No metal but stainless

What the guidance names

The problem tables list brass, iron, copper and zinc utensils as causes of dark or discolored pickles. The mechanism is straightforward: an acid solution held against those metals picks them up, and they change the color of the product. It is not a trace concern about a long exposure, it is a visible fault from ordinary contact.

It covers everything that touches it

Pots, spoons, skimmers, the tool you use to release air bubbles, the weight holding a ferment down, anything resting in brine for weeks. The failure usually comes from the item nobody counted as equipment: a brass skimmer borrowed for one batch, an old iron pot used once because the stainless one was in the sink.

One use is enough, which is why the practical form of the rule is to keep the wrong metals out of the room rather than out of the process. A rule that depends on remembering is a rule that fails on the busiest day.

What is fine

Stainless steel and glass, and food-grade plastic where it suits. For fermentation weights in particular, check the material rather than assuming, because a weight sits in acid brine for weeks and is the longest contact anything in the process has.

Where it shows up

As darkening, weeks or months later, long after the utensil has been forgotten. That delay is why this is worth fixing by buying the right equipment once rather than by being careful, and it is why the darkening page treats four of its five causes as purchasing decisions.

References