The day you bought a dishwasher, you probably thought about stopping hand washing dishes, pots, cutlery and knives.
Not everything can or should go to the dishwasher, including the kitchen tool that you probably use every day: the knife.
It’s valuable, it’s expensive, and your dishwasher is slowly damaging it.
One of the most frequently asked questions by customers of quality and therefore also expensive kitchen knives is:
“Can I put the knife in the dishwasher?”
There are two schools of thought on this subject, those that hear the dishwasher destroying kitchen knives and those that say why not.
If washing the knife by hand is something that seems familiar to you, then you bought quality kitchen knives and read the material that accompanies them.
“Wash the knife only by hand, do not use dishwasher to wash your knives”
For all cutting items, including the knife the answer is NOT to put the knife in the dishwasher.
The problem is not the hot water that spoils the blades or handles because it would be necessary to reach much higher temperatures to affect the characteristics of the handle and let alone for the hardness and mechanical strength of the blade, it is not a hardening oven the dishwasher.
The main reason is corrosion.
For some years now, sodium hypochlorite (bleach-NAClO) has not been used to drink water worldwide, but chlorine dioxide (ClO2) which, as the temperature increases during washing, tends to turn into chloric acid (HClO3).
So-called stainless steel is actually oxidized.
In martensitic stainless steels used in cutlery, the introduction of chromium into the chemical composition, with a content of more than 12-13%, generates the phenomenon of passivation, i.e. the formation of a layer of transparent oxide on the surface that protects the underlying metal.
Chlorine ions (derived from chloric acid) are substances that manage to pierce this protective layer by triggering a phenomenon of point corrosion known as vaping or “pitting” that develops in depth and is particularly insidious.
In addition, the rivets present on many handles of knives are in some cases aluminum, reducing metal, creating the stack effect that tends to corrode in favor of the noblest ones present in the dishwasher.
Galvanic corrosion,theso-called stack effect occurs when two materials, chemically different, joined and put in contact with a conductive solution.
In the long run if you don’t heal the knives will tend to deteriorate.
Even some types of plastics of the handles will tend to fall apart/dry out losing elasticity and resistance with temperature changes.
For this I recommend you:
Wash the knife by hand, with a non-abrasive sponge and normal dishwashing detergent under running water.
Also useful to remove acidic substances during the use of the knife, such as lemon juice.
If you really do not want to give up the dishwasher, take care to remove the knives as soon as the washing is finished, drying them with a soft cloth.
For professionals it would be indicated the installation of a declorator upstream of the plant that reduces the amount of active chlorine in the water.
Corrosion is the main reason not to use the dishwasher to wash your knives.
Most kitchen knives are made of “stainless steel”, but is it really?
Stainless steels (or stainless steels from the inoxydable French, or Stainless Steel from English (“spotless” steel), or finally Rostfrei from German (without rust) are characterized by greater resistance to oxidation and corrosion, especially in wet air or fresh water, compared to so-called “carbon steels” (or common unre bound steel).
This capacity is mainly due to the near absence of carbon <=0.07%, and the presence of chromium, in the alloy, able to move, that is, to cover itself with a thin and adherent layer of oxides, practically invisible of the thickness equal to a few atomic layers (of the order of 0.3–5 nm), which superficially protects the metal or the underlying alloy, from the action of oxygen and external chemical agents. 
The minimum content of “free” chromium, i.e. not combined with carbon, so that a steel can be considered stainless is 10.5% so that it can have the formation of the “passive” oxide layer continuous and protective against corrosion. Chromium in the alloy, in fact, combining with carbon, can form chromium carbides that, precipitating at the edges of the grains of the crystal structure, limit its availability to form oxides and, therefore, to passivate. 
Values between 12 and 17% chromium are generally found in the alloy, but other elements can also be used in stainless steel to increase oxidation and corrosion resistance.
Most kitchen knives are made from semi-stainless steel to be more rust-resistant, but even the best rust-resistant steel falls prey to manufacturers’ processes, blade finishes, and more.
Water rich in chlorine and high-temperature chemicals increase the likelihood of damage.
With that damage comes the extreme probability that your customers call you complaining asking for the “guarantee” that accompanies your custom knife or the knives purchased if you are a retailer, from here it is important to understand that clear indications must be provided based on the steel and materials of the handle used on the clear advise of washing the knife in the dishwasher.
The materials of the knife and their construction
The construction of the knife will surely lead to the division between a knife that can get into the dishwasher and those that can not be washed in the dishwasher.
The choice of blade material is fundamental but the knife is made not only by the blade but also by the handle and the mechanical elements connecting the various elements.
If you use the dishwasher you need to know that some materials such as wood for handles is not suitable for that type of washing.
No matter what the wood is, it will lose its good looks and become opaque, it will begin to deteriorate.
If the handle is made of polymer it may be more suitable than wood but glued or riveted?
If it is glued, then it must not get into the dishwasher.
If one or more pieces of metal are welded again in this case avoid the dishwasher.
Whether the knife is completely metal depends on the material but are still quite unusual for kitchen knives but easier to see in cutlery.
So what to do?
Meanwhile, it is essential to know the material with which the knife is built both as blade steel and as a material of the handle.
This section if you know the material of your knife gives you advice.
Steels that are safe or that do not seem to have problems with the dishwasher are these but are not limited only to these:
Not influenced, but beware
It is not safe, better to avoid
You will have to stick to the fully metal construction, welded metal or riveted polymers.
Do not forget the higher the carbon, the greater the risk of rust.
When it comes to dishwashers, there are several models of dishwashers out there that have the ability to change the temperature, you will want to keep it around the temperature of 50-60 C or 122-131 F, it also starts with a kitchen knife, no one really uses them, to see how the knives will react.
Finally, be your person, don’t worry about what the Joneses are doing, no person or object is meant to be perfect, everything has stains and dents.
but… if you want japan’s high-carbon Damascus knives and their cleanliness is your Zen moment and you find inner peace, then do it, we won’t stand in your way.
What really happens to your knife during the washing cycle
First, there is the heat and humidity to deal with and your knife does not “appreciate” that condition.
The high temperature and humidity of the dishwasher can severely damage both steel and handle and is even worse if your blade is made of carbon steel (likely to rust) or has a wooden handle.
Don’t put the wooden spoon in the dishwasher, do you?.
Then in the dishwasher there is the turbulence that generates movement of the objects inside.
Water jets in the dishwasher can make the knife slam into anything else you have it with in the dishwasher and can damage the knife wire.
It’s a good way to quickly ruin a knife.
Ceramic knives run an even greater risk, because they are more fragile, and a cycle in the dishwasher can splinter the blade.
Then detergents are used, which can be as dangerous as the machine itself, causing the knives to mattify or discolour.
Finally, knives can damage items in the dishwasher as well as dangerous if you leave them with your tip up when you pick them up.
Point them down, they can damage tool baskets and point them upwards and risk injuring you.
If you really want to put your knives in the dishwasher, use dishwasher knife racks where you can store the blades safely and to protect the knives during the washing phases.
How should you wash your knives?
For most knives, hand washing in hot water and soap is fine, or even just in hot water.
Use hot water and only tap water, not boiling water.
Sometimes, if necessary use soap and if you know that you will not use them for weeks pass a layer of knife oil.
The best way to dry
Using a cotton towel is better than air-drying.
It is strongly recommended to dry a knife and then immediately put it back in its storage space, since letting a knife dry in the air allows the water to stay on the blade longer and offers the opportunity to damage the blade as it is left out.
“Letting water rest on the blade can cause oxidation or rust, even if a knife is made of stainless steel.”
We disapprove of the dishwasher because knives can develop stains from chemicals, they suffer damage from the tinkling of other cutlery and the vanity of being the person who does what he can and washes his hands.
This is based on personal and technical experience in the world of cutlery which is always being refined and should not be taken as a fixed rule but my advice is not to wash knives in the dishwasher..
That is my opinion and I think it is welcomed by most knife makers and builders although it can be convenient to wash the knife in the dishwasher and if you really want to do it is better to use the most suitable materials.
Are you experience?
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