Spinach

Spinach keeps 3–7 days refrigerated, at the short end for loose baby leaves and the longer end for bunched mature spinach.

Store it dry. Line a container with paper towels, add the leaves loosely, and put another towel on top — condensation is what turns a bag of spinach into slime. If it came in a clamshell, adding a paper towel to the box helps considerably.

Do not wash it until you use it, unless it is visibly gritty, in which case wash and dry it very thoroughly in a salad spinner before storing.

Keep it away from apples, bananas, and tomatoes. Leafy greens are strongly ethylene-sensitive and yellow quickly near them.

Spinach freezes well once blanched, for 10–12 months, and frozen spinach is genuinely good for cooked applications. Raw frozen spinach thaws to a wet mass.

Spinach leaves are thin, have very little cuticle, and have an enormous surface area for their weight — the same geometry that makes flounder the fastest-spoiling fish makes spinach the fastest-spoiling green.

They also respire quickly, consuming their own sugars and giving off moisture, which is why a sealed bag fills with condensation. That moisture on the leaf surface is what lets bacteria producing pectin-degrading enzymes break the tissue down into slime.

The yellowing you see is chlorophyll degrading, accelerated markedly by ethylene exposure and by warmth. Yellow leaves are safe but tired; slimy or blackened leaves should be discarded.

The safety dimension is significant and worth taking seriously. Leafy greens are one of the leading vehicles for foodborne illness in the US, having been implicated in repeated E. coli O157:H7 and Salmonella outbreaks. They grow low to the ground, are irrigated with water that can carry contamination, and are eaten raw with no kill step.

Pre-washed bagged spinach should not be washed again at home — studies consistently find that re-washing introduces more contamination from sinks and hands than it removes. Unwashed loose spinach should be washed thoroughly.