I was mistaken, they tested 5,000 cuts and checked after every 200. No real difference in knife sharpness after 5,000 cuts.
They did find the softer wood causes more dulling possibly due to the damaged wood making a rougher surface.
A good wood or bamboo cutting board can serve you well for years to come. Which model is best?
www.cooksillustrated.com
Grain Style Can Affect Durability
The way a board is constructed, or its grain style, can also play a role in determining how well it resists damage over time. In particular, end-grain boards, which are made from blocks of wood with their grain exposed on the cutting surface—are potentially more vulnerable to cracking and splitting. When using an edge-grain board, your knife slices against the grain. When using an end-grain board, your knife slices with the blocks' exposed grain. (Some folks think this makes end-grain boards gentler on the knife, but in our robot testing, there was no clear difference in sharpness between knives used on end-grain boards and knives used on edge-grain boards.)
Ordinarily, you're cutting with such low force when performing ordinary kitchen cutting tasks that no real damage is done to the board. But if you make a forceful cut on an end-grain board—as you would when using a cleaver—you are at a greater risk of splitting down the grain line than you would be if you were using an edge-grain board. Senalik compares the process to chopping firewood; The easiest way to split a log is by chopping it on its end, with the grain, not on its side, against the grain. Indeed, when we hacked up chicken parts with a cleaver on each of the boards, the only board that cracked was an end-grain model. Cracks are worrisome not only because they forecast a shorter lifespan for the board but also because they can harbor bacteria.
End-grain boards also absorb more moisture than edge-grain boards, increasing their susceptibility to damage. Matt Huffman, furniture maker and member of Fort Point Cabinetmakers, explained: As each block or plank absorbs moisture (for example, while the board is being washed), it swells, pushing against the surrounding blocks or planks. And as it dries out, it shrinks, pulling away. This process of expansion and contraction changes the precise dimensions of the wood and stresses the glue joints that connect them, making it more likely that the pieces of wood, both block and plank, will separate. The more water the wood absorbs, the greater the expansion and contraction. This was the case with the end-grain board that cracked; it drank up water so quickly that we could barely blot it dry, and it ended up separating along many of its glue lines.
Huffman also explained that end-grain boards have one more issue: They consist of many different blocks of wood, and each block of wood expands and contracts in different directions. Good woodworkers can account for the movement of each block and compensate accordingly, but this doesn't always happen with mass-produced boards. As a result, edge-grain boards are often more durable than end-grain boards simply because they have fewer moving parts—literally—and fewer glue joints that can fail over time.