Quezi

Choose your knife! (photos by Lucy Boynton - CC-BY)

A knife might seem like a simple object, but its form results from hundreds of design decisions.

Does the knife need to cut things? The obvious answer is “yes”, but butter knives and putty knives are more for spreading than cutting. Nevertheless, most knives need a cutting blade.

A good kitchen knife has a steel blade with a very sharp edge. So sharp, in fact, that it will be blunted by being used to cut things, and therefore must be regularly sharpened using a sharpening stone or sharpening steel. A knife with a hardened blade never needs sharpening (nor can it be sharpened), but the blade will be thicker and not quite so sharp.

A knife may have serrations along its cutting edge—a regular pattern of ridges and valleys produced by grinding or with a laser. These make the knife cut better when using a sawing motion. Closely-spaced serrations and can help compensate for the reduced sharpness of a “never needs sharpening” blade. Slightly broader and more pointed serrations are good for cutting foods that cannot easily be cleaved. The serrations on the blade of a steak knife help to tear the fibers of the meat. A knife for cutting bread may have quite broad serrations, to help to cut the slices without applying much downward pressure which would squash the bread.

The curve of the blade is also important. If the blade is parallel to the handle, it won’t make a good table knife because a diner holds the knife at a slight angle to the plate and the knife would only make contact at the very end. Instead, the blade must be gently curved or angled. On the other hand, a curved blade is useless for scraping out the last of the contents from a jar, because it only makes contact with the glass at one point along its curve.

When a knife is held in one hand and the food in the other, as when peeling an apple, the angle of the blade is not so critical. A paring knife, used for peeling and cutting fruit and small vegetables, benefits from having a pointed tip to the blade. The tip is used to pierce the skin of a tomato to get the cut started without the risk of splitting the tomato and spraying its contents by applying pressure to start a cut with the main edge of the blade. A paring knife also benefits from having a sharp corner at the end of the blade closest to the handle. This corner is amazingly useful for removing small imperfections from fruit, or eyes from potatoes. For reasons I don’t understand, knives with this sharp corner are harder to find than they once were.

Not only must the blade cut the food, it must release it after the cut. A slice of bread or a wedge of apple will fall away from the blade easily, but some foods need a little help to break the surface tension and allow air to enter between the food and the knife. A row of dimples makes a big difference to the ease of slicing tomatoes, while a cheese knife benefits from having holes in the blade to allow air in from the other side. A small hole near the far end of the blade is useful for allowing large knives (such as those used for butchering meat) to be hung up between uses.

The back of the blade needs to be thick enough that you can comfortably guide the blade with an extended index finger, however a very cheap knife (manufactured by pressing rather than by machining) will be less comfortable to use because it won’t have this thick back of the blade.

A little asymmetry of the blade’s cross-section is not normally a problem, except when cutting hard items such as raw carrots. In that case, asymmetry (due, for example, to a blade with serrations on one edge only) will make it impossible to get a straight cut, because the blade will tend to follow a curve.

The knife handle must be large enough and thick enough for easy control, and smoothly shaped so that it is comfortable to hold. It should have plenty of weight, as this makes the knife easier to control, and should certainly have enough weight that the blade doesn’t touch the table when the knife is laid down. A knife that will be carried around (such as a camping knife) requires either a sheath or a blade that folds into its handle. It may benefit from a hole in the handle so that the knife may be attached to a lanyard or a belt.

A one-piece knife where the handle is made from the same material as the blade is easy to keep clean. Failing that, the handle must be attached without a gap in which grime would accumulate. The handle may be attached by rivets, clips or glue.

The knife should be heatproof so that the knife can be placed in the dishwasher. Some old bone-handled knives fail in this regard. However, despite the urban legend that they must always be hand-washed, many bone-handled knives are dishwasher-safe.

A traditional silver-plated blade will tarnish easily in the dishwasher, so the modern buyer always prefers a high-quality stainless steel knife, or perhaps even an expensive ceramic-bladed knife that doesn’t alter the taste of food in the (slight) way that a metal knife does.

Specialised knives include

• fish-knives (with a deep blade shaped to assist flaking of the fish) ,
• disposable knives made from plastic, or occasionally from wood for environmental reasons,
• the relatively blunt cutting edges of Splayds and cake forks,
• knives for chopping (which must have a heavy blade to carry the momentum of the chop deep into the object being chopped, and whose handles must have space to protect the fingers from hitting the chopping board), and
• knives with rounded ends for use by children