5 parts oil) to make a highly effective, food-safe finish. To avoid a fire hazard, just be sure to heat the oil in a container placed in boiling water.
On today's market you'll find many pre-mixed, food-safe products, most containing the edible oils mentioned earlier. Some include wax, too, saving you the heating/mixing work.
No matter which product you choose, before applying it thoroughly clean the cutting board with soap and water. Never wash the cutting board in a dishwasher or allow it to soak in water—the board may delaminate or warp. After allowing the board to dry, apply the oil or oil/wax blend and let it soak into the wood for several hours before wiping off any excess.