Why does washing knives in the dishwasher dull them?


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.

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.

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.

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.

Seeing as to how there are several different answers, and no one is able to come up with a definite conclusion, I’m gonna go out on a limb and say that this is most *certainly* an urban myth. Absolutely no one here has posted a single shred of credible evidence, and they’re all unsubstantiated claims. The sole blue link, as of writing, is nothing more than a knife’s edge under a microscope. No one here has anything better than “dude trust me”.

You may as well ask any random stranger on the side of the road to give their best guess. They’d probably give you an answer that sounds equally as plausible.



I had no idea that dishwashers dull knives. Is this a well known fact and I’ve been living under a rock?

It’s not the dishwasher as such, it’s that they can stay wet from some time allowing the very fine edge to ever so slightly pit from a type of rust, that’s the dulling that you experience, same effect if you leave them under other dishes on a washboard. Of course cutting hard things and a had chopping surface can do much more damage.

always best to hand wash, dry and put away knives after using them to keep the best edge possible

One possible theory I came across, even if your knife is immovable in the plastic tray, the water jets cause a slight difference in voltage between the knife and tub of the dishwasher which causes electrolytic corrosion right on the edge.

Again just a theory. The best sharp knife is a honing rod.

I’ve never heard a satisfactory answer to this. It always seems to be implied that it’s some effect of the water or the detergent or something, but in reality it always seems to come down to them banging into each other.

Which means that if you have a cutlery tray instead of basket, which keeps the knives upright and away from each other and anything else, it should be perfectly fine. IMHO a cutlery tray is far superior to a basket. I have one, always put all my knives (that are otherwise dishwasher proof) in it, and have never noticed any dulling.

To be honest the whole thing sounds like a myth to me. I think it’s probably fine to put your knives in the dishwasher, _especially_ if it has a cutlery tray.

I was always taught not to put knives on the racks as it would cut the coating and then the racks would rust.

Other than that, they’re fine.

I think there may be some cultural differences here because British dishwashers are quite different from American ones. I’m not sure if the presence of salt, the use of hot water (instead of heating cold water), the type of detergent, or the way the dishwasher dries matter, but all those things are different on each side of the Atlantic.

I don’t like washing my knives in the dishwasher because I’m worried about them rusting quickly. I wash and dry mine by hand