Acid on Greens

[Seven S]

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?!

 

[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.

 

[Seven S]

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?

 

[Andy M.]

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.

 

[Seven S]

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?

 

[Gretchen]

I think the blanching sets the color. I have made chive oil and mint oil that are BRILLIANT green because of blanching. Beautiful stuff.

 

[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.

 

[Seven S]

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

 

[Michael in FtW]

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!

 

[shpj4]

I agree with Gretchen - the blanching sets the color.

 

[Nicholas Mosher]

Hmmmm... as far as I know acids plus chlorophyll equals army green.

If you have McGee's "On Food and Cooking" (you do, don't you? ) refer to the "Cooking Fresh Fruits and Vegetables" section. Knowing a bit of chemistry is good here too (grab a text at Barnes & Noble).

There are two ways green vegetables lose their color or turn nasty. They either lose their chlorophyll to the surrounding water, or undergo a reaction where the chlrophyll is transformed into a molecule with different color attributes. An enzyme active between 150-170ºF called chlorophyllase can strip the chlorophyll of it's hydrocarbon tail and causes it to become water-soluble rather than fat soluble. It then leaks out into the cooking water. Chlorophyllase is destroyed at the boiling point, so keeping the water at 212º is important. Letting it drop to the 150-170ºF range by not having enough water to make up for the heat the vegetable is sucking out of the water exacerbates the problem. So use lots of water, or steam, which actually allows you to quickly raise the ambient temperature in the pot/pan above 212º with a heavy lid. Don't pile the veggies though, or they will insulate each other and you will get a slow temp increase where the covered veegetables will be in that 150-170ºF range a long time.

Chlorophyll molecules have a magnesium atom at their center, which can be displaced by heat and/or natural enzymes in the plant itself. This then allows hydrogen ions to move in and turn chlorophyll-a into pheophytin-a (grayish-green), and chlorophyll-b into pheophytin-b (yellowish). When an acid is added to water it separates and creates a butt-load of hydrogen ions. When it comes to keeping chlorophyll bright green, adding acid is like sticking a fork in your eye. You can actually help prevent this by adding alkaline substances like sodium-bicarbonate (baking soda) - but if you add too much it can make the veggie mushy. Most tap water is slightly alkaline to prevent pipe-corrosion, so this usually isn't a problem - but fruits & veggies alos have natural acids that can affect the chlorophyll in the same way.

The trick is to cook at high heat with lots of water (destroying chlorophyllase), and cook only long enough to collapse the air pockets in the cell wall/membrane (allowing the chlorophyll is be seen) and then quickly stopping the cooking process before the heat displaces too many of the magnesium atoms and too many acids are released to replace the displaced magnesium.

Now I only passed CHEM I in college, so someone here with more smarts/experience can probably do a much better job...

I'm not quite sure how adding another acid later helps to preserve the color. Sounds kinda like it would be counter-productive? I dunno.

 

[Nicholas Mosher]

Ha, I realized this was about pesto using basil which is susceptible to phenolic browning. It's ok, McGee has that too... let me brush-up...

 

[Nicholas Mosher]

Ok, phenolic browning is caused when phenolic compounds in the cell's vacuoles mix with enzymes in the cell's cytoplasm in the presence of oxygen (pick up a basic micro-bio book for this great info!). So it takes three components. You can either remove the oxygen by keeping the pesto covered in oil (and grinding it with oil), or you can deactivate the enzymes in the cytoplasm by blanching the leaves.

Good experiment. I've never tried blanching my basil leaves before making pesto.

Apparently Vitamin C has natural anti-oxidants that prevent the phenolic browning as well. I guess once you process the pesto, the fat soluble chlorophyll is protected by the olive oil from the vitamin C, and then vitamin C goes to work preventing the phenol reaction.

I think thats it.

 

[TATTRAT]

Acid in the greens, Steve? Bring some of those up next time! whoa...the colors!

j/k.



Seems like everyone has posted some great info, I learned something.