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Old 10-10-2006, 12:38 PM   #1
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Acid on Greens

I have come upon something that has me stumped...

In vegetable cookery at culinary school, it was a given that acids dull the green color (chlorophyll) in vegetables therefore it must be added towards the end (ie, green beans tossed in tomato sauce right before plating). With red vegetables, acid improved the color and with whites it helps set the white color.

Now I have come upon several observations, in particular a recipe by Michael Chiarello for pesto, which specifically call for Vitamin C/citric acid/ascorbic acid to set the green color in the pesto. He blanches the basil leaves 15 seconds and then shocks in ice water, then dries it, then purees it w olive oil, the usual pesto ingredients and the acid. As stated, the acid is there to keep the pesto looking green for a longer time.

Ok, so what gives? The chlorophyll in the vegetables is the same as the chlorophyll in the herb (basil), so what changes? Am I overlooking something - am i missing something here? Ironchef, Michael in Ftw, Andy M, Nicholas.... anyone?!

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Old 10-10-2006, 12:42 PM   #2
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I see two options:

1. The blanching sets the color so the acid doesn't matter

2. Michael Chiarello isn't the most accurate shen it comes to explaining the whys behind cooking. I've caught him making several errors on his TV show.
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Old 10-10-2006, 12:53 PM   #3
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Quote:
Originally Posted by Andy M.
I see two options:

1. The blanching sets the color so the acid doesn't matter

2. Michael Chiarello isn't the most accurate shen it comes to explaining the whys behind cooking. I've caught him making several errors on his TV show.
Point 1 - interesting theory

Point 2 - thats a given, however, Shirley Corriher uses this technique:

Keeping Pesto Green
"When adding pesto to pasta it can turn from bright green to a drab, mucky color. The basil is reacting with a compound in the pasta. There's a simple way to remedy this, add a little lemon juice to the pasta water before adding the pasta or add lemon juice to the pesto. This will stop the chemical reaction and keep the pesto looking brighter and fresher."

Even though the application here is slightly different, the acid is still "helping" to set the green color...

Howard Hillman in "Kitchen Science" states something interesting: "acid, coupled with heat, is the villain - in combination they denature chlorophyll"

Have I found my answer then?
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Old 10-10-2006, 01:06 PM   #4
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That tells me that you don't have to set the color in the pesto. What the addition of the acid does is prevent the compound in the pasta from reacting with the pesto to dull the color.
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Old 10-10-2006, 01:15 PM   #5
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hmm... exactly!! so, according to our observations so far (im thinking out loud here), the optimal would be:

1 - blanch and shock basil to set the color, then dry thouroughly
2 - process with olive oil, pine nuts, salt/pepper, parmigiano (if being used right away)
3 - cook pasta, and toss with pesto and a spritz of lemon juice

i believe I am no longer stumped!

anyone else care to get me back in stump mode? Have we missed something once again?
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Old 10-10-2006, 01:19 PM   #6
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I think the blanching sets the color. I have made chive oil and mint oil that are BRILLIANT green because of blanching. Beautiful stuff.
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Old 10-10-2006, 01:22 PM   #7
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The addition of Vitamin C or Ascorbic acid helps to prevent discoloration in foods. Citric acid is different from Ascorbic acid and should not be confused with each other. I use Vitamic C powder to help retain the color of infused oils and other types of sauces (i.e. a watercress coulis) that would otherwise lose it's color through oxidation if not made and used right away. Not only does ascorbic acid help with the retention of color in greens, it also helps to prevent browning in other things such as fruits. That's why things like frozen peaches or bananas that you buy pre-packaged have ascorbic acid added to them.
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Old 10-10-2006, 01:54 PM   #8
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Quote:
Originally Posted by ironchef
The addition of Vitamin C or Ascorbic acid helps to prevent discoloration in foods. Citric acid is different from Ascorbic acid and should not be confused with each other. I use Vitamic C powder to help retain the color of infused oils and other types of sauces (i.e. a watercress coulis) that would otherwise lose it's color through oxidation if not made and used right away. Not only does ascorbic acid help with the retention of color in greens, it also helps to prevent browning in other things such as fruits. That's why things like frozen peaches or bananas that you buy pre-packaged have ascorbic acid added to them.
Good point, Vitamin C = ascorbic acid <> citric acid

question: so the lemon juice has both ascorbic acid AND citric acid? it would seem so in order to work in Sally Corriher's example
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Old 10-14-2006, 04:46 AM   #9
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Seven - see if you can get your hands on a copy of Harold McGee's The Curious Cook ... he has several (5-6 if I remember right) pages devoted to the problem of pesto going "camo funky" ....

Without digging it out and trying to copy several pages here ... basically, vegetables go funky camo green from the chlorophyll which you can "set" using the Julia Childs "7-Minute" rule .... never boil them for more than 7-minutes and then "shock" them so they don't continue to cook.

The problem with the "pesto" has to do with browning enzymes being exposed to air which have nothing to do with being heated like green vegetables (similar to avacados but different) ... but the browning enzymes can be "killed" in short order by blanching for as short of a time as 15-sec and then shocking in ice water.

I'll go dig out Shriley Corriher's Cookwise and McGee's Curious Cook if you have any more questions.

Basically - your "de-stumping" method should work!
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Old 10-14-2006, 03:50 PM   #10
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I agree with Gretchen - the blanching sets the color.
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