Why Do Knives Need Sharpening?

Loss of sharpness is a natural cycle of any sharp blade and sooner or later every knife will lose its edge and become blunt. Every blade must therefore be sharpened. 

Did you ever wonder why knives lose their sharpness? Why some knives need more TLC and more frequent sharpening? What can you do to make sharpness last longer?

The ability to keep an edge depends on the choice and treatment of the material a blade is made of. Naturally, we can do our own part by taking care of and maintaining the blade and using correct cutting and chopping techniques. 

The usual suspects for the loss of sharpness and the need for sharpening are:

  • General wear and tear: It’s normal that a knife wears during use and significant wear and tear will become visible only after many years of use.
  • Curling or rolling of the cutting edge: A lot of force is exerted on the edge of the blade, so it can roll over to either side. This is how the cutting edge most typically gets worn, but the curling and rolling can to a certain extend be fixed by using a honing rod.
  • Chipping: The edge can chip or break under pressure, mostly when it rams against hard materials. Microchips are a great factor in losing sharpness.
  • Corrosion: We often use knives in a wet and acidic environment in the kitchen. Even if it doesn’t show on the surface, corrosion still chips away at sharpness.

Cutting technique: A good cutting technique is your best bet to maintain that fine sharpness.

    The properties that tell us how long a knife will maintain its edge are: strength, toughness, resistance to wear and tear.

    👉 You can read more about these properties in the Introduction to the metallurgy of kitchen knives.

    Chemical composition and hence its mechanical properties play a big role in what the steel will be like:

    Strength
    The resistance of material to deformation which is directly linked to hardness of material. In a kitchen knife, this means that a hard knife will maintain its edge for longer because it won’t curl or roll or become serrated as quickly and easily as in a softer knife. However, extremely hard materials are also more likely to break and chip. One such example are ceramic knives which are very hard but they quickly break or shatter.

    Toughness
    The resistance of a knife to deforming, breaking, chipping and cracking. A very tough knife will respond to force with bending rather than with breaking. What we want from a kitchen knife is hardness complemented by enough toughness so that it doesn’t break if we accidentally bang it against a plate or sink.

      

    Resistance to wear and tear
    Resistance of a material to abrasion – this is linked to the duration of sharpness and the ease of resharpening the blade. Resistance to abrasion grows with the hardness of surface and depends on the content and distribution of carbides in steel. Resistance to wear and tear is an important trait that comes into its own when we cut through a highly abrasive material.

    Hardness and toughness are inversely correlated: the harder the steel, the less tough it is and thus more prone to breaking. Therefore, very hard steels can’t withstand cutting through very hard stuff, such as bones or coconuts, without getting damaged (part of the blade breaks or chips). 

    Sharpening largely depends on the type of steel and type of carbides the steel contains and less on the hardness of the material itself. Steels with many hard carbides are harder to sharpen, so an inexpensive stainless-steel knife with a low HRC value and low carbon content can be much harder to sharpen in comparison with a blade made of high carbon steel with HRC 60+. 

    The basics of kitchen knife care and maintenance:

    • Use a wooden, plastic or rubber cutting board. On no account don’t use them on glass, ceramics, marble or steel.
    • Don’t leave your knives in the sink. Wash each knife by hand.
    • Don’t wash your knives in the dishwasher. The heat can damage the handles, edges can chip, and humidity inside the dishwasher can corrode the blade.
    • After use, wash the knives and wipe them dry.
    • When not in use, blades should always be protected so they don’t come into contact with other kitchen utensils. We recommend using a magnetic rack, knife blocks, especially designed drawers or using protective sheaths or sayas made of wood or leather. 
    • A knife is a tool intended for specific use. Don’t use it for any other purpose: it’s not a can opener, screwdriver, trowel, wire cutter, hammer etc. Kitchen knives are meant for preparing food.
    • Use the right knife for the task at hand – a small paring knife intended for delicate work won’t do well if you’ll try to chop bones with it.

    So, how can we apply all the above in practice, when using our precious kitchen knives? A fact of the matter is that the duration of sharpness largely depends on whomever uses the knife or, in other words, whether they use and store the knife correctly. This means that whether a knife will remain sharp or not mostly depends on how it is treated and not so much on the quality of steel or sharpening method.

    And this is good news, right? After all, changing our behavior is one of the easiest things to do. 😀

    ← Older Post Newer Post →