Oak chopping boards

What is oak, exactly?

Oak is Quercus, a genus of about five hundred trees and shrubs across the northern hemisphere, from the cork oaks of Portugal to the live oaks of Louisiana. For timber, the ones that matter divide into two camps. The white oaks, which include the two British natives, the English oak Quercus robur and the sessile oak Quercus petraea, and the American white oak Quercus alba, are the barrel and boat woods. The red oaks, led by the American red oak Quercus rubra, are cheaper, pinker and more open.

The difference between the camps is the thing this whole page turns on. Both are ring-porous, and both start each year’s growth with a band of enormous vessels. But white oak plugs its old vessels with tyloses, balloon-like growths that seal the plumbing, and red oak does not. That is why a white oak barrel holds whisky and a red oak one leaks, and why a straight-grained stick of red oak can be used as a drinking straw. It is not a figure of speech.

Pores: the whole problem in one picture

Hardwoods carry water up the trunk in vessels, which appear on the end grain as pores. In maple and walnut the vessels are small and scattered, and the end grain is close to solid. Oak is different. Each spring the tree throws up a band of vessels so large you can see them with the naked eye, two to four rows deep, followed by summer wood of small pores and dense fibre. That is what makes the growth rings in oak so bold, and it is what makes oak a poor end-grain board. Every one of those spring vessels is an open tube, and on a butcher’s block they all point straight up at your food.

Water goes in and stays. So does meat juice, and so do the bacteria in it. Where a maple block dries out in an hour, an oak block stays damp inside its pores, and a damp, dark, nutrient-rich tube is exactly what bacteria want. White oak’s tyloses close some of the tubes; red oak’s stay open. Neither is good enough.

Tannin: why oak turns black

Oak is one of the most tannin-rich timbers in the world. Tannin is the astringent chemical that makes strong tea furry on the tongue and lets an oak barrel flavour a whisky, and oak bark was the raw material of the leather-tanning trade for two thousand years. In a chopping board it does two unwelcome things. It reacts with iron to form iron tannate, the blue-black pigment that ink was made from until the twentieth century. A wet carbon-steel knife laid on an oak board for an hour leaves a grey shadow; a cast-iron pan leaves a ring; the traces of iron in hard tap water leave a general greying that owners of oak worktops know well. And it reacts with acidic food, so lemon, tomato and vinegar leave their own pale or dark ghosts.

None of this is dangerous. Iron tannate is what medieval scribes wrote with, and the tannin in the board is the tannin in your Bordeaux. It is simply unsightly, and it does not wash out.

How hard is oak? The Janka test

Hardness is measured by pressing a steel ball 11.28 mm across into a block of dry wood until it has sunk to half its diameter, and recording the force in pounds-force (lbf). White oak needs 1,350 lbf on the side grain, English oak 1,120 and red oak 1,220. All of that is comfortably inside the range where a board is firm without being cruel to a knife. On the end grain the USDA measured white oak at 1,524 lbf. If hardness were the only test, oak would pass with room to spare. It is not the only test.

Is oak poisonous?

No. Nothing in oak timber is toxic, which is just as well, since a great deal of what we drink has spent years inside it. Acorns are bitter with tannin and can upset livestock that gorge on them, but the wood is inert. The caveat is for the trade: fine oak dust is a recognised cause of nasal cancer in people who breathed it for decades in furniture factories, which is why modern workshops extract it at source. It has no bearing on a finished board.

Silica, resin and knives

Oak has neither silica nor resin, so it will not blunt a knife the way bamboo or teak does, and its hardness is in the right range. If you cut on a flat oak board, your knife will be perfectly happy. The trouble is not the edge; it is what is happening in the pores beneath it.

Movement and stability

Wood shrinks as it dries and swells as it gets wet, more around the growth rings than across them. White oak’s ratio of 1.9 is moderate, but its total shrinkage is high, over 16 per cent by volume from green to dry, and flat-sawn oak has a reputation for cupping that every furniture maker learns early. Quartersawn oak, cut so the rings run at right angles to the face, is much better behaved, and shows the silver fleck of the big rays into the bargain. It is also considerably more expensive.

Where oak does belong

Everywhere else in the kitchen. Oak is a superb worktop wood, a fine wood for a serving board that will only ever meet bread and cheese, and the only wood for a barrel. Its open pores are exactly what a cooper wants, because the whisky can breathe through them a molecule at a time while the tyloses keep it from leaking out. Its tannin is the flavour of every red wine you have enjoyed. None of that makes it a butcher’s block. We say this as people who like oak very much.

Is oak sustainable?

Yes. American white oak and European oak are both listed as species of least concern, both are grown in managed forests across their ranges, and both are among the easiest hardwoods to buy with FSC or PEFC certification. Britain’s oak woods are a fraction of what they were before the shipwrights got to them, but the tree itself is in no danger. It is slow: a sawlog oak is eighty to a hundred and fifty years old, and an oak planted today is a gift to somebody’s great-grandchildren.

Five things you did not know about oak

1. A ship took a forest. HMS Victory used the timber of around six thousand oaks, which is roughly a hundred acres of woodland. Britain’s wars with France were, among other things, a contest over who had more oak.
2. Ink was made from it. Iron gall ink, the standard writing ink of Europe from the Middle Ages to the typewriter, was made by mixing oak galls, the swellings a wasp raises on oak twigs, with iron salts. The same reaction stains an oak board.
3. Whisky is mostly oak. Distillers reckon that sixty to eighty per cent of a whisky’s flavour comes from the cask. Bourbon must by law be aged in new charred white oak, and Scotland buys the barrels second-hand.
4. The pores explain the leak. Red oak was tried for barrels and abandoned; without tyloses it weeps. Coopers can tell red from white oak in the dark by blowing through a stave.
5. It hosts more life than any other British tree. An English oak supports well over two thousand species of insects, fungi, birds, lichens and mammals, more than any other native tree.

Our verdict

Buy oak for a worktop, a bread board or a cheese board, quartersawn if you can afford it, and never leave a wet knife on it. Do not buy an end-grain oak block. The open pores will hold what you would rather they did not, and the tannin will show you where every pan has been. For a block that stays clean and flat for decades, we build in maple and walnut, and we would say the same to a friend.

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