Knife Tech

TECHNICAL DETAIL

BALANCE - The best knives have excellent balance; that is, a balance between the weight of the handle and the weight of the blade. The actual point of balance ought to be on the blade, just in front of the handle, and can be tested by balancing the knife on a finger in that position. The latest development is a range of knives on which the balance can be ‘tuned’ to suit the individual user: the handle houses a removable shaft to which extra weights can be added on and from which they can be removed.

CORROSION - Modern stainless steel knives are highly corrosion resistant. Older knives made of carbon steel may discolour badly, particularly when in contact with acidic foods like lemons, onions and so on. Carbon steel knife blades may also rust if they are not dried promptly after washing.

DISCOLOURATION - While stainless steel knives are highly resistant to discolouration, it may occur if the knife has been exposed to a naked flame or other heat source. Also, some detergents may produce a bluish film – although this can usually be removed. More seriously, brown or black discolouration can signify the early stages of rust or corrosion, which usually indicates a lack of care in keeping the blade clean and dry and is attributable to prolonged exposure to acidic food, salts or detergents, steam from a dishwasher, etc, which can induce rusting and corrosion. At an early stage, this can usually be rectified by washing or scrubbing with a mild abrasive. Alternatively, there are various proprietary stainless steel cleaners available. If left to persist, discolouration can result in pitting and cracking of the stainless steel.

DISHWASHERS - Individual manufacturers should state whether a particular range of knives is dishwasher-safe or not. Instructions to avoid dishwashers could mean that the handles are not dishwasher safe, but many manufacturers also advise that knife blades are susceptible to corrosion if exposed for too long to the damp, steamy atmosphere of a dishwasher, and may also be damaged by contact with other items in the dishwasher. It is safer and better to wash and dry quality knives by hand immediately after use. Wooden handles in particular are unlikely to be dishwasher-safe, as they can warp and split.

DUCTILITY - The capacity of a metal to stretch, bend or spread when put under stress. If a stainless steel knife blade has good ductility, it is less likely to break or chip in use.

FACE SHARPENING - This refers to the Japanese practice of grinding the entire width of the blade at a steep angle to provide a sharp edge, as opposed to the European tradition of grinding just the cutting edge at a less steep angle.

FLEXIBILITY - Different knives need different degrees of flexibility. A filleting knife, ham slicer or a palette knife depend on being highly flexible to function properly; a cook’s knife or a cleaver need to be extremely stiff.

FLUTED BLADE - A knife with a long blade that has a plain edge and a series of indentations ground into one side of the blade or both, in which case they are staggered for strength. Each indentation creates a tiny air pocket between the blade and the food being cut, reducing friction and sticking and making for easy cutting of thin, even slices of cheese, cold meats, smoked salmon and pâtés.

HANDLES - Handles are available in a variety of materials. Plastic handles are popularly of polypropylene, which is one of the lightest and more inexpensive plastics, or, for a longer-lasting handle that gives a good grip, polyoxymethylene (POM). Polycarbonate is an almost unbreakable plastic alternative. Plastic handles can be moulded in one piece to slot over the tang, or in two pieces to be riveted either side of the tang. Wooden handles require more care than others, and are unlikely to be dishwasher proof as they can split and crack. An alternative is wood/plastic composite, which requires little maintenance, is hygienic and looks and feels like wood. Knives can also have stainless steel handles, which are welded onto the tang, and can feature indentations to improve grip. The shape and weight of a knife’s handle should also be taken into account as they contribute to the comfort and balance of the knife when in use.

HARDENING - A process in which steel is first heated to a very high temperature, then quenched in oil or water to reduce the temperature very rapidly. This process converts the microstructure of the steel from a uniform grain called pearlite to a fine, needlelike grain structure called martensite – and in the process it makes the steel harder, and thus able to maintain a sharper edge for longer. Hardness is measured on the Rockwell scale: good quality knife blades are typically hardened to between 55 Rockwell and 62 Rockwell.

HOLLOW GROUND BLADE - The result of grinding the blade by passing the cutting edge between two rotating grinding wheels. This produces a slightly concave blade section with a sharp point. The edge may be finished with a plain edge, or in the case of bread knives and tomato knives etc, be given a serrated or scalloped edge. These types of blades tend to be mass produced and are mainly suitable for lighter cutting and slicing tasks.

HOLLOW HANDLE - This generally refers to a handle made of stainless steel in two halves and either joined to the blade internally or externally. If the handle is left hollow, it may be too light to balance the weight of the blade; in which case metal weights or sand can be added inside the handle to provide perfect balance.

ICE TEMPERING - A special process during the hardening of knives, where the metal blade, after being heated, is quenched in sub-zero temperature, which produces an extra-hard blade which can subsequently be sharpened to perform to a very high standard.

MOHS - A measure of hardness, based on the ability of a hard mineral to scratch a softer one. The lead in a pencil has a Mohs hardness of about 1; a diamond is 10.

MOULDED HANDLE - A type of plastic knife handle that fits over either a neb tang or a whittle tang. It can be moulded with a slot, into which either type of tang can be inserted, or the handle can be moulded directly around a whittle tang.

NEB TANG - A type of tang that supports a moulded plastic handle. The handle is moulded to incorporate a slot. The tang is then inserted into the slot and secured firmly in position with rivets.

PLAIN EDGE - A plain blade edge without scallops or serrations. Plain edge knives require frequent sharpening to maintain the edge – sharpening ‘little and often’ is far better than letting the knife get blunt and then having to create a new edge from scratch.

RIVETS - Rivets are a type of metal pin used to permanently secure the knife handle to the tang. They should be fIxed so that they are flush with the handle, and tight fitting for hygiene. Knives made this way are described as having ‘riveted construction’.

SCALLOPED EDGE KNIFE - Usually a long blade, and made of very hard stainless steel, so reducing the need for frequent sharpening. It’s used for cutting bread, or other foods which are hard or crusty on the outside. Scalloped edge blades can be used to cut the same foods as fluted blades. The points of the scallops guard against the sharpness of the scallop curves. They cannot be easily sharpened using a steel, because the scallops need to be sharpened individually – but they stay sharp for a long time.

SEAMLESS CONSTRUCTION - Where metal parts are welded together, modern manufacturing techniques make it possible for the join to be invisible. Typically, this refers to the join between the two halves of the hollow handle, or between the handle, bolster and blade.

STAMPED BLADE - This is the alternative to a forged blade. The shape of the blade is stamped straight out of cold rolled steel, heat treated, and then ground, polished and sharpened. This is the process used to make most budget-price knives.

STRAIGHT  EDGE BLADE - A blade with no indentations or serrations, which gives a smooth, clean cut. Knives with straight edge blades can be used for carving meat, cutting fruit and chopping vegetables.  Also referred to as a ‘plain edge’.

STRIP GROUND BLADE - Made from a strip of steel, this differs from a taper ground blade in being thinner and having a flat profile. It is lighter than taper ground and not as strong, especially where the blade meets the handle. Strip ground blades can be extremely sharp, however.

TAPER GROUND  - Arguably the finest of all types of blade – machine ground all over to produce a gradual taper from the spine down to the edge, and from the handle to the tip of the blade. Taper ground blades are extremely strong, and provide excellent balance for chopping and general-purpose slicing. The taper also allows the blade to slice easily through food.

TEMPERING - Tempering is a heat treatment in which a knife blade is reheated to a temperature below its lower critical temperature. This rearranges the carbon atoms in the martensite in the steel, making it stronger, more ductile and malleable, and easier to machine.

WASHING AND DRYING KNIVES - Modern stainless steel knives are highly resistant to staining and corrosion, and need less care than their carbon steel predecessors. However, it is sensible to make a practice of always washing and drying kitchen knives as soon as they are done with, and then putting them away safely, rather than leaving them in a washing-up bowl or on a draining rack.

WEIGHT - A heavyweight knife has a satisfying, businesslike feel to it – but it is worth pointing out that for prolonged use, a lighter weight knife may be preferable in terms of strain. Also see Balance.

WELDED CONSTRUCTION - Most all-metal knifes which appear to be made from a single piece of steel are actually made in several pieces, welded together and ground and polished so that the welded joint is invisible.

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