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How brittle is a Japanese knife – chipping & breaking

Japanese knife durability

First-time Japanese knife buyers are scared of breaking or chipping their new Japanese knife but are they that brittle, or are they more durable than we think?

Rockwell Hardness

A lot has changed with Japanese knives, and there are multiple options available. One of the metrics we can follow is the Rockwell Hardness. In general, you can say the higher the Rockwell, the longer the edge retention and the sharper it can get. However, the higher the Rockwell, the more brittle the knife. A low Rockwell has the opposite effect. You lose edge retention with a lower Rockwell but get more durability. 

Shibata Takayuki – Kotetsu Type III – Aogami Super

Japanese knives

While the Rockwell can say a lot, we have to dive deeper into the Japanese knives before understanding why the knives are more brittle and what we can do about them. With the many modifications to suit a specific audience, the differences between a Japanese knife and other knives are slimmed down. Therefore I will only cover the most common differences. 

Makoto Kurosaki – Shirogami White #2

Thinner knife

Most Japanese knives are thinner and harder than others. When a knife is thin and hard, there is a more significant chance of breaking. It is because a harder knife is less flexible and can break on hard impact. Therefore I don’t recommend crushing things with the sides of a hard Japanese knife. To reduce the fracture rate, they can do a few things. You can make the knife thicker, or you can sandwich them between 2 softer pieces of steel.  

Hardness & Cladding

To reduce the harder and thinner steel’s fracture rate, especially with Japanese knives with a high Rockwell of 61 and beyond, they needed to sandwich the harder steel with two softer steel because the softer steel is more bendable. The knife fracture rate is drastically reduced if you sandwich the hard steel with two outer softer steel.

Shibata Takayuki – Kotetsu Type III – Aogami Super
Cladding example
Cladding example
Cladding example: Al Dente
Cladding example: Al Dente

Brittleness

Most new Japanese knife owners are scared to use them because of the brittleness. Some have already chipped them or has multiple microchips along the cutting edge.

Kai Shun Santoku Classic
Kai Shun Santoku Classic

Cladding

While the cladding is excellent for the added durability and drastically reduces the fracture rate. The harder-core below the cladding line is still exposed and not protected. 

Sharpened angle

Most Japanese knife enthusiasts are obsessed with thin knives, especially behind the edge. That is why they love to look at the choil of a knife. We know that most Japanese knives have a lower sharpened angle, which makes the cutting edge extremely thin and extra fragile. The thinness gives you sharper performance, and the hardness of the steel is how you keep the sharper performance for a longer period.   

Choil of Yu Kurosaki and Shibata knives
Choil of Yu Kurosaki and Shibata knives

Durability

The knives can easily last you a decade or more without having to thin out the knife if you take proper care. With good care, you will see that the knife is a lot more durable than we think. Just like an egg, the shell is fragile on impact; however, it is incredibly durable and won’t crack in your hand no matter how much force you apply. In this example, your hand is acting as a cladding for the egg. But a simple tap on a flat surface will easily crack the egg. 

Choil of Yu Kurosaki and Shibata knives
Choil of Yu Kurosaki and Shibata knives

Wrong usage/what not to do

If you want the knife to last more than a decade, you should not do the following things. 

Excessive force, Frozen Food, Bones

Because of the thinner and harder knife, you should not use excessive force or force your way through some food. You can think about mincing onion, let the knife do the work for you, and don’t force your knife or dig your knife in the cutting board. The same applies to Frozen food or bones. Don’t try to force your way through anything but let the knife do the work for you.  

Global Santoku
Global Santoku

Scraping on the cutting board

What most people also like to do is scraping the food together with the cutting edge. While combining this motion with some force, you increase the chipping rate and one of the reasons you see microchips across the cutting edge on Japanese knives with a high Rockwell rating. 

Kai Shun Santoku Classic
Kai Shun Santoku Classic

Twisting the blade

The same applies to the twisting motion, and you should always cut completely through some food like root vegetables and do not twist the knife to break the food off. 

Kai Shun Santoku Classic
Kai Shun Santoku Classic

Don’t cut cheese

I don’t recommend a thin and high Rockwell knife on cheese. As you know, by simply twisting and scraping, you can damage the cutting core. The cheese will cling to your knife, or if it is a hard cheese, it may even chip the knife when you accidentally twist the knife mid-way. 

Only suggestions

Of course, what I explained is only a suggestion, but I hope you understand why we don’t do certain things based on what we know about Japanese knives with a high Rockwell hardness and a thin cutting edge. 

Maintenance & care

Once you understand what you can and can do, the knife will easily last you a decade or even a lifetime with proper care and maintenance. And it would be best if you always hand-washed your knives. 

Kai Shun Santoku Classic

Single Bevel

While I did not talk about single bevel knives, the knife’s cutting edge is even thinner and more fragile than the double-beveled Japanese knives. 

Questions

If you have any questions or doubt about what you can or can not do, leave them in the comment section below. 

Knives used in this video:
Makoto Kurosaki – Shirogami White #2
Shibata Takayuki – Kotetsu Type III – Aogami Super
Yu Kurosaki Shizuku Gyuto – SG2/R2

🛒S H O P:

Kai Shun Santoku Classic:
NA: Kai Shun Santoku Classic
EU: Kai Shun Santoku Classic

Kai Shun Official Amazon Store:
NA: Kai Shun Official Amazon Store
EU: Kai Shun Official Amazon Store

Global Official Amazon Store:
NA: Global Official Amazon Store
EU: Global Official Amazon Store

Wusthof Ikon Classic:
NA: Wusthof Ikon Classic
EU: Wusthof Ikon Classic

Zwilling Pro:
NA: Zwilling Pro
EU: Zwilling Pro

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Hi, I'm ChefPanko, I have worked for multiple restaurants and have decided to share my experience with you guys. I will share recipes and techniques that I have learned, taken, and improved from the French, Japanese restaurants that I have worked for. I will also explore other cuisines with you guys.

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One Comment

  1. Extra information on why I don’t recommend cutting through cheese, hard bread, etc:
    While we eat a lot of cheese in the West, the Japanese people with the old tradition don’t consume cheese or dairy. With the fusion and modernization of countries, you slowly see more and more diary in Japan (Pizza, Pasta, etc.).

    You now see that Japanese knives are adapting to the western cuisines; (western handle design thicker knife, cladding compared to the traditional Japanese knives and single bevels)
    This knife, particularly (60 HRC), should be able to go through hard cheese.

    The problem is that high Rockwell knives around 61+ have longer edge retention but sacrifice durability.

    So an accidental twist combined with a thin edge and high Rockwell (even 60HRC) will result in an increased rate of chipping due to improper use.
    Soft cheese causes a problem too since the softer cheese clings onto the knife, and the thin cutting edge cant handle the drag and will get multiple stress fractures.
    Hard cheese, if accidentally twisting the knife while the knife was still in the cheese block, can cause chipping.

    To avoid multiple stress fractures around the blade, they have added softer cladding to protect the core.
    But this also means that you should not use the knife to crush the garlic, especially if done in high volume or tenderize meat with those kinds of knives.
    The multiple stress fracture will build up over time, and especially knives without cladding can suddenly break.

    Meanwhile, softer knives like the german chef’s knives are softer, around 58 Rockwell or lower, which can handle any abuse.
    The edge will roll rather than chip or break, but it sacrifices edge retention/sharpness for the increased durability since it is softer.

    To reduce drag on soft cheese, you have cheese knives with holes so that the cheese won’t cling to the blade.

    For this reason alone, I always have a beater knife (a cheap knife with soft steel). When I’m at home, I don’t always cook occasionally, I have a frozen pizza, and I don’t have a pizza cutter, so I use my softer cheap knife to cut through it. I basically use it on things that I will never slice or cut with a high carbon thin Japanese-styled knife.

    Hope that this explains why I advise against going through the cheese and other hard food.

    As with bread, the hard crust is unpredictable and sometimes can be very hard, therefore they have a serrated bread knife with an asymmetrical grind. The teeth bite in the crust and the asymmetrical design adds durability and will saw through the softer layer.

    Extra information about breaking rate/stress fracture:

    Using high HRC blades to crush garlic, nuts, etc. The stress can be distributed by using the side of the blade near the spine/handle.

    Blade construction has a major effect on strength/durability.

    Western knives are most commonly mono-steel (one layer) so they are often limited to hardness below 60. Even premium steels are risky above 60 in a mono construction.
    -True Damascus. Multi-layer construction with no discrete core material. This is generally not as strong as other constructions since there are multiple stress risers on the cutting edge. There is a legend that some of these old Damascus blades were “nearly unbreakable” but I doubt that they would compare to modern steels.
    There is an interesting modern take on this construction using 2 different stainless materials.

    San Mai (3-layer) with a hard core and softer (and usually more stain-resistant outer core). These blades can have a practical hardness limit above 60.
    A subset of San Mai is modern Damascus. These are really a 3 layer construction with a hard core and multi-steel outer layers
    Honyaki (differential heat treated mono-steel). These can be hardened above 60 but generally are not as desirable as San Mai for ultimate hardness/strength.

    Most tough blades are layered construction such as San Mai. I’m a fan of San Mai construction as it can reduce the stress on the hard core. Exceeding stress limit is what leads to failure. In bending or torsion; stress is proportional to strain and strain is proportional to thickness. The thinner the hard steel is the more it can be bent before the stress limit is exceeded. This is why you can make a flexible glass cable. Each fiber is so thin that the strain is reduced and the stress limit isn’t exceeded. If the same diameter cable was made from solid glass it would have almost zero strain limit. It would be very stiff and require a high force to bend. But if bent even the slightest bend will likely cause a fracture.

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