Why kitchen knives rust and what to do about it.


If you have a knife, you have not used for a long time. You might find it covered with rust. But thinking back, you realize that you had left clean and nicely wrapped. So how come your knife is still covered in rust? And what can you do to avoid and get rid of it?

The number one cause of rust is oxidation. Oxidation leads to corrosion, and corrosion is just another word for rust. This can appear anywhere and at any time. For oxidation to take place, it only needs iron to react with oxygen and water, and voila! You can remove it with lemon juice or even carbon soda.  

Probably one of the easiest misused pieces of equipment in the kitchen is kitchen knives, not only because they’re used the most, but more because most of the people don’t properly attend to their kitchen knives.
What I am trying to say is, most of the time, people fail to treat their knives with the care they need.

Using the dishwasher, tossing them in a drawer with all the other tools, and don’t keep them well enough sharpened. You see, all of the things I have mentioned above have one thing in common. They all lead to rust! I’m always surprised by how prone to rust knives are.

You’d think that a blade that cost more than $100, that can slice right through meat or cleave a squash in two would be pretty much invulnerable to any rust. Well, think again! All knives eventually will rust and inevitably dull over time, even if you do not use them. But there are ways to avoid rusting or get rid of them, and here is how.

If you are interested in checking out the best knives, you can find them here.

Why are my kitchen knives rusting?

Okay, we all know what rust is, but let’s see how and why this happens.
For metal to rust, three elements are required: water, oxygen, and iron.
Oxygen comes from the atmosphere and is everywhere. Iron is the primary element of steel blades, and finally, moisture (water), all of them combined, promotes the development of rust. Just so you know, it does not have to be liquid water, because humid air is more than enough to make knife rust.
If you can prevent these three elements from coming into contact, you have won! This doesn’t sound difficult, right?

Do some steels rust more easily than others?

The most common types of blade steel are Stainless Steel and Carbon steel. As the name implies, Carbon Steel is Steel with added carbon. Many steels can have different metal mixtures. However, it is the amount of carbon that makes the blade that plays the main role here. Most of the time, Carbon Steel knives contain around 0.5% to 1.5% carbon, which makes them very strong and long-lasting. Professional chefs prefer to work with Carbon Steel as it makes excellent survival knives. However, Carbon steel blades are unfortunately prone to corrosion if you don’t take proper care of it! They rust easily in a very humid and acidic environment. Stainless Steel blade, on the other hand, contains Chromium, which generally makes up between 12.5% and 13.5% of the blade. This creates a strong oxide coating on the exterior of the blade, which stops the steel from further oxidation. Thanks to this, the corrosion of the edge is decreased, which is why we call this ” Stainless.” Now, stainless does not mean stainPROOF, of course. They will, just like the rest, rust if you don’t maintain them properly, even if they take longer than Carbon steel ones.

Can you use a knife with rust on it?

First of all, you should always try to avoid having a rusty knife. Secondly, it’s easy to remove rust these days with alternative methods. But in case you do use it, a cut with a rusty blade has an increased risk of infection, because accidents may happen while you use the knife. So, you should not use a rusty blade in any circumstances.

Can rust permanently damage your knives over time?

If you have rust you must take care of it immidiately, it may begin to eat through the metal if neglected long enough, causing significant and permanent damage. If you have bought a knife for 100$, it would be a pity to see it rust away…

How do I keep my kitchen knives from rusting?

Keep your knife clean and dry.

Making sure your knife is cleaned correctly and dry is probably the first and foremost important thing to remember. You should try to make this as a habit even if your knife is stainless steel. Firstly, I would advise washing and wiping your knife between ingredients to limit cross-contamination. What I like to do is to wash the knife in the sink, then wipe it with a kitchen cloth.

Limit acids.

Compared to stainless steel, Carbon steel reacts to acid a lot faster. Probably at this moment, you’re thinking about all those citrus fruits and tomatoes you’ve been cutting, but I am sorry to say that even pyruvic acid that is found in onions count. When you cut something acidic, always wash the knife quickly and dry it right after. Ultimately, if you can let patina (which I will explain what this is later) build-up, your knife will be less sensitive over time. The one and only advice I can give is to simply use a stainless steel knife each time when cutting acidic foods each time.

Use Oil for storage.

You should never neglect Carbon steel knives. What mean by neglect is, you should always take care of them, especially if they are in a humid environment. In case you have too many to use, or if you in a damp place, consider wiping down the surface with a drop of oil.

What kind of oil do you use on a carbon steel knife?

When I said oil, it’s not just any oil, of course. You can use vegetable oil and whap your knife with plastic and send it to another country, for example. However, a coating of polymerized vegetable oil on your blade is not easy to clean off; You’ll need lots of soap and scrubbing. So you would want to avoid this problem. Instead, use traditional oil to store your knives. Tsubaki oil is a good choice. It’s sold in any store that is specialized in knives but also found online.

Catch rust early and clean it off.

Even if you took perfectly care and you maintained your knives, you will see rust someday. The reason? Humidity, humidity is something you cannot escape at least in some areas in the world. But no worries, it’s not the end of the world! You can simply remove rust especially if you catch it early on. 

Store them dry.

I think by now you got the point, always to keep your knives clean and dry. And the same thing, of course, is when you store them. Make sure to store them where it’s dry or at least someplace where water is not nearby. Even if it’s just a little splashed water, it can damage your knife over time.

Some other tips that help avoid rust on your knives.

  • Always wash your knives by hand with dish soap and dry them right away.
  • Don’t use harsh cleaning products.
  • Do not ever put knives in a dishwasher. The intense heat causes the metal to expand and contract, which causes stress points that later become the seed to rust.
  • Soaking your knives in water for too long is bad. Or letting them soak in soapy water, bleach solutions saltwater.
  • Spots such as watermarks can usually be wiped off effortlessly from knife blades, and for more tenacious rust stains, use a non-harsh metal cleaning paste or liquid – one made for stainless steel, and not a silver cleaner – if needed.
  • For rainbow-looking stains, simply use lemon juice.
  • If you can avoid saltwater, please do. If you must work in a saltwater environment, use titanium or ceramic knife instead.
  • Keep your knives always sharp. It is the best way to prevent pit corrosion on the cutting edge.

What is patina on a knife?

A Patina is a visible layer, which can have multiple colors that appear on the surface of your blade over time. It’s basically corrosion that makes your knife rust-proof in the long term. Patina can form naturally or can be forced onto the metal. Also a good explanation in this video below.

https://youtu.be/l2yVyhPqLKg

Does patina prevent rust?

Although rust and patina are both a form of corrosion, while rust destroys metal, patina protects it. Patina provides a protective covering to the metal by forming a thin layer. So this way, it prevents knife rusting but does not make it completely rustproof because it wears off through heavy use.

Building up patina.

Depending on what foods you cut, you may notice your carbon steel blade turns various shades of purple, blue, brown, grey, or even black. As long it’s not reddish or orange, you’re good! Certain types of food will help patina build faster, like cutting meat and or soaking your blade in blood (I know…it disgusting). Plantain coats actually hold tannic acid, the same active element you can find in those industrial rust converters that turn rust into that unreactive patina. You can force a patina in many ways, using warm vinegar, potatoes, or mustard, but these are the most common among many other options.

Should I force a patina on my knife?

There is no need to force the patina. It can develop by itself in time. I’ve seen it a few times and clearly noticed that natural patinas do look better than the forced ones. On the other hand, nothing is holding you back to clean up your knife immediately after use. In case you wish to see how it’s done, check the video below.

How to remove rust from carbon steel knife?

There are so many ways to remove rust. I have made a list of those I know of. But I almost sure that you will find other ways if you search online. The main thing to remember is trying to avoid (slow it down) rust is what you should be aiming for always.

  • Use a 3000 grit wet dry sandpaper. You can clean off the rust fast without scratching the knife’s surface.
  • Use a piece of daikon to rub on the knife. This is very common among sushi chefs.
  • Submerge an entire blade of your knife in a glass filled with enough vinegar. Let it sit for at least five minutes. Take it out and use a sponge to scrub away the rust.
  • Lemons are also a good option, cut one in two and rub it along the blade, then thoroughly rub the blade with a light(soft) cloth until you see the spots disappear. For extra cleaning power, you can drop the lemon in some sea salt and rub it again. The moment you see that the rust spots are gone, wash your knife with some (not too harsh) dish soap and dry it right away.
  • Brew a strong pot of cheap, pre-ground instant coffee. Let it sit till its cold. Find a cup deep enough to dip your blade in it. Use a sponge to put at the bottom of it and submerge your blade. To have the best effect, it needs to be submerged for 24hrs, but 8hrs should also do the trick depending on the rust. Take the knife out of the cup and wipe it with a damp cloth and dry thoroughly.
  • Plastic scourer with a baking soda paste seems to do the trick as well. With a little soda and water, simply rub it over the rust spot and then further rub it with a paper towel, this should remove the rust spot.
  • Stick the entirety of your blade into a potato (use two if needed) for a few hours and use a cloth and oil to wipe it, and you’ll be surprised with the results.
  • Onions have something called sulphonic acids, and they are the key ingredients in getting your blade cleaned. You just simply saw back and forth into it, and the rust will slowly come off by itself. 
  • You can also try with an abrasive metal polish like Flitz or Barkeepers Friend (also makes a patina in addition to removing rust, which is perfect). Take a damp washcloth and sprinkle some of the powder sparingly onto the cloth and then simply rub the affected rusty areas.
  • WD-40 is perfect for larger knives, those you basically cannot submerge. Spray the blade with a spritz of WD-40 and use a 400 grit fine sandpaper to rub gently without touching the edge of the knife. Wipe it down afterward with a dry cloth.

There are many more extreme ways of getting rid of rust, like a sander or a grinder or even electrolysis, but to be honest with you, if your knives became this rusty, it’s probably time to throw them out and invest in a new set of kitchen knives.

What knives do not rust? Are there any?

Ceramic knives are the answer to this. Even though we are not talking about the same ceramic that’s used to make your coffee mug. The most popular ceramic for knives is zirconium oxide, also known as zirconia. It’s really hard — substantioaly harder than stainless steel or carbon steel. And it does not rust, nor does it absorb any smells.

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