Ken’s Knife Knowledge

This page is here to provide you with some details about knives and scissors. Over the years I asked many of these questions myself but few people in the sharpening industry actually knew the correct answer. I hope you find this useful.

How a knife works

A sharp knife is easier to use and control, but have you ever wondered why?

A knife cuts using pressure and tearing actions created by a wedge with an edge. A sharp knife has a wedge shape that comes to an edge with little teeth created by the sharpening material.

The knife cuts using the high concentration of pressure created by the wedge shape of the blade. As you push the blade into the food, it crushes and splits the food. The narrower the edge, the higher the pressure created, the better the crushing action. A dull edge creates less concentration of pressure so you have to push harder to cut.

A knife also cuts by tearing the food as you draw the knife back and forth across the food in a sawing motion. A close look at a sharp knife would reveal little teeth at the edge that bite and tear into the food. As the knife goes dull, these teeth wear down and the tearing action is reduced.

Why a sharp knife is safer and easier to use than a dull knife

Research shows that you are more likely to cut yourself using a dull knife than when using a sharp knife. Sounds wrong, but it is true.

When a knife is sharp, the wedge shape and little teeth at the edge quickly bite into the food you are cutting. You need less force to start the cut, the knife is easier to control, and the knife stays in place when you start to apply pressure. Using light pressure combined with a sawing action, and a moderate grip on the food, you can quickly perform the desired cut.

A dull knife does not work as well. The dull knife requires more pressure because it does not bite into the food quickly. As you push the knife harder you need to hold the food tighter. With all this extra effort the knife is harder to control and more likely to slide off the food and into your hand. Because you are already using greater force when you cut yourself, it could be very bad.

Why does a knife go dull?

A knife is a tool that wears during use. We cannot avoid the knife wearing, but we can control the rate of wear.

The three primary causes of knife wear are the cutting board, handling and storage, and the food, in that order. We can control the first two, and live with the last.

The surface you are cutting on causes the greatest wear to the edge of the knife. The wear occurs when the knife makes contact with the surface after cutting through the food. The harder the cutting board, the faster the wear. This is why plastic and wood cutting boards are much better than metal pans, countertops, and china plates. The greater the force used to cut the food, the harder the knife hits the cutting board, the greater the wear. If the knife makes loud noises against the cutting board, try to use less pressure.

Handling and storage include using, cleaning, and storing the knife and it is the second highest wear category. The wear is caused by the edge contacting other items. After using the knife, put it down gently on its side, don’t toss it. When cleaning, use soapy water and a cloth or sponge. If you need to apply pressure to clean the side of the knife, first lay the knife flat against the side of the sink so your fingers cannot touch the edge. Storing the knife where is does not touch other utensils will save the edge. A knife block, tray, or protective sleeve will help tremendously.

Last is the food. Frozen food, dirty food, food in their containers, and bones cause the greatest wear to the knife.

Keeping a knife in good working order

A knife will not stay sharp forever but you can control how fast it goes dull.

Always use a plastic or wood cutting board. A cutting board is designed to give when the knife makes contact. The harder the surface you are cutting on, the faster the knife will go dull. Do not cut on metal pans, countertops, dinner plates, serving dishes, or china. All of these items will dull the knife quickly.

Cut food only. You should have knives for kitchen use only and other knives for general house use. If you use your kitchen knives to cut up cardboard boxes, trim brush, open bags of mulch, cut rope and such, they will never stay sharp very long.

Store them properly. Avoid your knives banging into other kitchen utensils where they will be nicked and banged around. A knife block, tray, or sleeve will avoid this.

Cut with the knife, do not scrape. After cutting up food on the cutting board, do not use the edge of the knife to scrape the food into a bowl. Flip the knife over and use the back edge. The edge of the knife will last 3-4 times longer doing this alone.

Use a “steel”. Misnamed a “sharpening steel”, this tool does not sharpen a knife, but keeps it in good working order before it goes dull. It does a good job when used regularly before the knife goes dull and is easy to use after you understand why you are using it.

What is the best knife for me?

What’s best for you is a balance between price, quality, your appreciation of the tool, and overall value. You can determine best by trial and error and a little education.

The three main criteria for choosing a knife should be:

  • Is it comfortable in your hand.
  • Is it the right knife for the job.
  • Is it reasonably sharp.

Comfort. Is the handle too big or too small for your hand, can you control the knife, how is the weight, can I keep a firm grip when using the knife, and is the balance right. Simply put, does the knife feel comfortable when you pick it up and use it. You are already doing this evaluation if you have several knives at home, but only like to use a few.

Right knife for the job. You don’t want to be using a 10 inch chefs knife to do the job of a boning knife. It is important to have a variety of knives to handle different jobs and we think that five knives is the minimum number of knives needed in your kitchen. The knives are a paring knife, general utility knife, chefs knife, slicing knife, and a bread knife. The first three will be used the most when preparing food.

Reasonably sharp. A knife will stay reasonably sharp if it is relatively thin, good quality metal, and well taken care of. Care is the biggest factor in keeping a knife sharp. If relatively thin the knife will work well, but if very thin it is easily damaged.

Your knife is dull. Now what?

If you use your knives, sooner or later they will be dull and need to sharpened. Knives have needed sharpening for centuries and there are hundreds of tools and equipment to help people sharpen their knives. You need to decide if you want to do the work, or pay somebody to do the work.

I can do this. Yes, you probably can. The first thing to realize is that it will take time and practice and more practice. You can probably put a basic working edge on your knives, but it is a skill that must be developed. The basic principle is to grind away on each side of the edge, using the same angle on both sides, until you come to a point. Doing this by hand can be slow but you may have better control; whereas, using electric machinery will be quicker and less forgiving. The key is practice, practice, practice regardless of what you are using.

Who do I pay? There are many places to have your knives sharpened but that does not mean they all do good work. Locations include grocery stores, gourmet shops, commercial knife sharpeners, and some of the premium knife retailers offer knife sharpening services. Finding a good knife sharpener will take some work, but is worth it in the long run. (That is why you are here.)

When to use a sharpening steel

The name “sharpening steel” is misleading. The metal rod does not actually sharpen a knife, it maintains the sharp edge. Once the knife is dull, the sharpening steel is of no use.

If you could look at the edge of a sharp knife under a microscope, you would see little teeth created by the sharpening stones used to sharpen the knife. These teeth are responsible for the tearing action that is part of how a knife cuts.

As you use the knife, these little teeth tend to bend over. What the sharpening steel does is straighten and put all the teeth back in line. If you do not straighten the little teeth periodically, they will bend over and break off and the knife will get dull. The only way to create the teeth again is to use sharpening stones and remove metal from the knife to create a new edge.

To determine if it is time to use the sharpening steel, you can do the following. Hold a knife with the edge upward and try to reflect light off of the edge. If the knife is sharp, there will be no reflection because the pointed edge does not reflect light. In areas where the knife is getting dull, you will start to see a shiny reflection. If the knife is already dull, you will see a shiny reflection all along the edge of the knife.

What you want to do is use the sharpening steel when the knife starts to wear and the little teeth are starting to bend over. You can tell when this is happening if you see small reflections in areas of wear along the edge. The reflections will first start to appear on the portions of the edge that receive the most wear.

How to use a sharpening steel

All of us have seen chefs using a sharpening steel with hands flying and the sound of metal singing. This is another example of somebody else making a task look simple because of a lot of practice.

The basic principle is the same for a professional chef as it is for you. Keep in mind that you are straightening out the little teeth along the edge that have started to bend over. This does not require much force, but does require that the knife be held at a proper angle against the steel. To do this, it is best to have the sharpening steel in a fixed position and then move the knife only. The following steps will help you to use the sharpening steel properly. Be sure your knife is clean.

  • Take a look at the edge of the knife and check for reflections that indicate that the little teeth are starting to bend over. You will be comparing the reflections before and after using the sharpening steel.
  • Put a non-slip pad or wet cloth on your countertop. Hold the sharpening steel with the handle straight up in the air and the end on the non-slip pad.
  • Start at the high end of the steel near the handle. Place the edge of your knife that is closest to the handle against the side of the steel. Hold the knife at about a 20-degree angle against the steel. (How close is a 20-degree angle? If you take the corner of a piece of paper and fold it over twice like you were making a paper airplane, that is about a 20 degree angle.)
  • What you are going to do is slide each side of the knife down the side of the steel while you are pulling the knife towards you so that you make contact along the full edge of the knife. Be sure to maintain the 20-degree angle while sliding the knife. The longer the knife, the quicker you will need to pull the knife towards you. Apply light pressure while sliding down the steel. Do one side of your knife and then the other. Do each side 5-10 times. Check the edge of the knife for reflections along the edge. The reflections should be gone or at least less. Repeat as necessary; but if the reflections do not get smaller then the knife is probably dull in those areas. Do not hit the counter with your knife!

Scissors

Scissors work by two blades passing against each other and pinching the item to be cut. The scissor blade is sharpened on one side only, and is flat on the other side. The two flat sides pass against each other and the edges cut. Both the angle of the sharpened edge and the strength of the metal it is constructed from determines how sharp the scissors are, how long the edge will last, and what it can cut.

Do not force the scissors to cut an item. If you have to use excessive force, such as using two hands, the scissors were probably never designed to cut that kind of item. You could also be trying to cut too much at once.

Be sure the item you are cutting is clean. If you cut an item which is dirty, little pieces of grit will be pinched between the blades and damage the edges. It will be like cutting little pieces of rock

Be sure to keep your scissors clean and dry. This is especially true after cutting wet items, such as flowers or foodstuffs. Keeping scissors dry will avoid corrosion which can damage the edge of the blades.