Dull green vegetables

What turns them olive

The green is chlorophyll, and a magnesium atom sits at the centre of each molecule. Heat and acid together displace that magnesium and replace it with hydrogen, producing a compound that is a dull olive-brown.

Green vegetables contain their own acids, and cooking releases them. In a covered pan those acids concentrate in the steam and condense back onto the vegetables, which is why a lid is the single fastest way to lose the colour.

The process is not reversible, and it is not related to safety or to doneness — a dull green bean can be perfectly cooked and a bright one can be raw in the middle.

Keeping them bright

1. Cook them fast in a large volume of well-salted boiling water. Volume matters: a lot of water barely drops in temperature when the vegetables go in, so they cook quickly.
2. Leave the pan uncovered. This lets the volatile acids escape rather than condensing back onto the food, and it is the most effective single step.
3. Do not add anything acidic during cooking. Lemon, vinegar and tomato all go in at the end.
4. Cook briefly. Most green vegetables need two to five minutes.
5. Refresh in iced water the moment they are done if you are not serving immediately. This stops the cooking dead and locks in the colour.
6. Reheat in butter or oil rather than in water when you come to serve.
7. Season and dress at the table, not in the pan.

What helps, what does not

A large volume of water

Genuinely helps. The temperature recovers fast and the cooking is short.

Salt in the water

Helps slightly and seasons properly. Season the water heavily.

No lid

The most effective step. Acids escape instead of concentrating.

Iced water afterwards

Stops the cooking and preserves colour. Essential if serving later.

Bicarbonate of soda

Keeps the colour brilliantly and destroys the texture, turning vegetables mushy. Not worth it.

Steaming

Fine, and slightly worse for colour than a large pan of boiling water because the acids stay in the steam.

By vegetable

• Green beans and mangetout — two to four minutes, refreshed. The most dramatic before-and-after.
• Broccoli and purple sprouting — three to four minutes. Cut the stems thinner than the florets so they finish together.
• Peas — barely a minute from frozen. They are already blanched.
• Spinach — thirty seconds, then squeezed. It loses colour faster than anything else.
• Asparagus — two to four minutes depending on thickness.
• Cabbage and kale — a few minutes, and both are more forgiving than most.
• Herbs — never boiled. A five-second blanch and an ice bath if you need them green for a sauce.

Common questions