Why does washing knives in the dishwasher dull them?
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In the dishwasher, high pressure sprays of water knock everhing asunder. Have you ever found a Tupperware lid on the opposite side of the dishwasher from where you placed it? This is why. During all this commotion, the blade can be struck by hard objects such as adjacent silverware, or even the wire wrach. These strikes will dull the blade.
The edges get bashed against things by the water jets. Plus some knives that aren’t stainless steel will rust. I have some cheap stainless steak knives that I’ve washed in the dishwasher a whole bunch of times, but they get put into the silverware basket so that they don’t hit anything.
Sharp knives narrow to a very thin and deceptively delicate edge. Knives which are in the dishwasher will be exposed to water jets from various directions which can cause them to shift in whatever is holding them, causing the blade to impact something that would dull the blade edge.
Beyond that, some dishwasher detergents contain actual abrasives. This fine grit when blown around the washer will help strip off food particles but will also slightly abrade the blade edge such that it becomes dull.
Corrosion is probably the quickest reason they dull, and the next reason is mechanical dulling from hitting objects or abrasives in the water. The thin edge will corrode first when submerged in water for a long time. Lemon juice will dull it even faster.
It’s the handles. Sure they can get dulled by banging around, but you can always sharpen them. The high temperatures are very bad for wooden or composite handles and will eventually cause them to split or break. (Okay you can always replace the handles, but that’s a lot harder than just sharpening.)
Most knives are fine in a dishwasher. Most “nice” ones suggest hand washing them to keep them in the best shape. I have a counter top dishwasher with a glass front, so I actually get to see what happens in there. For the most part…not much to worry about.
The stuff that is possibly bad for the knife (but not necessarily dulling the blade)-
* The dishwashers heat the water a lot. So you have whatever is in there in a vrey hot, and very wet environment for a long time. If the handles are made from wood or even epoxy, it’s not the best place for them to spend a ton of time if you want to keep them new.
* The detergent is pretty hardcore stuff. It literally will dissolve most of the foods that are in there in a single wash cycle. Again, not a great place for things with shiny finished handles, oiled wood or epoxy handles.
* The water gets sprayed usually by a spinning arm. The water jets can make things fall or move in there. In some cases things fall and hit the actual spinning arms and can be damaged, or kick up and damage something else. Honestly the risk isn’t really high, but there is a chance that something could get knocked into your knife and chip it, or damage the finish or the blade itself. Ideally you don’t want anything touching your cutting edge unless you are cutting it. You can’t really control that in the washer.
* Some dishwashers have an open heating element in the bottom of the washer. If things fall and touch it, they can melt or be damaged. I did kill one epoxy handle knife this way.
I hand wash almost all of my “nice knifes” and I have some that are 20 years old and still in great shape. I have other good ones that I put in the dishwasher. I think it is one of those things were for “best care” do it by hand, but it won’t be the end of the world if you put it in the dishwasher.
Honestly I don’t think it does. People say they get banged around but I think you’d hear if things were banging around enough to dull a knife.
I’d guess if it says not to put it in the dishwasher it’s because the handle or the adhesive in the handle can’t take the heat and water.
I’d love to see someone test this myth. Too bad the myth busters aren’t around anymore.
Putting your knives in the dishwasher do not dull them significantly compared to what you use them for. Water certainly takes years to wear anything down and any grit in the dish soap would wreck plate designs and cause more problems than it would be worth.
What you do is sharpen them regularly and handwash them. Not to keep them from getting dull but to keep someone from cutting themselves when emptying your machine.
This from 70 years in the restaurant business.
I put them in the dishwasher but I put them in the silverware basket in such a way that they can only bang around on the soft plastic. A little cutting board oil keeps the handles in good shape.
your dishwasher is an *insanely harsh environment*. you are literally sand-blasting your knife (cheap detergents contain sand as an abrasive agent) with the dishwashing detergent, which is also highly alkaline and corrosive, then you’re applying up to 180F heat to it after a water bath.
all of that is happening to the edge of a blade which is thinner than a human hair if properly sharp. you will notice it faster on thinner edges as thicker edges are more durable, and it depends on the type of steel and tempering.
side note: know how sometimes some glass will develop kind of a cloudy film over time? f it doesn’t wipe off with vinegar, that’s the glass literally dissolving in the alkaline environment. if it’s lead crystal, that’s just lead leaching out.
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