Take the 2-minute tour ×
Seasoned Advice is a question and answer site for professional and amateur chefs. It's 100% free, no registration required.

When I steam green vegetables, like broccoli, they come out bright green. A few minutes later though, and they have darkened and dulled. Is this a symptom of cooking them for too long or is there some other way to preserve the bright green color?

share|improve this question
    
I didn't tried it myself, but I've read that you can add a bit of baking soda when boiling green vegetables, so they'll maintain their colour better. I have not idea if this also applies to other-coloured veggies. –  Mien Oct 11 '11 at 13:55
add comment

2 Answers

up vote 20 down vote accepted

Typically, vegetables will lose their colour if they are over-cooked, so it's probably worthwhile cooking them for a shorter period of time.

Usually steaming is a great way to preserve the nutrients and colour of vegetables, as is stir-frying rapidly.

Different kinds of vegetables contain various pigments in their skins. Green vegetables contain chlorophyll; red and white vegetables contain flavonoids; orange vegetables contain keratin. Each of these pigments requires a different approach when cooking to preserve colour.

When cooking green vegetables, never add an acid, such as lemon juice or vinegar, as this will cause the vegetables to discolour quickly. Always cook green vegetables rapidly and preferably without a lid.

With red and white vegetables, which contain flavonoids, the converse to green vegetables is true. Adding an acid during the cooking process will retain and even restore the colour. For red vegetables use a red or white wind vinegar. For white vegetables use a slice of lemon.

Orange vegetables, which contain keratin and are generally fairly robust, for the most part can be cooked with or without the addition of an acid, and they will usually retain their colour.

Another way to preserve the colour is to blanch the vegetable in boiling water for a minute or so, then plunge them into ice water. Doing this stops the cooking process instantly. Using the method is useful if you intend to freeze vegetables.

share|improve this answer
add comment

you need a big pot of water to blanch small amount of vegetable, small portion at a time.

theoretical background:

  1. there is gas in the immediate layer of the vegetable, which makes the vegetable appear a little bit dull. you want to drive this gas out.
  2. the color is provided by chlorophyll, which is destroyed by heat, acidity and vegetable enzymes.
  3. the enzymes works at room temperature, works quicker when slightly above room temperature, doubling their speed for every 10 degree C elevation of temperature, but is quickly deactivated (thus, become non-functional) at temperature near boiling point
  4. the acid is released into the cooking solution, and the action of acid is dependent on the concentration of acid.
  5. when temperature goes to near freezing point, all reaction slows tremendously

thus, use large amount of water and small amount of vegetable, then stop the cooking by quenching the reaction using ice cold water:

  1. the large amount of water relative to the vegetable ensures the constant boiling-point temperature of the blanching water - this ensures fast cooking with little time for enzymes to work. if you use too much vegetable at a time then the temperature will drop due to transfer of heat from water to vegetable. this allow (1) driving out of gas quickly, (2) cooking of vegetable quickly without yellowing (caused by degradation of chlorophyll), (3) quick deactivation of vegetable enzymes
  2. the large amount of water allows quick dilution of acid released from the vegetables
  3. when you see the much-needed green colour you want, you want to stop the cooking process immediately to "freeze the moment" and what you want to do is to let the ice cold water stop the cooking reaction from outside to inside (especially outside, since color's on the outside)

that's basically it

share|improve this answer
1  
The main problem with this approach is that it isn't appropriate if the plan is to eat the vegetables hot as they are now cold. –  Ryan Elkins Jul 11 '10 at 22:02
    
@Ryan, this allows you to pre prepare a large amount of vegetables without them losing their colour. As by the end they are now cooked, but cold, you can then reheat them at serving time either by dunking in a large pot of boiling water for a few seconds or by warming in a pan with butter, or however for how you want to serve them. Dunking in cold water might not be appropriate if you are only serving a few people and can cook all the veg at the same time (remember, blanch in small potions), but if you can't (or want to prepare them in advance) then this approach will solve your problem –  Sam Holder Jul 14 '10 at 7:14
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.