Purpose of mineral oil in cutting boards

[Matt Campbell]

Besides enhancing appearance, what would you say is the purpose of mineral oil in end-grain cutting boards? Initially, I thought it was to keep liquids from soaking down into the wood, but that will happen no matter what. Plus you actually want liquids from the food (especially meats) to soak into the wood. Reason being, bacteria needs moisture to live. If you take away the moisture, then you take away the bacteria. So if you finish end-grain cutting boards with mineral oil, aren't you giving bacteria what it needs to live?

[Brian Kent]

I don't know a technical, official answer, but…

Like you said, it looks good.

The oil swells the cells and makes the grain drain.

Oil and water don't mix. Having the grain filled with oil keeps the meat juices from finding a deep-down home.

Like you said, it looks good.


Brian

[Brian Effinger]

Hey Matt,
Check out the wood whisperer's site. He's got some good advice on cutting board finishes (http://thewoodwhisperer.com/cutting-board-finish/). He also did a podcast, which is linked in the article.

Brian

[Matt Campbell]

Even after reading that article and several comments, I'm still not sure. Unless the people who use them re-oil them all the time, water will never really be completely repelled.

[Brian Kent]

Yes, we re-oil them as often as needed.

[Frank Drew]

Mineral oil is food safe, safe for human consumption; I think that's the main reason it's traditionally used with butcher blocks and cutting boards.

[Jeff Bratt]

You actually don't want meat juices soaking into the board. However, on an end-grain wood cutting board, water will never be completely repelled. What you are looking for is water resistance, to make cleaning easier and to avoid stains. The structure of the wood gives it natural anti-bacteria (http://faculty.vetmed.ucdavis.edu/faculty/docliver/Research/cuttingboard.htm) properties. Mineral oil, with or without beeswax is the traditional treatment. Mark likes salad bowl finish. I like walnut oil. In any case, flood the surface several times - the end-grain soaks up lots of whatever finish you use. And the surface treatment will need to be renewed - how often depends on how much the board is used. In commercial service, this could be every day. On mine, it's every 3-6 months.

[Rob Young]

Plus you actually want liquids from the food (especially meats) to soak into the wood. Reason being, bacteria needs moisture to live. If you take away the moisture, then you take away the bacteria. So if you finish end-grain cutting boards with mineral oil, aren't you giving bacteria what it needs to live?

Nope. The opposite, you are denying the moisture a place in the board.

[Matt Campbell]

Unless the board is completely saturated, I don't think that would happen. And on a practical level, most or all people who use these won't continually soak the board in oil. That's just too much work.

The reason I'm giving so much thought to this is that I have a few local stores wanting to sell these. So of course I'd like to make these as safe as they can be.

[Dan Forman]

My understanding of the argument is that it's not really that you want the board to absorb juices, but that in theory, unfinished boards are antiseptic because the wood absorbs moisture from any bacteria which might be left on the surface of the board, dehydrating them. A finished board theoretically won't do that, so, like a plastic cutting board, will harbor live bacteria in the knife cuts that accumulate over time. There seems to be little consensus however, or at least that's what I found when I was looking into this a year or so ago.

The other side of the coin, is that a finished board is less likely to crack due to fluctuation of moisture in the wood, and may stand up to knife damage better than an unfinished board.

Dan

[Anthony Whitesell]

Any idea what Salad Bowl Finish actually is? Is it possible to mix your own homemade salad bowl finish?

[Joe Chritz]

Salad bowl finish is a thinned varnish. You could approximate is somewhat with thinning any varnish substantially with mineral spirits.

If you form a film it is put on to heavy. For that reason mineral oil and/or mineral oil/wax is the only finish I ever use on cutting boards.

Even the scientists and experts can't agree on wood vs plastic or finished/unfinished. Thousands of boards are made and sold that give instructions to use mineral oil for many many years.

I am a subscriber to the "if it isn't broke don't break it" philosophy.

Joe

[Bill White]

To keep ya lubed up while you're eating all those wood splinters. UHMW cutting boards for my kitchen. They go in the dishwasher, and I sand 'em about once a year.:p

[Anthony Whitesell]

I changed from the UHMW cutting boards to the acrylic. The acrylic boards don't get the knife marks in them like the UHMW ones do.

P.S. I also don't have a dishwasher.

[Brad Wood]

Ever seen a butcher block top in a kitchen that has not been oiled regulary over years? They tend to dry up and split/crack.

Years ago (like 20) I was in a multi million dollar house outside the L.A. area, it was an advocado ranch and a huge house, so probably tens of millions... anyway, beautiful house and kitchen, total gourmet setup in the kitchen. They had a huge butcher block for the island and it was never taken care of... looked awful, cracked, ugly. We were able to get a whole bottle of mineral oil to soak into that thing over a couple days, and it looked a lot better by the time we left (we were there filming a video on wine tasting and the counter was in the shot, so we needed to do something to get it to look better.. so, this was way before I got into woodworking). So... while there may be merit to preventing water to soak in, or bacteria, etc, etc, I think the number one reason in my head is to keep the wood healthy looking. Secondary is they just look better.

[Jose Kilpatrick]

The old timers that used wood cutting boards for cutting meat, covered the entire area with a thin layer of salt after use and let it set that way for a spell. The salt supposedly prevents bacteria from getting a strong hold and is supposedly how you tackle the whole sanitary aspect of using a wood cutting board. There's some debate on wood vs. plastic cutting boards based on the fact that wood is an organic substance that certain bactera, fungus and molds can eat where plastic is not. But, the debate seems to stem from the fact that an scarred up plastic cutting board can harbor bacteria in tiny cracks that are not cleaned well.

The purpose of using oil on a cutting board is to prevent liquids from seeping into the grain. Primarily for sanitary reasons and also to prevent it from staining. There are also claims that a wooden cutting board is better at preventing a bacteria bloom because of the natural chemicals in the wood that are there to protect it from microscopic invaders as a living organism. This goes against the whole wood being an organic material that can feed bacteria. But more evidence shows that wood cutting boards to more sanitary to use than plastic.

If you choose an oil, stay away from vegetable based oils as they turn rancid over time.

[David Keller NC]

From the standpoint of marketing cutting boards, you're best off with a wax-based (preferably beeswax) coating or mineral oil. Pure (and genuine) tung oil, modern linseed oil, shellac and modern alkyd varnish are all completely non-toxic when cured, but your average joe doesn't know this, and there's a raft of people without the scientific expertise to offer a worthwhile opinion telling the general public that finish manufacturers are trying to poison them with "chemicals".

So in that sense, you may have an easier time finishing the boards with something that is identified as a food-grade material that is FDA listed for inclusion in food stuffs. Shellac, beeswax and to a certain extent, mineral oil meet these criteria (mineral oil content is regulated to a certain percentage because of its tendency to cause diarrahea in large amounts).

From the standpoint of bacterial growth, all surfaces in the average home will be coated with bacteria - no matter how much the homeowner cleans such surfaces. The exception are dishes (and cutting boards) that have just come out of the hot cycle in a dishwasher, or hand-washed with liquid soap (soap is an incredibly effective bacteriocide). Once those dishes or cutting boards are exposed to room air for more than a few minutes, bacteria can be recovered from them with microbiological laboratory techniques.

But from the standpoint of safety, it's a question of amount and type. Most humans, unless severely immune compromised, can tolerate several hundred to several thousand salmonella organisms without becoming ill, depending on the strain. Most humans will get violently ill with ingestion of several dozen Listeria organisms. Moreover, most disease-causing bacteria that are associated with food spoilage will not survive in an aerobic (oxygen-containing) atmosphere, nor in an oxygen-deficient atmosphere that is appreciably acidic. The problem is with anaerobic (oxygen-deficient) conditions that are neutral to slightly basic. This is why one can get botulism poisoning from canned meat products (like stews), but not from canned pickles or tomatos.

With respect to wooden end-grain cutting boards vs. plastic - it's correct that both can harbor bacteria, and the amount sensitively depends on the roughness of the surface. This is why a rough plastic cutting board can be a problem unless it's sterilized in a dishwasher. Wooden cutting boards have, in one sense, an advantage. Most woods will produce a slightly acidic environment on their surface, which kills harmful bacteria. Woods that have active anti-bacterial properties (a notable example being black walnut) will kill bacteria very swiftly.

[Matt Campbell]

Wow, David. What an informative post. Thanks so much. Can you tell me more about the anti-bacterial properties of walnut? What other woods have anti-bacterial properties? Maybe it'd be easier to point me to a source to read about this.

[hank dekeyser]

I've been using everyday common veg oil on my boards for years with zero problems. The only time I have trouble is if I get lazy and don't oil it. Personally I would have a small "sample" board on display (oiled, waxed, whatever) and a simple set of instructions included explaining the proper care of a wooden cutting board. (that's what I do when giving a board as a gift, etc) That way your butt is covered and there's no liabilty issues (hey ya never know what some people might claim to be allergic to, and take you for eveything you own) I've heard time and again the oiling schedule is -every day for the first week, every week for the first month, every month thereafter. Me - I just oil it when it gets a little dull looking.

[David Keller NC]

"Wow, David. What an informative post. Thanks so much. Can you tell me more about the anti-bacterial properties of walnut? What other woods have anti-bacterial properties? Maybe it'd be easier to point me to a source to read about this."

Matt - I'll have to do some searching to come up with some sources. I know I've read an actual study on this before, where bacteria were coated onto various wooden and plastic surfaces, and sampled through time. The walnut I remember to be almost sterile after about 30 minutes under wet conditions.

If you think about it, this makes sense. While black walnut heartwood will eventually be consumed when laying on a forest floor in direct contact with the dirt, it will last, in some cases, decades. The other forest species like red oak and especially maple will be gone after just a couple to three years. Walnut's also highly resistant to insect attack as well.

There are a lot of antecdotes about the anti-bacterial and anti-fungal properties of the heartwood of most tropical rainforest species. Even mahogany is quite resistant. However, if I was making cutting boards, I would be cautious about including tropical species. Mahogany's fine, but some of these woods can provoke severe allergic reactions - Goncalo Alves is a good example.

[Dave Lehnert]

Any idea what Salad Bowl Finish actually is? Is it possible to mix your own homemade salad bowl finish?

We have a woodworking store here in town that is owned by one of the best in finishing I have run into. They were showing me that salad bowl finish was nothing more than there regular varnish (poly) but sold for twice the price.
It was nothing more than playing on peoples fears of a safe finish.

[David Keller NC]

Matt - This link is not a primary source (in other words, the original article), but might be helpful:

http://www.naturalhandyman.com/iip/infxtra/infcuttingboard.html

This is a pertinent excerpt from the article:

"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. Scanning electron micrographs revealed highly significant damage to plastic surfaces from knife cuts."

I know that the University of Wisconsin did a similar study a while back - still looking for the original. There is a list of primary sources at the bottom of the webpage, but unfortunately I don't have access to PubMed, so I can't get the entire text of the journal articles.

This particular study found no difference between wood species, though I have read studies that drew different conclusions in comparisons between several domestic species including black walnut, cherry, maple, pine, etc...

[Rob Diz]

thanks all - this is very timely for me. I'm building a kitchen island with a 1 3/4 slab walnut top. I'm in discussions with my wife if it will have a film finish or a mineral oil finish and be used for cutting. My sense is that it will be the latter.

One local finish guru suggested that for the first application, heat up minearl oil 6 parts to 1 part parrafin wax in a double boiler. Apply that mix to both sides of the board and let it sit overnight, then scrape off the extra wax, and apply minearl oil to both sides. Then re-apply the minearl oil avery few weeks/month - let it sit overnight, and wipe it off in the a.m.

As it happens, right now I have a "wealth" of wide thick walnut slabs, so I think I will try the mineral oil top first, simply becuase it is so easy to repair and allows the use of knives on the top. I touch with the ROS, and all can look like new again . . .if ever desired. If it looks like crap after a few months, I'll just make another top, and cut up that top for use in another project with thinner pieces.

[David Keller NC]

"One local finish guru suggested that for the first application, heat up minearl oil 6 parts to 1 part parrafin wax in a double boiler. Apply that mix to both sides of the board and let it sit overnight, then scrape off the extra wax, and apply minearl oil to both sides. Then re-apply the minearl oil avery few weeks/month - let it sit overnight, and wipe it off in the a.m."

While interesting from a nerdy chemical engineering perspective (guilty as charged, I am), this is not necessary, and sounds really messy. If you wish to do something a little less like alchemy, you can simply apply mineral oil until you get the look you like, apply a paste-wax finish over top of it, allow the mineral spirits carrier in the paste wax to flash off, and buff it. The mineral oil will never "set" the way that linseed or tung oil will, so it will be eventually washed away by the repeated wipings with a damp cloth, in which case you simply re-apply it until it looks good.

It's debateable whether the mineral oil really has any protective qualities; the wax will simply give you a very short-term (like 5 minutes) opportunity to wipe the spill up - it will make most liquids that do not have surfactants (like dishwashing soap) in them bead on the surface.