Blanching: Keeping Vegetables Green

Why the green disappears

The green in vegetables is chlorophyll, and chlorophyll is vulnerable to heat and acid. Heating releases organic acids from the cells; those acids strip the magnesium out of the chlorophyll, and the colour shifts to olive and then yellow.

Knowing that, the technique writes itself: cook briefly, dilute the acid, and give the acid a way out.

Use plenty of water

At least five times the volume of the vegetables. Two reasons:

1. The water temperature drops less when the vegetables go in. In a small pot it takes much longer to return to the boil, and the vegetables cook that much more. 2. The acid coming out of the vegetables is diluted.

Leave the lid off

With the lid on, volatile organic acids condense and fall back into the water. Lid off and they escape. This rule applies specifically to green vegetables.

Salt it properly

Roughly 10g per litre. Salt in blanching water seasons, but it also narrows the osmotic gradient, so less of the vegetable's own substance leaches into the water. Skipping it is the most common reason Sigeumchi Namul or Kongnamul Muchim tastes flat.

What the ice bath is for

Drained vegetables keep cooking in their own residual heat. An ice bath stops that instantly. Arresting overcooking is the main purpose — preserving colour is a side effect.

• Squeeze the water out thoroughly. For a dressed side dish especially, leftover water makes the seasoning slide off and taste dilute.
• Do not leave them in longer than about 30 seconds, or flavour leaches into the water.

Times by vegetable

Do not blanch different vegetables together; they do not cook at the same rate.

• Spinach, chives, perilla leaf: 20–30 seconds. Out the moment the colour deepens.
• Bean sprouts: 3–4 minutes — long enough to lose their raw edge.
• Broccoli, asparagus: 2–3 minutes.
• Carrot, potato: 5 minutes or more, or use another method entirely.
• Courgette: 1 minute. Longer and it goes soft.

When to keep the water

• Discard it: for vegetables high in oxalic acid, like spinach, or anything with a raw bitterness.
• Keep it: bean sprout water is a broth as it stands. The water from blanching vegetables for Japchae can go into a soup.

When not to blanch at all

Blanching does not suit every vegetable. Watery, mild ones — aubergine, mushrooms, courgette — only take on water and lose flavour. Roast or sear those instead; see Browning and the Maillard reaction.