Why does spinach shrink so much when you cook it?

Every cook has done it once: a carrier bag of spinach, a pan piled like a haystack, and two minutes later a sad green puddle that would barely cover a slice of toast. Nothing went wrong. That is simply what spinach does.

Why it collapses

Raw spinach is overwhelmingly water. Wikipedia's spinach entry, drawing on standard food composition data, puts raw spinach at about 91% water. The leaves are thin and tender, with nothing woody to hold them up, so as soon as they warm through they go limp and the water runs out into the pan. What is left is the same amount of leaf, just without the air and the water that made it look like a lot.

Sturdier greens such as chard or cavolo nero shrink too, but less dramatically, because they have stems and thicker leaves. Our page comparing chard, spinach and cavolo nero goes into how each one behaves.

How much to buy

Think in pans, not portions. As a rough guide, a large bag of loose leaves cooks down to something closer to a side dish for two than a mountain for a crowd. If spinach is the main event, say tossed through pasta or spooned under eggs, buy what looks like too much, then a bit more. Spinach that is left over the next day is never a problem; it goes into a frittata, a soup or a pan of beans.

Baby spinach shrinks in the same way, it just cooks even faster. Mature, bunched spinach with stems has more to bite on and holds a little more shape.

Cooking it so it stays bright

The goal is green, glossy and seasoned, not grey and stewed. A few habits get you there:

• Wash it well and leave some water clinging. Spinach grows close to the ground and gritty leaves ruin a dish. The water left on the leaves is often all the liquid it needs to wilt.
• Use a big pan and add it in handfuls. Pile in a handful, turn it with tongs until it collapses, add the next. Crowding the whole bag in at once steams the bottom layer to mush while the top stays raw.
• Keep the heat brisk. A lively heat wilts the leaves quickly. Low heat lets them sit and stew in their own liquid.
• Stop early. Take it off the heat when the last leaves have just wilted. It keeps softening on the way to the plate.

Keeping it from going slimy

Sliminess comes from overcooking and from sitting in its own liquid. Two fixes:

• Drain and squeeze. Tip the wilted spinach into a sieve, press it with the back of a spoon or, once it is cool enough, squeeze it in your hands. You will be surprised how much water comes out.
• Dress it after draining. Return the squeezed spinach to a clean pan with olive oil or butter, a little garlic warmed until pale gold, salt and a squeeze of lemon. Now it absorbs flavour instead of floating in water.

This is the classic Italian route for spinaci ripassati: wilt, squeeze, then "pass again" through a pan of oil and garlic. It works for almost any tender green.

When to use it raw instead

If you want volume, use it raw. Young leaves make a fine salad with a sharp dressing, shaved Parmesan and toasted nuts. Raw leaves can also go into a bowl of hot pasta right at the end, where they wilt just enough without turning into a puddle.