Knives in the dishwasher

Putting knives in the dishwasher,I’ve heard, dulls the blade, and for wooden handles can ruin the wood, anyone know?

Yes, you should never put knives in the dishwasher.
(We aren’t talking about dinner knives, but chef’s, butcher, paring, filet knives.) The blades do get dulled. Just wash in the sink with normal dish soap.

Wood handles will definitely get ruined as well, not after a few washes, but over time.

The issue here is simple environmental wear & tear. Ever find a piece of glass that has washed up on shore? Notice how the edges are all smoothed over? The constant action of the water washing over sharp edges does the same thing to knife blades.

Regular knife blades have a hardness of about 5.5, maybe a little less. Window glass comes in at about the same figure on the Mohs hardness scale.

Ever find a piece of driftwood washed up on shore? Well that wooden knife handle…

I guess you see where I’m going with this.

OK, hold up. I’d be much more willing to believe that glass gets rounded in the ocean due to all the rocks and sand, not the water so much. I can’t see how water alone would have a significant dulling effect on metal.

I have no beef with the part about the wood handles, but say I’ve got a decent set of J.A. Henckels knives with waterproof handles. I sharpen these every couple of months anyway. Somebody show me some evidence that washing them in the dishwasher is a bad idea.

I hope you are honing your knives on a steel between sharpening. BTW, how are you sharpening them? On a stone freehand or are you letting someone who knows what they are doing do it?

Henckels knives are a substantial investment and I dont understand why you need “proof” before taking simple steps to prolong their life and usefulness.

The Dishwasher will damage your knives. period.
Water will get in between the polycarbonate scales and the tang and start to rust it. (Stainless does not mean rust proof!!) Henckels in particular uses a higher carbon content for their blades which makes them more susceptible to water damage.
In addition, if you use high temperature settings, you risk altering the temper of the blade. Tempering is what gives steel its toughness-no temper=poor cutting, inability to hold an edge, dangerous knife.

The harsh detergents used in DW soap can pit carbon steel blades as well.

So just spend the minute to clean the blade in soapy water, dry it off, and store it properly. I prefer magnetic holders as they keep the knife exposed to air to keep them dry, help minimize chipping of the edge in the drawer against other utensils, are more convenient and safer as well.

I am a kitchen designer/former chef/former knife maker. I tell all my clients this and will stand by it.

I have to second the comment about sand here. Do you have any cites for water alone dulling sharp metal?

I was always under the impression that it wasn’t the water per se that damaged the knives, it was the fact that when you put knives in the dishwasher, you’re usually going to put them in the silverware bin with the other flatware. I figured it was the knives rubbing against other pieces of metal that damaged them.

I put my smaller Wustof knives in the dishwaher all the time, and here’s what I have found.

The steak knives, which seem to have a thinner blade, tend to get dinged up on occasion. The blade of these knives does not extend all the way through the handle and consequently, the handles have cracked at point where the bolt/rivet/screw goes throught the handle and blade.

The non-steak knives, which have a blade that extends all the way through the handle, seem to be sturdier and have not cracked at all.

Of course, the steak knives only cost a fraction of the full set and will probably be replaced at some time.

OK. All of that sounds much more likely than a simple “Water dulls metal.” For the record, I do wash my Henckels by hand, as I use them daily and can’t wait for the once-or-twice-a-week dishwasher cycle. I just wanted to know why it was a bad thing to put them in a dishwasher.

To further the hijack, when I sharpen them, I use the steel. What else should I be doing?

I agree that the major dulling factor is banging against the flatwear. I don’t like putting good knives in the sink either, they get banged up and it’s a safety hazard to have a really sharp knife where it might not be seen when you go to do the dishes. The best thing to do is wash the knife immediately when you’re done with it and put it away.

Interestingly, I just got splinters in my hand from handling a knife which had gone through the dishwasher too many times. The wood is totally falling apart and the utensil is ruined, leading me to my next question… How does one properly dispose of knives? You can’t just throw them in the trashcan and risk having a garbageman slice himself. Any suggestions?

Granted my statement was based only on observation, but lots of it. I spend a fair amount of time in the kitchen & use Asian cleavers almost exclusively. They are light weight & have very thin blades, allowing you to easily get them razor sharp when needed. On the rare occasions when I use my dishwasher, I never put them in the flatware basket. I lay them out flat on the top rack. They still manage to dull sooner than can be explained away by chopping shallots.

Does anybody own a rock tumbler? I never had one but if I remember correctly, they can polish rocks smooth in 24-48 hours. If the abrasion of sand & rocks in the ocean can polish the sharp edges of broken glass so smooth in a few days, I don’t think it’s much of a stretch to believe that a few weeks or months of dishwashing can accomplish the same thing on fairly thin, soft metal. The environment inside the dishwasher may be less abrasive, but it is still hostile.

[sub]By the way, I rarely use my dishwasher in the first place unless I am cleaning up after a dinner for 12. It just seems like a huge waste to run two major appliances (dishwasher & water heater) for 40 minutes to wash a handful of plates & forks that I can wash by hand in 10 minutes or less. I use the dishwasher as an air-drying rack.[/sub]

There are three types of metal alloy used in high quality cutlery today:

•All carbon steel
•High carbon stainless steel, sometimes called “no-stain steel”
•Very high carbon stainless steel

All carbon steel is the softest, and very high carbon stainless steel is the hardest. In the middle is high carbon stainless steel. All carbon steel was used for years in the making of cutlery. The problem is that it rusts and stains readily.

There is much more about the quality & composition of knives made from the three types of steel I mentioned above at the cutlery Q&A & some interesting details on wear & tear of the cutting edge at the giude to honing & sharpening.

I maintain that a few months of the harsh environment in the dishwasher can be equivalent to a few days of abrasion tumbling on the beach.


Wrap the knife blade in cardboard if you are worried. I would not be but maby I am a jerk.


The rock tumblers I have seen worked with water and some sort of fine grit. When I was a kid we made cheap rock tumblers with a coffee can sand and water that we would run around with and shake. So I think that it is the abrasive material sand grit ect. that dulls things not water.

I would hope that refuse collectors know the hazards of their job well enough to expect all kinds of hazardous objects in the trash they collect. Never the less I would put them into the recycle bin with the glass jars & metal cans. Sure there is a small amount of wood that shouldn’t be there, but when the men come to pick up your trash they’ll be glad you put the knives into the recycle bin along with the broken glass & sharp aliminum cans.

I agree with that statement, but still think that a few weeks or months of harsh dishwashing can have the same results as a few hours of abrasive polishing in a sandy/gritty environment like a tumbler or sandy beach.

What takes days in the ocean, takes weeks or months in the dishwasher- that’s all I’m saying.

Wait just a rock-tumbling minute. I just checked out the ingredients list of my liquid dishwashing detergent:

•Chlorine bleach
Sodium silicate

We need to get a chemist in here pronto. The word silicate suggest to me that this is an abrasive substance.