Keeping greens green (chlorophyll)
Also searched as: colour of green vegetables, olive-green vegetables, grey broccoli, keeping vegetables green
In short: The green in vegetables is chlorophyll. Heat and acid turn it into an olive-brown pigment. Short cooking keeps it bright.
Like a light bulb on a timer: in the first minutes the green even glows brighter, then it gets duller with every minute.
Simplified model
What happens
In the first minutes in hot water, green vegetables even turn brighter, because air escapes from the tissue. As cooking goes on, leak out of the cells and turn chlorophyll into an olive-brown pigment. in the water neutralises the acid and keeps the green, but destroys vitamins and makes the vegetables mushy.
Why it matters
Explains why beans in a stew turn grey and why restaurants vegetables and plunge them into iced water.
Rules of thumb
- Cook briefly in plenty of rapidly boiling salted water.
- Plunge into iced water straight away so it does not .
- Add lemon or vinegar only just before serving.
- No baking soda in the cooking water: it keeps the green, but makes the vegetables mushy and destroys vitamins.
Levers
3
“Cooking with the lid on keeps vegetables green.” Rather the opposite: without a lid, volatile acids can escape. But short cooking times and plenty of water matter more.
In practice
1
Vegetables
Beans, peas, broccoli: blanch, refresh, and mix with sauce only when serving.
Sources · 2
- Education Bureau Hong Kong: STEM – Fruits and Vegetables
- Harold McGee: On Food and Cooking (2004), Kapitel Gemüse, Eier