“I wouldn’t do it,” warned Michael J. Tarkanian, senior lecturer at MIT’s Department of Materials Science and Engineering. His specialties include metallurgy and the fatigue and failure of materials. Kyle Cooper of Bernal Cutlery in San Francisco couldn’t agree more: “What I typically tell customers who ask about this is, ‘Don’t.’"
But why not, exactly? And does the material of the knife’s blade matter at all?
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What Happens to a Carbon-Steel Blade in the Dishwasher?
“The temperature and pressure of the water, the potential corrosivity of the detergent, and movement of the knife in the dishwasher (i.e. collisions with other objects) could all contribute to dulling of the edge, or a changing of the patina in the case of a carbon-steel knife,” Tarkanian said.
Carbon-steel blades are in serious danger, Cooper agreed: “The main problem that we see is the long-term or repeated exposure to moisture. For carbon-steel blades, ‘long-term’ can be as little as 10 minutes, so a full cycle in a dishwasher will do fairly significant damage in the form of corrosion. Most knives can be buffed back to life, but repeated instances of this will dramatically limit the usability of a carbon-steel blade.”
What Happens to a Stainless-Steel Blade in the Dishwasher?
Stainless-steel chef’s knives are not immune either, he added. “Their blades are stainless, not stain (or rust) proof.” While regular stainless-steel tableware can go in the dishwasher with no problems, it is made of softer steel that can resist corrosion.
But chef’s knives need to be able to hold a sharp edge, so they are made from a harder version of stainless steel that is less corrosion resistant, Cooper explained. These “stainless blades can survive many rounds in a dishwasher . . . (but) the rust will come eventually (and that) will cause it to become duller faster.”
What Happens to a Knife’s Handle in the Dishwasher?
Degraded handles are probably the “most noticeable effect of a knife in the dishwasher,” Cooper says. “Uni-bodied rubber and plastic handles are usually fine, but the Western-style riveted handles and wooden Japanese-style handles will eventually fall apart.”
The main issue is the “drastic temperature fluctuations,” your knife’s handle will be subjected to, Cooper adds. The handle will “expand and contract, allowing the moisture to soak into the seams . . . and probably never completely dry out.” Splitting and cracking is another common problem.
“I never thought I would be this passionate about anything related to a dishwasher,” Cooper added. “But here we are.”
Bottom line? “Hand washing and drying will be safer,” Tarkanian affirmed.
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So, How Should You Wash a Chef’s Knife?
Since even a stainless-steel knife isn’t corrosion-proof, try not to leave it wet and dirty for long stretches every time you cook.
Holding it by the handle, rinse with hot tap water, and run a soapy sponge over the blade, starting from the spine—the side away from the sharp edge. Don’t travel along the sharp edge—or you’ll cut up your sponge. (Trust me, I have the sliced sponges to prove this.)
Be sure to detail the top of the handle where it joins the blade, and don’t forget to (gently) wash the handle itself, particularly if you’ve been handling raw meat.
Rinse the whole knife, and pat dry immediately. Again, be sure to move the cloth across the blade starting from the spine—never travel along the sharp edge. Store the knife safely, hopefully on a magnetic knife strip, in a knife block or another storage device, so the sharp edge isn’t dangerously exposed, or able to bump into other objects and get chipped or dull.
Photo credit: Rick Neves via Getty Images