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My wooden cutting board is turning black!

I tried reposition the cutting board and even tried hanging them but regardless of the different configuration, water still accumulate at a certain region during the drying process and blacken them. After the cutting board is dried, the black remains and is not fading away.

How to avoid it and how can I get rid of the black-ness?

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2 Answers 2

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The black spots can be one of several things, but are likely a variety of mold. Black stains can also be caused by a reaction to the iron in your knives (particularly if you use carbon steel blades instead of stainless steel). If it is mold, it is growing because even though the surface of your cutting board is dry, moisture has soaked in, probably because it needs to be oiled or waxed.

To recondition a butcher block or cutting board that is stained or gouged, you can sand the surface down, and reoil.

  1. Use a sanding block to keep the surface from getting wavy as you sand.
  2. Start sanding with 120 grit (80 if you are removing big gouges), and sand evenly, moving with the grain, until the stains are gone, or almost gone (if a few very deep ones survive, don't worry about it).
  3. Repeat the sanding with 240, then 400 grit until the roughness from the previous sanding is gone.
  4. Reoil with any Butcher Block Conditioner. There are many out there, and they are either food-safe mineral oil, or that oil with a few other waxes mixed in. Many are good, but my favorite is Howard's Butcher Block Conditioner. Follow the instructions, but it will amount to making a liberal application, allowing it to sit for a while, then wiping off the excess.
  5. Maintain the new surface by drying the cutting board well before storing (as you are already doing), and wiping lightly with mineral oil briefly every few times you use it, much like maintaining a cast iron pan.
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I would add bleaching the black spots (using a 1% bleach solution) before starting sanding to the steps above. –  FuzzyChef Feb 28 '12 at 4:43

After normal use, wash the board with a stiff brush and running water. Then wipe dry and leave the wooden board to fully dry by a window so UV light can get to it

Once every few months (depending how often you use it) weight the board down with something heavy (glass container etc.) into a strong brine solution for an overnight soak. Remember to dry and re-oil with your favourite wood oil (cooking oil may promote black mould growth) after this treatment. There are many opinions on what a good wood oil is. See separate discussions

Once you have the black mould stains, they are hard to remove without physical damage to the board. The simplest treatment is to send the board off to a wood worker to run through a "thicknesser" machine (high speed wood plane), and a manual plane on the edges

Do not sand wood that is not going to be painted. Sanding opens up all the ends of the wood fibres, and makes then soft, and absorbent, which will result in you board wearing out fast, and it absorbing more contaminants

If using mineral oil make sure it is food grade

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What kind wood oil to re-oil it? When and under what condition should I re-oil it? Can you edited with some references / links? thanks –  KMC Feb 27 '12 at 1:27
    
A thicknesser would be a great way to do it, but carefully done, sanding closed-pore woods like maple or cherry won't make the surface soft and absorbent. That would be a more likely problem with open-pore woods like oak. –  Sam Ley Feb 27 '12 at 2:19
    
@Sam Ley cutting boards should be softwoods, not hardwood - pine, bamboo, Kauri etc –  TFD Feb 27 '12 at 4:16
    
That would be a matter of debate (softwood/hardwood/edge grain/end grain), but you are right that if your cutting board IS a softwood, then an edge tool will make a better final surface than sandpaper. If you don't have a thicknessing planer, then I'm a big fan of a well burnished "cabinet scraper" for putting a final surface on a softwood. The micro-edge slices the wood fibers very cleanly, which is what you are getting at, plus the tool is just a few bucks. –  Sam Ley Feb 27 '12 at 4:25
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After grinding the edge flat, you use a carbide burnisher to put a micro-cutting edge on it. A good burnished edge will cut quite quickly - I've finish scraped entire chairs and maple coffee tables this way. Not as fast as a thicknesser, but not so slow as to be impractical. But we've probably gone way beyond the scope of the Cooking SE here. ;) –  Sam Ley Feb 27 '12 at 22:13

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