Cutting Board Finishes

Wooden cutting boards and butcher-block counter tops are hard-working surfaces, subjected to a daily onslaught of food products, liquids, sharp cutlery, and repetitive cleaning with soap and water. They need a protective coating that keeps food from entering the wood pores and makes the wood surface easier to clean, while enhancing the appearance. This coating must stand up to routine washing and be easy to maintain and restore.

There are several finishing and maintenance treatments commonly used for cutting board, and one that is often overlooked yet effective: vegetable oil.

Your choice of finish may depend on whether it is a new cutting board or whether you are maintaining one that has been used. If you are the woodworker making the board, you are probably aware of, and able to get, any finishing products you want. The end user might not have access to all of those options.

Also, the maker's priorities may differ from those of the end user. To attract a buyer, a new board must look good, feel good, and probably smell good. As the board acquires the patina of use and wear and multiple washings, the user's main finishing objective will be maintenance -- to refresh the protective coating and re-saturate the surface appearance. Above all, maintenance finishes should be convenient. This is where veggie oil excels. Every household has a ready supply of veggie oil on hand.

Four Cutting Board Finishes

The wood is soaked in mineral oil, USP or food-grade, available from the drug store. Some heat the oil while others heat the wood to aid penetration. The treatment is quick and cheap, and it looks good for items to be sold. The board may feel oily after treatment and oil may bleed out of the wood for some time. This treatment is the least durable.

Paraffin wax is dissolved in hot mineral oil and the resulting solution is applied to the board. The mineral oil aids penetration of the wax. This treatment is durable but more involved.

Some oils dry to a protective film upon exposure to oxygen. Walnut oil is the drying oil most commonly used for cutting boards, but other nut oils fall into this category, too. The wood is treated as it would be with linseed oil: wipe it on, then wipe the excess off. Related to this treatment is to coat with a wiping varnish (e.g., Waterlox), although some people worry about the presence of chemical driers in these finishes. It is unclear whether a wiping varnish will adhere to a used cutting board that has been exposed to oily or fatty foods.

Common vegetable oil is both handy and durable, and hence ideally suited for maintenance of cutting boards and butcher block counter tops. It is applied like walnut oil: wipe it on, then wipe the excess off. Repeat when the board appears dry. These oils are more viscous than mineral oil, and depending on the plant source, they can cure more or less quickly to become even more viscous or even form a durable film. They stick to the wood better than mineral oil. Another advantage is that every kitchen has some on hand to be reapplied as needed.

This treatment is controversial because some object to cooking oil going rancid. This concern is irrelevant for a cutting board or counter top that is going to be used to knead bread, cut up meats, or other activities involving food that contains fats and oils. In use, the board is going to pick up some amount of vegetable oil and animal fat which will simply add to the cooking oil previously applied to the board. The chemistry of producing rancid odors is identical to the curing of linseed oil and walnut oil, and no harmful products are generated. (See SIDEBAR: The Chemistry of Cutting Board Treatments) The odors result from the same volatile organic acids and related compounds that provide flavor and odor to fermented and cultured products like cheese and bread. A used wood cutting board is going to smell like a used cutting board no matter the finish used to pre-treat it. If the faint odor of a used wood cutting board is unacceptable, it would be better to use a plastic cutting board and run it through the dishwasher.

In summary, cooking oil is a handy and effective means of treating a cutting board with a durable, protective film.

Comments and Follow-Up Discussion

Keith Newton: My question is what to do before and after butchering meat. And, while the dense even texture of Hard Maple is desirable, is there any advantage to using woods with natural decay and insect resistance. Are these chemical-based properties bound to the wood, or subject to dissolving and being absorbed into the food?

Bill Tindall: After butchering, we wash the board or counter top with soap and water, a squirt of cleaner that contains bleach, and then a light renewal of veggie oil. After bread kneading, we just scrape the counter top blocks. The blocks we use for light-duty cutting of vegetables and the like get a wet wipe and renewal with veggie oil as needed. I am not paranoid about bacteria, as we live on a farm with sheep poop everywhere. In a commercial or public situation, though, people with immune issues have to be accommodated, which probably involves further routine disinfecting of cutting board surfaces. Regarding chemicals in the wood, heartwood is laden with chemicals to defend against fungus; I don't know about bacteria or whether these chemicals can leach into food. Good subject for further inquiry.

Ellis Walentine: I wonder about the difference between straight mineral oil and the mineral oil/paraffin mixture. I've been using Clapham's Salad Bowl finish for many years, which is an aqueous emulsion of (I think) mineral oil and beeswax. It gives an attractive, in-the-wood surface to cutting boards and salad bowls. It leaves a less oily feel to the surface and eventually seems to dry.

David Yoho: All cutting boards I make get one treatment and it has worked: Waterlox! I got this method from Charles Neil several years ago. The idea is not to create a surface film but one inside the wood that seals the pores.

Bill Tindall: We need to know about "driers". Driers are chemicals added to curing finishes (including varnishes like Waterlox) that speed their reaction with oxygen resulting in the smaller oil molecules adding together to make a huge molecule that we call a polymer, which becomes a tough and durable film. Waterlox or any vanish is going to initially be a better barrier than any alternative. How practical it is for maintaining a cutting board, I don't know.

Ellis Walentine: I have also used both Waterlox and Behlen's Salad Bowl finish on woodenware, as well as a product from Swing Paints called Antique Gel Varnish, which I have also found to have tougher resins that stand up well to normal use. The key with all of these is to wipe off the excess and let the remainder dry in the wood.

Bill Tindall: I don't see that hardness of the coating is relevant unless it sits on the surface. On the surface it will be cut in use and pieces flake off. In the pores a rubbery material would seem to be as effective as a hard one. Abrasion resistance would be determined by the wood and extraction resistance determined by properties other than hardness. In any case none of these formulated finishes is as convenient as adding a dab or veggie oil when needed.

Larry Clinton: Last board I made was coated with Walnut oil - several coats - wiped after each coat. I gave this to one of my son's along with the remainder of a bottle of the oil. Most of my boards have been coated with a hot mixture of beeswax and paraffin, with just enough mineral oil mixed in to soften the waxes. I have an old steam iron in my shop, used to lift dings, soften hide glue etc. When I heated the wax mix, I just turned the iron upside down, clamped the handle in my vice and set the pan on the iron - worked great. Then I applied the hot mixture onto the boards and "ironed" it into the boards, wiping the excess off while still hot. This seemed to penetrate very well and I've had one board in my kitchen for over five years old that still looks good.

I do know that some of the vegetable oils do become quite hard and solvent resistant. My youngest son works for a Soybean processing facility. A few years ago they removed and scrapped all their indoor and outdoor explosion proof lights and replaced them with new high efficiency units. My son asked and received permission to take the scrapped lights. I have a couple to install in the shop yet. The glass globe on these have been coated over the years with soy oil and this has hardened to an amber colored "epoxy" type coating harder than any enamel or varnish I have seen. I have tried to remove this mechanically, and with several solvents with little effect!

Bill Tindall: There is good chemical reason to suspect that eventually soy should make a solid film because is has some (but not as much) of the triglyceride that enables linseed oil to relatively quickly react with oxygen to make a coating. This triglyceride has more carbon atoms deficient in hydrogen that will react with oxygen to set off the chain of events that results in a tough film. In chemistry, more usually means faster, maybe a lot faster.

Clint Searl: Conventional wisdom seems to be roughly split between using a drying oil or a mineral oil concoction, with a resin based finish a distant third. Perhaps it's a moot issue, since there's no evidence that any offer a functional advantage over simply leaving the wood untreated.

SIDEBAR: The Chemistry of Cutting Board Treatments

This chemistry section provides more details about the chemistry of fats and oils and how they compare to the mineral oil treatment.

Mineral oil and paraffin wax are products of refining petroleum. They belong to a class of chemicals called "hydrocarbons." Cooking oil, vegetable oil, walnut oil and fats belong to a class of chemicals called "triglycerides." These chemicals are used by plants and animals to store energy. Animals store triglycerides that we call "fat" to get the animal through hard times when conditions are rough or nourishment is scarce. Plants store triglycerides, which we call "oils," in their seeds, to provide energy for germination.

Hydrocarbons are composed of only carbon and hydrogen. In general, for each carbon atom in the molecule there are two hydrogen atoms. That is, the ratio of carbon atoms to hydrogen atoms is 1:2, except at the ends of the molecule, a detail we can ignore for this discussion. The simplest and smallest hydrocarbon is methane with one carbon. Next is ethane with two carbons, propane with three carbons, and butane with four carbons. Naphtha is a mixture of hydrocarbon molecules that are made up of five to seven carbons, mineral spirits is a mixture of 7-12 carbon-containing molecules, mineral oil is a mixture of molecules that contain about 15 to 20 carbons, paraffin wax is a mixture containing more than 20 carbon atoms per molecule and polyethylene molecules contain up to 50,000 carbon atoms, more or less. As the hydrocarbon molecule contains more carbon and hydrogen the material becomes less volatile, beginning with methane, which is a gas, mineral spirits, which is a liquid, paraffin wax, which is a solid, and, finally, polyethylene, a special class of solids with special properties that we call a polymer.

Hydrocarbons are not affected by exposure to air or moderate heat. When mineral oil or paraffin wax is added to a cutting board it remains unaltered over time. These materials are essentially tasteless, odorless and colorless, and they will remain so upon exposure to air, unlike the plant oils.

Plant oils and animal fats are natural products that chemists call triglycerides. The name is derived from the fact that the triglyceride molecule contains three (tri) organic acid molecules attached to a glycerin molecule (glyceride). The organic acids are made up of carbon and hydrogen just like hydrocarbons but they also have carbon, hydrogen and oxygen at one end of the molecule that makes them acidic. We are familiar with many organic acids: formic (one carbon), acetic (two carbons), butyric acid (four carbons), and stearic acid (18 carbons). The acids in triglycerides typically contain 16 and/or 18 carbon atoms. These acids are collectively referred to as "fatty acids."

The acids that make triglycerides usually have some carbon atoms that are deficient in hydrogen, that is, the ratio of carbon atoms to hydrogen atoms in a fatty acid is typically less than 1:2, unlike the case for a hydrocarbon. These deficient carbon atoms will react with oxygen when exposed to air. When they react with oxygen, one of two things can happen: The site where the oxygen has reacted can cleave off a piece of the fatty acid. The piece that cleaves off will become a smaller acid or related molecule. These smaller acids have a strong and characteristic smell that can be detected in tiny concentrations. These same acids are made by bacteria during fermentation and culturing, and result in the characteristic odor of many cheeses, buttermilk, bread, etc. When these odors are associated with fats and oils that have reacted with oxygen we say the oil has become rancid.

After reacting with oxygen, in addition to breaking off a piece of the fatty acid molecule to make a smaller smelly acid, the triglyceride molecule can attach to another triglyceride molecule. The resulting molecule is twice as large, less volatile and more viscous. The driers added to linseed oil and varnish simply speed the reaction of the hydrogen-deficient carbon atoms with oxygen.

The various fats and oils differ from one another in how many of their carbon atoms are deficient in hydrogen and therefore are more or less prone to react with oxygen. If there are a lot of deficiencies, as in the case of linseed oil or walnut oil, there will be a greater probability of one triglyceride molecule adding itself to another. After exposure to oxygen for some time, lots of triglyceride molecules will have added to one another to make a giant molecule we call a polymer. Polymers are tough and rubbery and make a good coating. We refer to this chemistry of adding together triglyceride molecules to make a tough film as curing or drying the oil. Chemists call it polymerization and crosslinking. In addition to curing or drying, the oil will also be splitting off smaller volatile acids and related chemicals that give these films their characteristic odor, especially in a confined space.

Oils like olive oil and saffron oil have fewer carbon atoms deficient in hydrogen. They can't react enough to make a tough film. They don't even react enough to generate many smaller stinky acids. In between are the oils like soy and corn. They will react with oxygen to generate smaller acids and they will react with one another to make big molecules; but, they don't react (cure) enough, or in a short-enough time, to be as good as linseed oil or walnut oil for furniture finishing. Nevertheless, they cure enough to stick well to a cutting board.

The fats and oils that accumulate with use on a cutting board, as well as the accepted walnut oil -- or anything else with an organic oil in its name, e.g., linseed, tung, etc. -- experience identical reaction with oxygen to generate the same volatile products as adding some oil from the cooking oil bottle. So, for a cutting board that gets used, it will smell the same whether it gets freshened up with oil from the cooking-oil bottle or not.