Knives in the dishwasher.
The day you bought a dishwasher, you probably thought about stopping washing dishes, pots, cutlery and knives by hand.
Not everything can or should go into the dishwasher, including the kitchen tool you probably use every day: the knife.
It’s valuable, it’s expensive, and your dishwasher is slowly damaging it.
One of the questions that is most frequently asked 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 topic, those that feel 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 purchased quality kitchen knives and read the material that accompanies them.
“Wash the knife only by hand, do not use dishwashers 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 concerns corrosion.
For some years now, sodium hypochlorite (bleach-NAClO) has no longer been used to purify water worldwide, but chlorine dioxide (ClO2) which, with increasing temperature during washing, tends to turn into chloric acid (HClO3).
The so-called stainless steel is actually very oxidizable.
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, that is, the formation of a layer of transparent oxide on the surface that protects the underlying metal.
Chlorine ions (deriving from chloric acid) are substances that are able to pierce this protective layer triggering a phenomenon of point corrosion known as pitting or “pitting” that develops in depth and is particularly insidious.
In addition, the rivets on many handles of knives are in some cases aluminum, reducing metal, creating the pile effect that tends to corrode in favor of the nobler 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 do not take care of the knives will tend to deteriorate.
Even some types of plastic handles will tend to flake / dry out losing elasticity and resistance with sudden changes in temperature.
That’s why I recommend:
- Wash the knife by hand, with a non-abrasive sponge and normal dishwashing detergent under running water.
- It is 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, the installation of a dechlorinator upstream of the plant that reduces the amount of active chlorine in the water would be indicated.
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 steel from French inoxydable, or Stainless Steel from English (steel “without stain”), or finally Rostfrei from German (without rust) are characterized by a greater resistance to oxidation and corrosion, especially in humid air or fresh water, compared to the so-called “carbon steels”(or common non-alloy steel).
This capacity is mainly due to the near absence of carbon <= 0.07%, and in the presence of chromium, in the alloy, able to passivate and that is to cover itself with a thin and adherent layer of oxides, practically invisible with a 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, for which a steel can be considered Stainless is 10.5% so that it is possible to have the formation of the “passivating” oxide layer continuous and protective against corrosion. The chromium in the alloy, in fact, combining with carbon, can form chromium carbides which, precipitating at the edges of the grains of the crystalline structure, limit their 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 cannot be washed in the dishwasher.
The choice of the material of the blade is fundamental but the knife is not only made by the blade but also by the handle and the mechanical elements connecting the various elements.
If you use the dishwasher you must know that some materials such as wood for the handles is not suitable for that type of washing.
No matter what the wood is, it will lose its beautiful appearance and become dull, it will begin to deteriorate.
If the handle is made of polymer can it be more suitable than wood but glued or riveted?
If it is glued, then then it should not get into the dishwasher.
If one or more pieces of metal are welded also in this case avoid the dishwasher.
Whether the knife is completely made of metal depends on the material but they are still quite unusual for kitchen knives but easier to see them 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 a tip.
The steels that are safe or that do not seem to have problems with the dishwasher are these but are not limited only to these:
|Sure||Not influenced, but be careful||Not safe, better to avoid|
You will have to stick to the all-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’ll want to keep it around the temperature of 50-60°C or 122-131°F, even start with a kitchen knife,no one really uses them, to see how the knives will react.
Finally, be your own person, do not worry about what the Jones are doing, no person or object is meant to be perfect, everything has stains and dents.
BUT… if you want Japanese Damascus knives with high carbon content and their cleaning is your zen moment and you find inner peace, then do it, we will not hinder you.
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 the steel and the handle, and it’s even worse if your blade is carbon steel (likely to rust) or has a wooden handle.
You 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.
Finally, knives can damage objects in the dishwasher as well as being dangerous if you leave them with the tip up when you go to get them.
Point them down, they can damage tool baskets and point them upwards and you risk injuring yourself.
If you really want to put your knives in the dishwasher use dishwasher knife holders 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 soapy water, or even just in hot water, is fine.
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 highly recommended to dry a knife and then immediately put it back in its storage space, since letting a knife air dry allows water to stay on the blade longer and provides an opportunity to damage the blade while it is left outside.
“Letting water rest on the blade can cause oxidation or rust, even if a knife is made of stainless steel.”
We disapprove of putting knives in the dishwasher because knives can develop stains from chemicals, suffer damage from the clinking 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..
This is my opinion and I believe that it is favorably received by most knife makers and manufacturers even if 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.
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