My dishwasher-safe knife is rusting. Why is it rusting?

You've been looking for dishwasher-safe kitchen knives because you don't want to waste time washing them by hand - that's understandable! But surprise, after the first run in the dishwasher, rust marks appear... Why?

Knives contain carbon to be sharp

These corrosion marks are mainly due to the salts in the dishwasher. Even when described as machine-washable, knives are still made of steel, and no matter how stainless they are, knives must contain a lot of carbon to be sharp (which is not always the case in cutlery). And carbon is oxidizable! A knife made of so-called "stainless" steel is never 100% stainless!

Rust can occur at the level of the marking or engraving of the brand on the knife, simply because the surface is already "attacked", and the phenomenon of surface corrosion is then accentuated. However, this does not damage the knife's characteristics.

Contrary to popular belief, household dishwashers are harder on cutlery and knives than professional equipment: cycles are very long (sometimes over 2 hours), and at high temperatures (often 80°). And it's not the cheapest detergents that are the most aggressive - quite the contrary! Using "brand name" products is often good for glass, but often bad for steel.

Advice:

It's important to take the knives out at the end of the cycle to avoid leaving them in the damp atmosphere for too long. It's also advisable to dry them well immediately after washing (program the start at the end of the night to take them out in the morning, or during the day when you're present).

Avoid putting them in contact with other steels, such as utensils and cutlery (some cutlery trays in recent machines have separator compartments for blades, by the way).

If, despite all these precautions, brown spots appear, clean them before they turn to rust and attack the blade. A simple, slightly abrasive sponge will remove this surface corrosion.

Did you know?

The words "18%", "18/0" or "18/10" on cutlery mean that it contains 18% chromium. Chromium is the essential element that makes steel stainless. The French standard requires stainless steel to contain a minimum of 13% chromium for food contact.

The more Chromium, the less oxidizable it is, but the less Carbon it contains, which gives it its hardness!

That's why forks and spoons can contain a lot of Chromium (and even 10% Nickel in the case of 18/10), but knives have less, for sharpness.