Everybody keeps telling me don't put knives in dishwashers. And if I ask them why, nobody seems to have an answer or an argument to support his/her advice. So I thought I'll shoot the question to stackexchange:
Do knives get dull in dishwashers?
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1People only told me not to put bone-handled knives in dishwashers: and that for the sake of the handles.– ChrisWJun 25, 2011 at 17:53
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9Most dishwasher detergents are pretty reactive with many metals. You shouldn't be using harsh dishwasher detergent with real silver-ware for instance, or gold rimmed glasses. Dishwasher detergent has to be aggressive to work with so little mechanical scrubbing, whereas hand washing soap is much gentler, less reactive, since it is expected one will be using brushes or sponges to mechanically remove dirt. Stainless steel doesn't often react with dishwasher detergent. Aluminum develops an oxide layer that protects it (the white residue you sometimes find on dishes washed with aluminum cookware).– Adam DavisJun 25, 2011 at 19:05
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1So I can see that some knives would lose their edge with common dishwasher detergents. Using them on a plate, however, would dull them much faster anyway, so you might as well not worry about it. Buy new knives or sharpen the old ones as needed.– Adam DavisJun 25, 2011 at 19:06
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1Wood handles are also a problem in a dishwasher (like bone, apparently).– Craig StuntzJun 27, 2011 at 12:50
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1On top of the value proposition of possibly damaging an expensive blade that is easy to just rinse and wipe immediately, there is a safety issue. Knives are sharp. Dishwashers are full of awkward racks filled with dishes hiding what lies beneath them. If I make a rule to never put the knife in the dishwasher, I don't have to worry about getting cut by a knife when loading or unloading dishes. That said, I regularly put steak knives in the dishwasher, but loaded point down in the flatware basket to minimize the chance of impalement. The steak knives are not "quality" blades, though.– RBerteigAug 18, 2014 at 23:21
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2 Answers
Yes, knives get dull in the dishwasher, through rubbing against other items.
When I bought a set of nice Wüsthof-Trident kitchen knives, I heard this rumour too. I also heard that cutting onto a plate can dull them. As this was about 25 years ago, in the days before I had heard of the web, let alone a StackExchange, I wrote to my knives' manufacturer, Wüsthof, asking for advice.
They kindly sent me a brochure which has this section (my emphasis):
Caring for Fine Knives
- The best of edges will quickly dull if it strikes metal, glass or formica. A soft wood or plastic cutting board makes the best surface. And if a slip occurs, a proper cutting board is safer for the user.
- Knives should be used only for the purpose intended. Never use good cutlery to cut string or paper - it is an outrage to cut bones or metal with a good blade.
- Blades should never be heated in a flame in an oven. Elevated temperatures will destroy the temper of the steel.
- After use, knives should not be allowed to soak in water. The best practice is to hand wash and dry them immediately. This is especially true if they have been used on fruit or salty foods, which may cause some staining, even of stainless steel blades. Although Wusthof-Trident knives can be cycled in a dishwasher, it is not recommended. High water pressure will dull the cutting edges by knocking them again the rack and against other objects.
- Fine knives should be carefully stored in their own block, or special vinyl "roll" produced by Wusthof for this purpose.
Source: Wüsthof brochure, vintage ~1994. (I still have it, and can scan it in if required.)
I avoided putting them in the dishwasher, until I had a partner who refused to treat them with such respect. (To quote Wüsthof, it was an "outrage"!) For domestic harmony reasons, I got over it.
answered Jun 28, 2011 at 14:35
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16Reminds me of my house-mate who tossed their cutlery inside my non-stick pan to soak. tear– AlainJun 28, 2011 at 14:53
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2So if we secure the knives inside the dishwasher in a way that prevents it from being moved around (and thus smashing into things) would that negate the dulling effect? Jun 28, 2011 at 19:41
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7You should scan it. Not because I'm skeptical, but why not add it to the internets?– Borror0Jan 25, 2012 at 2:11
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2@Oddthinking I picked the knives over the girlfriend. I concur with Wüsthof, it was an outrage. May 18, 2017 at 10:41
Chef's Choice notes that the environment in a dishwasher would cause metals of different electronegativity to react (working principle of a battery), and that the force of the water may knock knifes against other objects. I.e. it proposes at least two specific risks. However, for both mechanisms, the effect depends on other objects. A knife in a dishwasher on its own would be safe.
