KNIFE CARE FOR THE PROFESSIONAL
*Thanks to the Frosts/Mora company of Sweden for the following information*
To be able to get maximum usage as possible from your working tool and thereby make your working situation as easy as possible puts great demands on the properties which govern why a tool functions or does not function in different situations.
By attaining the right properties one also ensures the avoidance of extra stress on your body when working. To be able to cut with a sharp knife instead of a blunt knife when working in different cutting positions during a whole working day will mean that the total body stress will be greatly reduced.
It is of course important to understand how the cutting edge of the knife must be formed and how one keeps and maintains the sharpness in the best way.
A knife that repeatably or often cuts towards the bone must be able to withstand much heavier treatment than a knife which is only used for cutting and finishing operations.
This is the reason why knives for different operations must be sharpened at different cutting edge angles. This also means that the knives with different cutting edge angles demand that they must also be finished off using different angles when applying the sharpening steel.
Different knives are also in steels with different harnesses which means that there can be difficulties when sharpening. Here it is easier to note that a soft knife is easier to sharpen but at the same time the edge retention time will be shorter. This in turn will mean that the knife has to be resharpened more often which means that more working time will be spent keeping the knife sharp.
Knife sharpening is an art in the same way as cutting is an art and by learning as much as possible it is also possible to achieve greater satisfaction in his work.
Stainless steel knives for use in the food processing industry are of made of so called martensitic stainless steel which unlike the austenitic stainless steels can be hardened.
Knife steels contain between 0.4 to 0.7% Carbon and between 13 and 18% Chromium. Carbon is necessary to make the steel hardenable and Chromium to is present to prevent corrosion ie rust. In general it can be said that Carbon contents below 0.5% are not to be recommended for professional usage since it is not possible to achieve sufficient hardness. Such knives on the other hand have excellent corrosion resistance properties which may be more important in the kitchen where appearance of the knives is more important.
Frosts use almost solely steel from Sandvik with the Steel Grade Code 12 C 27. This steel contains 0.6% Carbon and 13.5% Chromium. This, together with a special hardening treatment using liquid Nitrogen at -80C, ensures that the knives achieve a hardness of between 57 - 58 Rockwell C. In comparison to other knives this is amongst the highest attainable hardness levels without affecting the sharpening ability to any marked degree.
Knife sharpening also demands that the the sharpening equipment is kept in good condition. All the knives must be carefully cleaned first prior to sharpening to prevent fat or meat particles becoming attached to the grinding wheel surface which would thereby cause detrimental effects when sharpening. This should be clear common sense but unfortunately it is not always the case.
All knife manufacturers recommend wet grinding when using grindstones since the risk of overheating of the cutting edge is reduced to a minimum. Grinding using a fast operating grinding belt puts great demands on the grinding operator. The slightest discoloring of the knife cutting edge indicates that one has reached temperatures that are detrimental to the steel. The results may well be lower hardness and micro cracks in thinner parts of the edge, both of which most certainly produce a poorer quality knife. One should therefore ensure that grinding should take place on a slow moving grindstone with good water cooling thus avoiding damages through overheating.
When grinding knives used for the finishing operations, the total grinding angle should be around 25 degrees. If this angle is less, whilst the knife will be extremely sharp, it will also mean that the knife condition will also be very sensitive since the extreme knife edge point will easily be folded over when coming in contact with harder objects. Boning knives on the other hand are ground to higher angle, approx 35 degrees and thereby up to tougher use and heavier work on the knife edge even though this is at the expense of a somewhat higher cutting resistance.
In both cases it can be good to make a honing angle on the top of the cutting edge and thereby strengthen it. This honing angle should be somewhat larger that the grinding angle. This effect can also be produced to a certain degree when polishing the cutting edge on a polishing cloth wheel due to the slight abrasive action of the polishing wax.
Some experienced professional knife users can produce this "extra" cutting angle by using a fine grinding stone and thereby produce knives that keep their sharpness for weeks merely by straightening up the cutting edge using a polishing steel or by honing occasionally. What mostly happens when a knife begins to become blunt is not due to pieces becoming removed from the cutting edge but instead is due to the edge "bending over" and thereby not cutting.
The sharpening steels have therefore the function to press the edge back into place a central position. It is therefore easy to understand why polishing steels are being more and more used. Coarser sharpening steels are really only used when standard grinding equipment is not available. It should however be noted that after sharpening with a coarse sharpening steel a polishing steel should always be used in order to even out the unevenness resulting from the coarser sharpening.
It should also be noted that both operations using the coarse sharpening steel and the polishing steel should be conducted as previously recommended, i.e. that the pressure of the knife against the steel be gradually reduced so that the last draw be very light. Just like a stroking operation of the knife edge.
The steeling angle shall be the same as the honing angle, i.e. not larger, so as to prevent the top of the cutting edge becoming rounded more than necessary. As mentioned before knives have different grinding angles depending on their applications. The angles used when using sharpening steels shall be the same as their respective original grinding angles. Carry out these operations carefully and slowly making sure that the light is good. Place the blade against the sharpening steel and lift it until the top of the edge meets the sharpening steel surface. This is then the correct sharpening angle to apply.
Remember that all sharpening operations for cutting tools builds around the fact that one progresses from coarse operations (grinding) to fine working (polishing). However if the cutting tool is not so worn then one does not need to regrind but instead just polish.
Finally, ensure that the grinding equipment is always emptied of water after the working day so that the grinding wheels do not become locally soaked through with the result that they become soft in these parts and become unevenly worn. Heavily dirty grinding wheels can be cleaned by using a strong fat dissolving cleaning agent or spirit.
Another tip to be used at the workplace where knife sterilization is carried out is to dry the knives carefully before placing them in the sterilizer and thereby prevent any protein burning firmly onto the knife blade during sterilization. Thus one can avoid that the knife becomes difficult to work with and thereby giving the impression that it is blunt.
Most users of sharpening steels today are of the opinion that using a polished sharpening steel is the best method to maintain the knife's sharpness. The exception to this is within the fish processing industry where tradition has been taken over from the fishing trawlers and where sharpening equipment was seldom available. In this industry the coarse surfaced sharpening steels have remained in much greater use than in the other food processing industries.
In order to learn how to "steel" knives one must understand what effect the sharpening steel has on the knife blade. With qualified sharpening, that is by using a sharpening steel with a polished or fine structured surface the task of the sharpening steel is to put pressure on the knife edge that has been somewhat bent over through contact with the harder grinding material.
Penetrating this question further and considering how the knife edge looks under the microscope one can see that it looks like an even sharp ridge. Using for example a coarse structured sharpening steel, would only result in tears and loose hanging steel particles i.e. raw edge. On the contrary when using a polishing steel this ridge would be smoothed out and the result would be an even uniform pointed edge.
The knife must be rested against the sharpening steel at exactly the same angle corresponding to cutting edge top angle. This angle between the sharpening steel and knife edge must be maintained all the while when drawing the knife from the back edge to the knife point. The pressure of the knife against the sharpening steel can be, if the knife cutting edge is very damaged, fairly heavy in order to press the damaged edge back to normal. The pressure should be gradually reduced throughout the sharpening operation so that the final draw is almost like a stroking with a feather. The most important thing to remember here is to have complete control over the complete operation and not to to use draws that have little or no effect on the cutting edge. It is not so important on how the "steeling" operation is carried out and how one holds the sharpening steel as long as one has complete control over the whole operation and not to exceed the grinding angle which will result in a rounding-off of the top of the cutting edge.
The knife edge must however be moved against the sharpening steel in a cutting movement. Both sides of the knife should be continually "steeled" alternatively followed by testing to test the sharpness.
Use both eyes and ears if at all possible. The eyes, in order to ensure that the sharpening angle is correct and maintained and the sound from the grinding operation which becomes gradually diminished as the knife edge becomes even and sharp.
It would often appear that the general idea is that the "steeling" operation shall be carried out as quickly as possible just like in a speed competition. This is only a result of an unfortunate attempt to impress on the people around and will only lead to unsureness for others who are trying to learn the correct ways of knife sharpening. Gradual and controlled movement are the very basic recommendations in order to learn how to sharpen to produce a sharp knife.
There is also absolutely no magnetic influence whatsoever on the knife edge or any other magic energy source that affects the finished result. The magnetism in the sharpening steel is only there to enable the collection of loose particles at the top of the knife edge which would otherwise damage the edge during sharpening.
Through training, consideration and thought most people can learn how to "steel" a knife to razor sharpness.
knife care information