Wisdom Behind The Wood #7: Janka Hardness

Wisdom Behind The Wood #7: Janka Hardness

Welcome back to the seventh installment of Wisdom Behind The Wood! I've mentioned the Janka hardness scale for cutting boards in a number of my previous blog posts. In this installment, I'll explore the history and applications the Janka scale has for cutting boards.

Why does wood density or hardness matter in a cutting board?

In cutting boards, there’s a balance to strike between three different things. The first is the feedback (or the knife feel) that the cutting board gives as you use it. Imagine dropping a marble on a piece of concrete. Now imagine dropping that same marble on a piece of plush carpet. The effect would be VERY different. So, too, with cutting boards. In general, super dense materials (glass, some synthetic materials, stone, really dense hardwoods) will give very aggressive feedback, resulting in a knife bouncing uncomfortably on the cutting surface as you chop on it. Some plastic cutting boards, on the other hand, are extremely soft, resulting in a very muted, unsatisfying knife feel. There’s a critical middle ground to find, where the feedback you get from using the cutting board is ‘just right.’

A second consideration is a cutting board’s resistance to getting scarred up over time with knife marks. In general, an extremely dense material will resist scratching better than a less dense material. For example, I could chop carrots on a piece of granite all day long and it would leave nary a mark. But if I chopped all day on a piece of balsa wood, the cutting surface would look like it had been chewed by an angry beaver.

A final consideration on density is the cutting board’s impact on knife sharpness over time. In general, the softer the material, the gentler it will be on knife edges. Hinoki (in the softwood cypress family) will be much gentler on a knife edge than lignum vitae (ironwood).

Because knife edge retention benefits from a softer cutting board, and resistance to scarring benefits from a harder cutting board, we try to strike a balance between the two factors when we select the wood species we use. Fabricating our boards using end grain construction gives us an additional ‘cheat code,’ giving the same great knife feedback, while giving additional resistance to knife marks over time.

How is hardness measured?

The Janka hardness test was invented by Austrian researcher Gabriel Janka in 1906. The test measures the amount of force required to drive a 7/16" diameter steel ball halfway into a sample of wood. Testing is always carried out on heartwood, with wood at 12% moisture content, and the sample must be free of knots. Janka borrowed heavily from the Brinell hardness test (created in 1900) which similarly uses a carbide ball to create an indention into metal samples.

Practical Application

The Janka hardness scale for cutting boards can be a useful metric when considering which one to purchase. However, there are many other factors that need to be considered such as: silica content, porosity, stability, availability/cost, sustainability, aesthetics, etc.

Bamboo is a popular choice amongst Amazon and grocery store aisles. It is low cost and it has a Janka rating similar to hard maple (1380). However, bamboo is extremely high in silica and will dull knife edges aggressively. Cutting boards marketed as "Teak" (3,540) are another popular choice, but Teak is extremely hard and full of silica. Beech (1,300) is fine for a utility cutting board and is commonly sold in Europe for that purpose. It’s a little more prone to cracking and slightly less attractive looking than other wood cutting boards.

So why does the Boardsmith use the woods that we use?

After years of experimentation and study, the Boardsmith settled on three main wood species for our butcher block: Hard Maple (1450), Black Walnut (1010), and Black Cherry (950). For detailed write-ups on each species check out these previous blog posts: Hard Maple, Black Walnut, and Black Cherry. While there are subtle differences between the three, they all excel at durability, knife edge retention and knife feel. Sustainability is important to us and each wood species we utilize is a domestic hardwood grown and harvested in sustainable forests in the U.S.A. If there was a better wood species to make butcher block from, we would use it. No matter your aesthetic preference of wood species, a Boardsmith butcher block is the best butcher block.


About Nolan Russell

Nolan Russell is the Operations Manager at The Boardsmith. His blog segment dives deeper into the trees, lumber, and the science that make our butcher block the best in the world. Nolan is a Certified Arborist, former Tree Care Professional, and all-around tree nerd.

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