The knife and the dishwasher

The short answer fits in one sentence: a dishwasher dulls a blade, attacks its polish and loosens its handle. Here is why, point by point.

The heat

A normal cycle reaches 60 or 70 degrees, with a hotter drying phase still. That is not enough to undo the hardening of a steel, which happens at several hundred degrees, but it is enough to expand and contract a wooden handle glued to a metal tang. After a few dozen cycles, play appears.

The detergents

Dishwasher tablets are strongly alkaline and contain abrasive agents. On steel they dull the polish and encourage pitting corrosion, stainless included. On a wooden handle they slowly dissolve the finish.

The knocks

This is the most destructive factor, and the most overlooked. Throughout the cycle the basket vibrates. A blade ground at 15 degrees taps against forks, plates, the wall of the basket. Every contact chips a portion of an edge a few microns thick.

A knife comes out of a dishwasher blunter than it went in, even when it comes out gleaming.

The handle

Pakka wood is a stabilised composite, tougher than raw timber, but it stays sensitive to repeated hot-wet-dry cycles. The weak point is not the wood itself: it is the joint between handle and tang, where water eventually gets in.

The one case that does no harm

A knife whose blade and handle are a single piece of stainless steel, with no finely ground edge, wedged so that it touches nothing else. In other words: a table knife.

What to do instead

Rinse under warm water as soon as you are done, one drop of washing-up liquid on a non-abrasive sponge, from spine towards edge, rinse, dry immediately. The gesture takes ten seconds and it is the only difference between a blade that lasts ten years and one that lasts one.

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