Kale

Kale keeps 5–7 days refrigerated — a little longer than most greens, and it can be pushed further.

Store it unwashed in the crisper, loosely bagged with a paper towel to absorb condensation. If it is a bunch with thick stems, standing it in a jar with an inch of water and a bag over the leaves keeps it crisp for well over a week.

Keep it away from apples, bananas, and other ethylene producers; kale yellows quickly on exposure.

If you wash kale in advance, dry it very thoroughly in a salad spinner. Wet kale slimes within days.

Kale freezes well once blanched, for about 12 months, and freezes acceptably even unblanched if you are using it in smoothies within a month or two.

Kale outlasts lettuce and spinach by several days, and the reason is structural. It is a brassica with thick, fibrous, waxy leaves rather than the thin, delicate ones of a salad green. That heavier cuticle limits water loss and physically resists the bacteria that turn tender greens to slime.

The tradeoff is toughness, which is why kale benefits from massaging or cooking while lettuce does not.

Being a brassica, kale contains glucosinolates, the sulfur compounds responsible for its slightly bitter, peppery character. As the leaves age those break down and the bitterness increases — an elderly bunch of kale tastes noticeably harsher than a fresh one. Frost, incidentally, has the opposite effect: cold weather causes kale to convert starch to sugar as antifreeze, which is why winter kale is sweeter.

Yellowing is chlorophyll degradation, accelerated by ethylene and warmth. Yellow leaves are safe but tired.

As with all leafy greens, there is a genuine E. coli and Salmonella consideration, since kale is grown close to the ground and often eaten raw. Wash loose kale thoroughly; do not re-wash pre-washed bagged product.

Discard leaves that are slimy, blackened, or wet and collapsed.