31

What is it about the dishwasher that harms knives?

The only reasons I've found are:

  • You could get cut... I personally have a greater change of getting cut by trying to wash them by hand.
  • The blades can damage the plastic-coated metal shelves... so I put them in the silverware-holder instead of on the rack (it's 100% plastic, no metal).
  • The blade could get nicked by being knocked into other silverware... so put the blade by itself in a section of the silverware-holder in the DW.
  • 2
    I definitely think nothing wooden should go in the dishwasher, b/c the wood will eventually crack. But what about knives with no wood? – JustRightMenus Jul 18 '10 at 19:19
  • 2
    I've never heard of anyone not putting knives in the dishwasher. I've always put them in and they're fine. – MGOwen Oct 5 '10 at 3:10
  • I agree with the heavily downvoted answer's claim that "Most of the answers here seem to be 'I think so'" with very little hard evidence. There are different types of steel that are used for knife making and they have different properties. If you want a really excellent resource on sharp knife blades look at scienceofsharp.wordpress.com which uses electron microscope images of knife blade edges. It isn't for the faint of heart. But if you want to have sharp knives it does a great deal to cast off knife superstitions. – John Robertson Nov 8 '16 at 14:58

12 Answers 12

17

Expensive knives can survive a trip through the dishwasher, but like others have mentioned, they can bump into things, end up with coatings of detergents and such, suffer damage to wood, etc. Why would you do that to an investment?

Cheaper knives will just straight out rust/corrode, even if you remove them and dry them right after the cycle. Yeah, you can scrub it off, but you're also losing metal from the blade, possibly starting rust in areas you can't dry, and generally degrading the knives.

  • 5
    Our kitchen knives have always been cheap knives, but I have never had any sort of corrosion or rust. I would expect cheap kitchen knives are made of something like 420JS steel, which is actually better at withstanding corrosion than steel that is used for more expensive knives (the tradeoff is that more expensive knives can hold an edge longer, 420JS is softer). – John Robertson Nov 8 '16 at 14:38
  • 1
    Old post, but other responses don't make it clear enough - If your knives don't have delicate handles (not limited to wood!), and you're careful, putting them into separate compartments should be ok enough. But most people just throw them in with their other silverware (either in the dishwasher or afterwards in a drawer) without regard for their edge. Sure there's a chance they may chip if you're not careful, but they will dull that way, especially if they're low-to-mid-tier knives. Source: I make and sharpen (and re-sharpen :/ ) pointy things. PSA: Most household knives are dull. – HammerN'Songs Dec 27 '18 at 22:42
  • Personally I find the whole "nice knife" thing to be just a fetish. Knives are knives. They're tools. Use them. Don't abuse them. Your local butcher is not likely to have a ridiculously expensive space-age steel knife. Your local cook isn't either. Get utilitarian and find a knife that can go in the dishwasher and be done with it. A fancy wood handle isn't going to make your cooking better, but it will make it non dishwasher safe. Plastic handles last longer than wooden ones. At home our everyday silverware has plastic handles, and the fancy silverware is all metal. Everything dishwasher safe. – hjf Dec 28 '18 at 13:42
26

Well even for knives with no wood, a dishwasher is a very hostile environment. The reason is primarily for the blades. If you have quality knives that you care for, and plan to keep for many years, then it's just not worth it. It's just too easy for a knife to be jostled around and bang into other knives or silverware and get nicked.

You mention that you have a greater chance of getting cut when washing by hand. Well, there's a trick to that.

The easiest and safest way to wash a knife by hand is to press it flat against the side of the sink, then use your sponge/scrubber on the exposed side of the knife. Repeat for the other side. This keeps your blade safe, because the edge never touches anything. It also keeps your sponges and hands from being slashed to pieces by the blade.

Dry it immediately with a dish towel, using a pinching swipe from bolster to tip from the back of the knife.

  • 10
    Main focus on cleaning any knife without getting cut is really as you write...from the back of the knife. I've never cut myself while cleaning my knives, the only people I know that have done that are very clumsy of just the "kind" of people that throw all the knives into the sink and grabs randomly into the deep with allot of bubbles on top of their water :) – cyberzed Jul 18 '10 at 19:47
6

The biggest reason I've heard is that the wood handles can't survive in there and still look good. It can still work, but you have to be vigilant to remove the knives immediately on completion of the wash cycle. And yes, it's true. My wood-handled knives are noticeably grayer than their newer brethren.

Our non-wood handled knives (those Wüsthof blades) go in the dishwasher with nary a worry.

6

I've heard that certain components of dishwasher detergents may actually be so agressive you run the risk of making your knives dull. I'm not an expert on metal <> cleaning agent interaction, though, so kindly don't take that as an absolute truth.

What I have observed is that just putting the knives in the dishwasher loosely (as you oftentimes have to do due to the length of the knives) tends to have them rolling about a bit during the cleaning process, which makes them bump into other (metallic) objects such as pots and pans. That will make them dull, and that is why I always wash my proper knives by hand.

  • 1
    I can't believe I'm answering to a really old question, but anyway... what you're describing is a non-issue. The incredibly remote chances of "chemicals" attacking your edge, and your knife "bumping" into metal things in the dishwasher are completely offst by the fact that you NEED TO HONE your knife EVERY TIME you're going to use it. – hjf Dec 28 '18 at 13:46
5

The easiest way to damage any metal edge is to expose it to water and chemicals for longer than necessary. When the water just sits on the blade, the corrosion causes the metal to flake off (at a microscopic level). Immediately wash and dry your knife after use, and it will last you the rest of your life with minimal damage. I have also heard of some folks brushing rubbing alcohol along the blade to help dissipate the water.

This goes for shaving razors as well.

  • 1
    There was a very interesting article on Lifehacker a while back about people who dried their disposable razors by running them backwards on jeans/a towel/their forearm - and their crappy disposable razors would last 6 months to a year in some instances. Anecdotally, since I got a few very good knives and have started drying them immediately after every use, they've retained their sharpness for an incredibly long time compared to before. – stephennmcdonald Aug 3 '10 at 15:11
  • 1
    @stephenmcdonald: Interesting article! Here's the link. I won't be leaving my knives in the drainboard any more. – Neil Fein Aug 23 '10 at 21:48
  • @stephennmcdonald, sounds like they've re-discovered stropping. – Mark May 20 '17 at 1:00
  • 1
    any "microscopic metal flake off" or corrosion WILL BE REMOVED the second you HONE your knife. Because you're honing your knifes before every use, right??? – hjf Dec 28 '18 at 13:47
4

Adding this answer to provide some (admittedly anecdotal) evidence:

I currently own a knife that was given to me by someone else. The previous owner regularly put this knife in the dishwasher. It is not a cheap knife, but from a well-regarded consumer brand (Zwilling-Henckels) I would guess it is of medium to good quality.

Two things have happened to this knife:

  1. On the handle, water got in between the tang and the resin scales. In time, there was a buildup of corrosion, which split the resin scales. enter image description here

  2. The blade itself has developed some pitting (difficult to see in the picture, it is mainly on the spine, more clear near the tip.) enter image description here

There was also some damage on the knife edge, but as the previous owner also used a cheap draw-through sharpener, it is more likely that that caused the edge damage (it required complete reprofiling)

Based on this, I feel sure that always cleaning my knives by hand is the best way to treat them well. (That, and not using cheap sharpeners)

3

The stainless steel used for edges is not the same kind of stainless steel that is used for pots and bowls; it can be hardened far better but is by far not as corrosion resistant. Look up 300 vs 400 series of stainless steels. No one would usually make a sharp knife out of 300 series unless they are making a dive knife.

Also, especially expensive knives are not always made out of stainless steel at all, there are plenty of examples made out of non-stainless carbon steels or so called semi-stainless alloys (for example D2 aka SKD11).

Some of the cheapest blades are the most corrosion proof.

Dishwasher chemistry is harmful to all of these.

Also, thermal cycling, especially if uneven, can cause things to warp; with some blade designs warping is very bad news since they will be difficult to straighten and difficult to sharpen cleanly while bent.

Of course, handles made with wood, lacquer, bone, horn... are not dishwasher proof anyway.

1

the heat and water absolutely destroy wood handles. i can't think of a faster way of ruining a good knife with a wood handle.

dishwashing agents also corrode metal - including stainless steel. i've had good knives get pitted from bits of dishwashing powder stuck to it. the problem is especially bad for carbon steel knives.

don't do it - wash by hand.

0

My knives have wooden handles which are not dishwasher friendly (the varnish has a habit of melting). I'm also suspicious of the effect of the rinse aid which seems to add a thin coating onto everything, which might not be good for the blades.

  • 2
    A thin coating? I would stop worrying about the blades, and worry about what on earth it is you're digesting! – Arafangion Oct 6 '10 at 13:47
0

I don't see any mention of the fact that the heat/cooling causes small amounts of expansion and contraction. Over time, this weakens the seals between the handle scales (plastic, wood, pakkawood, all of it) and will result in handle scales separating from the knife. Not the only reason, but worth including.

-1

Dishwashers will heat the blade to a temperature that changes the structure of the steel itself so it will not keep a sharp edge. It only takes one time in the dishwasher for this to happen so if yours has taken that trip through--too late. If your knife is brand new--just be hyper-vigilant that one ever puts it in.

  • 7
    Interesting, which structure do you mean? I know of different types of steel structure created by heating and cooling, such as martensitic vs. austenitic steel, but they are created by cooling the metal down white-hot to room temp. Are you saying that the 60 Celsius in the dishwasher are sufficient to change this? Or do you mean something else by "the structure of the steel itself", and what is it? – rumtscho Jul 11 '16 at 19:25
  • Changes in the iron structure require higher temperatures, so this isn't a reason for not putting knives in the dishwasher. – kiamlaluno Sep 23 '18 at 11:38
-1

I was taught not to put black handled utensils in the dishwasher. The reason? The handles lose their black luster and turn grayish. They lighten. Guess what? It's true.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.