Arugula

Arugula keeps 3–5 days refrigerated and is among the most perishable greens you can buy — treat it as something to use quickly rather than stock.

Store it dry, in a container lined above and below with paper towels, in the crisper. Condensation is what destroys it, and the towels are doing real work.

Do not wash until use, and if you must, dry it exceptionally well.

Keep it away from ethylene producers. Arugula yellows fast.

Buy the bunched arugula with roots or stems attached where you can find it — it lasts noticeably longer than pre-washed bagged leaves, which have already been cut, washed, and handled.

Arugula does not freeze for salad use. It can be blitzed into pesto and frozen, which is a good use for a bag about to turn.

Arugula combines the worst features for shelf life: very thin leaves with almost no cuticle, a high surface-area-to-weight ratio, and a high respiration rate. It is a fast-growing plant harvested young, and it has developed none of the protective structure that keeps kale or cabbage going.

It is also, botanically, a brassica rather than a lettuce, which is where its pepperiness comes from — the same glucosinolate chemistry as mustard and horseradish. As the leaves age those compounds break down and the flavor turns from peppery to harshly bitter, so bitterness is a reasonable age indicator.

Wet leaves collapse quickly into slime as soft-rot bacteria break down the cell walls. Because the leaves are so thin, this progresses from a few dark spots to an unusable bag within a day.

The safety consideration is the same as for other leafy greens, and it is not trivial: arugula is grown close to the soil, eaten raw, and has been involved in E. coli and Salmonella recalls. Wash loose arugula well; do not re-wash pre-washed bagged product.

Discard when leaves are slimy, dark and translucent, or wet and collapsed. Scattered yellow leaves can be picked out and the rest used promptly.