Blanching Basil Makes Greener Pesto, But is it Worth It?

July 14, 2016

Just as your green beans will get greener when you blanch them in a pot of boiling water, so will basil. Following that logic, for greener basil send the leaves into boiling water (then shock them in an ice bath to stymie the cooking process).

It's a proven technique—that much we can agree on.

But what the pesto people cannot reach a consensus on is how much the blanching affects the overall product: Does it give a less flavorful sauce? The answers are mixed. While most agreed that blanching the basil dulls its flavor to some degree, the extent is contested.

Here's how it shakes out:

The blanchers

  • Fine Cooking calls basil-blanching "The Trick to Smooth, Creamy Pesto." Blanching is not solely for cosmetic purposes, but also for textural reasons: Cooked basil will emulsify more easily, resulting in a smoother sauce. "Blanching will slightly reduce the potency of the fresh basil flavor, but because a good bunch of basil starts out so incredibly fragrant, the reduction is minimal."
  • "Doing this leaches out a wee bit of the basil’s vivid flavor, but not enough to change that of the pesto significantly," writes Martha Rose Shulman in her recipe for Bright Green Pesto on the The New York Times.
  • Saveur includes blanching and shocking as part of a "classic version" of Genovese pesto to "give the sauce a brilliant green hue and to reduce any bitterness." (But the recipe for Emiko Davies's Pesto alla Genovese here on Food52 starts with raw leaves.)
  • Red Fern Farm laments discoloration as "the eternal problem of pesto-makers everywhere":

I was amazed at how much flavor the blanched basil retained, and how green my pesto was even after days in the fridge! I was a convert. I also found that, just like with fruits and vegetables, blanching my basil before freezing it made a world of difference.

  • The blog "Food and Style" lauds blanching as a method for "all of the flavor, none of the funky brown color" and is adamant on the flavor retention: "You may think that blanching the basil will take away some of its spunk, but be assured that it doesn’t. Indeed, the technique won’t take an ounce of flavor out of the aromatic leaves."
  • And different sources recommend different blanching times: Shulman warns against going over 10 seconds, while Michael Chiarello on the Food Network instructs 15.
  • And so does Tom Colicchio. Yes, even Tom Colicchio blanches! (Cue gasps.) "But if you make pesto my way—blanching the basil quickly and shocking it in ice water—you'll find that it stays bright green and that it tastes every bit as fresh as when it's made with raw basil. It even keeps the same, big, fresh aroma."
The difference is obvious!

The skeptics

  • The Kitchn tested the tip and declared it "mind-blowing... but with a caveat": "The winner here? Unblanched pesto by a mile. It tasted herbaceous, fresher, and well, like fresh basil. The blanched pesto's flavors were muted, and to be honest, didn't really taste like basil anymore." But, they conducted their taste with a 15-second blanch, much longer than Martha Rose Shulman (and others) suggests.
  • Daniel Gritzer, writing about pesto pasta for Serious Eats, is firm about the most important rule of cooking with pesto: "Don't cook it." We must assume that this applies to the leaves themselves, too.

In a departure from almost every other pasta sauce out there, all the charm of pesto is dependent on its fresh, raw flavor. Heat, and in particular prolonged exposure to high heat, is just about the worst thing for it. That's why most store-bought pesto is so disappointing: The high-heat sterilization necessary for canning and bottling cooks the basil, turning its volatile anise-mint scent dull.

  • But in another article, this one called "The Best Pesto," he concludes that "Because pesto is such a strong sauce, anything you do to reduce its pungency just a little and steer it towards a sweeter, rounder-flavored sauce, will help." That leaves the question, not addressed in that post, up in the air: Does blanching tone down the sauce, or make it less herby and more garlic- and cheese-forward and therefore sharper and more biting?
No one argues that blanching does *not* make the pesto brighter and greener.

So which is it? Does blanching really make a negligible difference?

Shop the Story

I doubled Martha Rose Shulman's Bright Green Pesto, blanching (just for 5 seconds, not 15) and shocking the basil in one batch, using raw leaves for the other.

Join The Conversation

Top Comment:
“That way you get a combination of the strong flavor of raw basil with some of the color retention/longevity characteristics from the blanched leaves. In a way, it's like cooking a dish with fresh herbs, then adding some more fresh stuff right at the end as a garnish.”
— 702551

The difference in color was remarkable and most of us thought the taste was, too. The pesto made with raw leaves was herbier, with an immediate and earthy basil flavor; the basil in the blanched pesto was more mellow, leaving more opportunity for the garlic, cheese, and salt to come to the forefront: It was flavorful, but not particularly from the basil.

Blanched pesto smeared on the left; raw pesto on the right.

Ultimately, most of us preferred the raw. (Sorry, Tom Colicchio.) But our photographer Bobbi could barely taste the difference, and said she would definitely blanch for the greener color alone.

My personal conclusion: I'd skip the blanching if planning to serve (or consume) the pesto that same day. But if I'm going to store it in the refrigerator (or the freezer) for some time, where it will continue to oxidize, the flavor degrading anyway, that's when I'd consider blanching first.

Does oxidized pesto bother you—and why? Tell us in the comments!

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See what other Food52 readers are saying.

  • SpinachInquisition
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SpinachInquisition July 27, 2016
I add a small handful of fresh spinach to boost the green color. It's undetectable in the flavor profile.
Babette's S. July 20, 2016
I'd never blanch basil (or other green herbs). At most, NuMystic & CV, my first thought after reading this article was to blanch part of the basil and blend it with fresh unblanched. You get the best of both the dark green world and the best of the super fresh natural basil aroma and taste. If using pesto with hot pasta or other cooked/hot food, I imagine the heat is going to affect the pesto to a certain degree (in color, aroma & flavor). Seems like an extra step for almost nothing in return. I'm perfectly content not blanching basil.
702551 August 3, 2016
I've done both. I've also added some fresh parsley (usually Italian flat leaf) to the pesto to perk up the color.

In any case, it's all personal preference.

My point here is that there are options to retain bright color over multiple days that hadn't been covered by the author.
NuMystic July 20, 2016
Compromising seems like an obvious best-of-both-worlds solution. Blanch half, leave half raw. The result will be brighter than raw, more herbaceous than fully blanched.
SonjaM July 16, 2016
I add a bit of plain yogurt - maybe a scant 2t per cup of pesto. I can't remember where I read this tip, but it works like a charm to keep pesto green.
David July 15, 2016
I add some vitamin C to the un-blanched mixture and the vivid green color is retained. Simple chemistry.
Mariko July 20, 2017
I add a pinch of citric acid powder while blending with the garlic and olive oil.
Alex C. July 14, 2016
blanched basil is cleaner. and roasted garlic for better flavor. Not just about green here.
mmeulendyk July 14, 2016
Just pack it down hard, so there are no air bubble and put a skim of olive oil over the top, it'll stay green for a while in the fridge.
Laura415 July 23, 2016
I also put oil on top of my pesto to stop oxidation. If I scoop any out I even it out in the container and try to cover it each time with a bit more oil. I might try blanching if I wanted to make a particularly smooth and less pungent pesto. These days I usually make a 4 herb pesto depending on what's available in the garden. It's rarely all basil even in the summer time. Oil works great. My pesto is much brighter than either of the pics and the oil keeps it that way.
Richard R. July 14, 2016
I have not tried this but I think I'll avoid it. Basil is easily rendered "grassy" by heat. Even adiabatic heat can do it. You can use some of the modernist stuff to keep the basil bright green and preserve the flavor of fresh leaves.
702551 July 14, 2016
One option not mentioned here is to blanch half of the basil. That way you get a combination of the strong flavor of raw basil with some of the color retention/longevity characteristics from the blanched leaves.

In a way, it's like cooking a dish with fresh herbs, then adding some more fresh stuff right at the end as a garnish.
702551 July 14, 2016
In the end, it's just personal preference anyhow.
Ruchi July 14, 2016
I really like this idea! I think it would be the perfect compromise
PHIL July 14, 2016
Good Morning Sarah, firstly lets add Blanch and Pesto to the vast list of cat names. Moving on, I do not blanch my pesto, because I am lazy and like your article about being the best cook you can be, it's not worth the extra effort. Also, I use it immediately and freeze the rest. Yes it can get dark but I am okay with that and usually I am adding it to something else anyway. Pesto screams it's presence on the first bite you taste, no need for the fluorescent green glow.