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Preserving the Dark Green Color in Vegetables


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traditional thinking says that you briefly boil green veg (asparagus, broccoli, bok choy) in salted water then 'shock' them in ice water to rapidly cool then continue your cooking.

this is said to "fix' the chlolophyll and other pigments and prevent them from denaturing and turning yellow

in Keller's book Under Pressure he states they do not SV green veg as they do not retain their color.

as he's probably a bright guy or has a bright staff, the shocking system above probably does not work.

perhaps SV takes longer?

Id love to SV asparagus, bok choy, broccoli with a touch of appropriate 'sauce' and get it perfectly cooked but stay dark green

i dont have Modernist Cuisine (yet!) but what do they say? whats been your experience?

many thanks!

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traditional thinking says that you briefly boil green veg (asparagus, broccoli, bok choy) in salted water then 'shock' them in ice water to rapidly cool then continue your cooking.

this is said to "fix' the chlolophyll and other pigments and prevent them from denaturing and turning yellow

in Keller's book Under Pressure he states they do not SV green veg as they do not retain their color.

as he's probably a bright guy or has a bright staff, the shocking system above probably does not work.

perhaps SV takes longer?

Id love to SV asparagus, bok choy, broccoli with a touch of appropriate 'sauce' and get it perfectly cooked but stay dark green

i dont have Modernist Cuisine (yet!) but what do they say? whats been your experience?

many thanks!

According to McGee, "That wonderfully intense, bright green that develops within a few seconds of throwing vegetables into boiling water is a result of the sudden expansion and escape of gases trapped in the spaces between cells. Ordinarily, these microscopic air pockets cloud the color of the chloroplasts. When they collapse, we can see the pigments much more directly."

He then goes on to discuss the effects of enzymes and loss of the magnesium atom in chlorophyll and their relation to loss of color. He suggests using small amounts of baking soda in water with a pH lower than 7 and cooking the green vegetables in a large volume of water to dilute the acids inside the vegetable's cells.

Are you wanting to SV the vegetables with the sauce to "meld" the flavors? IMHO, I would just cook and toss in the sauce since I don't think an application like this would lead to a "better" end-product.

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In Keller's Under Pressure, he consistently cooks things for longer times and higher temperatures due to food safety concerns and publisher liability. (This overconcern issue is discussed at length in Modernist Cuisine.) I don't have UP, so I can't check what's in there, but the claim that all vegetables lose their green color in SV is a sweeping generalization that just isn't true. I do it all the time.

Chris Amirault

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Sir Luscious got gator belts and patty melts

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Here's an interesting side note on this question by the Ideas in Food chefs:

link

Anna Nielsen aka "Anna N"

...I just let people know about something I made for supper that they might enjoy, too. That's all it is. (Nigel Slater)

"Cooking is about doing the best with what you have . . . and succeeding." John Thorne

Our 2012 (Kerry Beal and me) Blog

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Thanks, Anna. I was just looking for that. The gist of it (in case the link breaks) is that cooking vegetables that have been vacuum-sealed by placing the bags into boiling water is a way to preserve color and flavor, one more effective than blanching.

Chris Amirault

eG Ethics Signatory

Sir Luscious got gator belts and patty melts

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Nice link. I'd interpret the conclusion slightly differently than Chris does. They were basically testing whether cooking them in the bag alters anything--they kept the cooking time and temperature the same for both the boiled and sous vide celery (4 minutes, 100C, cooled in 0C water). Their conclusion was that the flavor of the SV version was better because nothing was lost to the cooking water. Appearance-wise though, the two methods were very close ("both versions of celery retained a bright vibrant green color, although the sous vide celery seemed a shade brighter").

The link and McGee both say the trick to keeping green from turning to brown is to keep the cooking time short, which they do by cooking for 4min/100C. The bag is just helping the flavor.

Can I rephrase the question? Can you use SV to cook green veggies for longer times and lower temperatures (e.g., 185F) than traditional blanching and still keep them green?

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many thanks.

Ill try theses things very soon with asparagus, and dark green bok choy.

thanks again.

I had hoped with SV you could get the cooking "just right' by temp control, after all its very very easy to over cook asparagus and broccoli and completely ruin them.

making them in the bag might be the answer to that problem in the least.

I can almost never cook asparagus 'just right' and serve it hot if im making many other things at the same time. I cook it 'just right' first, ice bath it, then serve it at room temp with a sauce.

just my skill level for these three veg.

Odd Keller emphatically does not SV green veg.

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Wayyy at the bottom of this very long page mostly on nitamalization: http://www.cookingissues.com/2011/03/09/mesoamerican-miracle-megapost-tortillas-and-nixtamalization there is mention of uses of very small amounts of baking soda or calcium hydroxide to keep green veggies both green and firm in boiling water. What they indicate for quantities is a "pinch". Does anyone have any more exact proportion of cal to water?

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I have heard of the baking soda thing (at least i have if baking soda is another name for bicarbonate of soda - can someone confirm?) but I also heard that this destroys some of the vitamins. Don't shoot the messenger if this is bad science, but I would love to know if it's true.

Baking soda is the same as sodium bicarbonate, bicarbonate of soda, etc, etc. My understanding is that it does affect vitamins B1 (thiamine) and C.

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I am curious about the correct amount of calcium hydroxide to add to water to keep veggies green and firm. I didn't see any quantities mentioned in that link above other than a "pinch". Not knowing how much water that they used, and suspecting calcium hydroxide may be very strong stuff, I am looking for guidance on correct proportions so I get enough but don't accidentally create a vegetable environmental superfund site.

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  • 5 months later...

I think dave didn't post more specific instructions because he hasn't done controlled testing. I posted on the site with a related question and here's what he said:

"Howdy Kevin,

I never measured the concentration, but it is small. CaOH is only weakly soluble in water. The easiest way to get a constant dosage would be to make lime water (by saturating CaOH in water and letting the residue settle). Lime water is stable and easy to store, then you can add that to cooking water. Much easier is to add CaOH straigt to the pot. Start with a couple of grams per liter and see how it goes.

With number 2, I think you’d have to soak or pre-water blanch before the oil to get the CaOH to the veggies. Please try it and let me know what happens."

I'm going to give this a shot and will report back.

I blog about science and cooking: www.sciencefare.org

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I did a few hours of testing this morning (hooray for off days!) and found that it doesn't take much CaOH to make a saturated solution. I added about a 2 tbsp to maybe a pint of water, and there was plenty of sediment at the bottom, even after vigorous shaking. While the CaOH had a noticeable effect on blanched green peppers, I wouldn't call the result... "desirable". I'll be trying more experiments over the weekend.

@dcarch: I have been toying with the idea of simply adding green food coloring to blanching water. I know most food-enthusiasts would probably be against food coloring due to its artificial nature, but if we're going to be adding things like Calcium Hydroxide and Sodium Bicarbonate to our blanching water to preserve color, is food coloring that far of a stretch? Thoughts?

Kevin

I blog about science and cooking: www.sciencefare.org

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Stupid idea to keep your veggies green:

In supermarkets veggie department, and meat department, they use special fluorescent bulbs which have special spectrums to enhance the green color and the red color.

------------

BTW, Kevin Liu has a very good point.

dcarch

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