Why Using a Dishwasher to Clean Japanese Knives is a Bad Idea

Like most people, you probably believed you'd never have to wash dishes by hand again after you got a dishwasher. Hold on a second. Your knife, which you probably use several times daily, is one of the few kitchen implements that should not be cleaned in the dishwasher. It's rare and pricey, and the dishwasher is killing it slowly.

The Truth About Your Knife and the Dishwasher

To begin with, there is the oppressive heat and muggy air. You probably despise being sweaty and drenched, and neither does your knife. Steel and handles are especially vulnerable to a dishwasher's intense heat and moisture. In particular, if your knife is made of carbon steel (which rusts easily) and has a wooden handle, you should take this precaution. Then, the turbulent air arrives.

Japanese Knife

A knife's edge is especially vulnerable to the water jets in a dishwasher, which can also cause the knife to bang around and potentially damage other dishes.

Furthermore, ceramic knives are especially vulnerable due to their fragility. The blade can be chipped or broken in half in a single cycle. Additionally, detergents can be as dangerous as the machinery itself, as they can dull or discolour knives.

Last but not least, there's the issue of everything else—including your fingers when you unload the dishwasher—that you put there. Glasses, plates, and the machine are fair game for your knives. Injuries are possible if you point them up, while utensil baskets are damaged if you point them down.

Why You Should Not Use Dishwasher to clean Japanese knives? — Frequently Asked Questions

How fast will a single dishwasher cycle damage my Japanese knife?

Faster than you'd expect. One cycle: noticeable edge dulling from the alkaline detergent and the high-temperature wash. Two to three cycles: visible spotting or rust on a carbon-steel blade. Five to ten cycles over a few months: the wooden handle (especially wa handles) starts loosening as the wood expands and contracts. After a year of regular dishwashing, even a $300 knife is meaningfully damaged in ways that are hard to reverse. The 30 seconds it takes to hand-wash genuinely save the knife.

I rinsed my knife and accidentally put it in the dishwasher anyway — what should I do now?

Pull it out as soon as you remember, hand-wash, dry completely, and inspect the edge with a tomato test. If the knife still bites a tomato on its own weight, you got lucky — wipe a thin film of food-safe oil if it's carbon steel and continue. If the edge has dulled noticeably, plan a sharpening session within the next week. If you see new rust spots, polish them off with a wine cork dipped in baking soda paste before they spread. Don't panic — one accidental cycle is recoverable; it's the repeated cycles that ruin the blade. Read our rust prevention guide.

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Are there any "dishwasher safe" Japanese knives?

Some lower-end Japanese stainless knives are marketed as dishwasher safe, but the marketing is more about avoiding warranty claims than about the dishwasher being good for the knife. Even on a "safe" stainless blade, repeated dishwasher cycles dull the edge faster than hand-washing, and the knife clanging against other items in the rack can chip the edge. The label means "won't structurally fail," not "performs well." Hand-wash anyway — it takes 30 seconds and adds years of cutting performance.

Why does the dishwasher specifically damage the handle?

Heat and humidity cycling. Wood expands when it absorbs moisture and contracts when it dries — a dishwasher cycle does both within an hour, repeatedly. Over many cycles, the wood swells and shrinks until the fit between handle and tang loosens, the rivets work loose on Western handles, and cracks develop along the grain. Wa-handle knives (Japanese style with hidden tang) are slightly more vulnerable because the friction-fit relies on the wood's tight grip; once the wood shrinks slightly, the blade can wobble. Hand-wash and the handle lasts decades.

Is hand-washing actually less hygienic than the dishwasher?

No — hand-washing with hot soapy water removes bacteria as effectively as a dishwasher cycle, and you don't leave the knife sitting in a damp environment for hours afterward. The dishwasher's "sanitize" cycle uses higher temperatures than hand-washing, but for a kitchen knife rinsed with hot water and dried immediately, that level of sanitization is overkill — there's no food residue left to harbor bacteria. The hygiene argument for dishwashing kitchen knives is mostly a misconception.

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About the author

Kei Nishida

Author, CEO Dream of Japan

info@dreamofJapan.com

Certification: PMP, BS in Computer Science

Education: Western Washington University

Kei Nishida is a passionate advocate of Japanese craftsmanship, a writer, and the founder and CEO of Japanese Knife Co., Japanese Green Tea Co., and Japanese Coffee Co., all part of Dream of Japan.

His journey began with a mission to introduce the world to the exquisite flavors of Japanese green tea. Through Japanese Green Tea Co., he pioneered the import of premium tea grown in nutrient-rich sugarcane soil, earning multiple Global Tea Champion awards. He then expanded into the world of coffee, launching Japanese Coffee Co., the first company to bring Sumiyaki charcoal-roasted coffee to a global audience.

With a deep appreciation for Japanese artistry and tradition, Kei turned his attention to one of Japan’s most revered crafts: bladesmithing. Through Japanese Knife Co., he made handcrafted katana-style knives, created by a renowned katana maker, available outside Japan for the first time. These exceptional knives embody centuries of samurai sword-making expertise, blending tradition with modern functionality for chefs and collectors alike.

Kei’s journey continues as he uncovers and shares Japan’s hidden treasures—one sip, one blade, and one legacy at a time.