How they keep store-bought pesto green

[Fat Guy]

How do they keep store-bought pesto green? I have some from Costco. It doesn't seem to have any weird chemicals in it. Yet it has stayed green for like a month. What's the trick?

[slkinsey]

Acid. Either ascorbic or citric.

[Fat Guy]

These are the ingredients:

"Ingredients: fresh basil, extra-virgin olive oil, canola oil, non-GMO and rBGH-free parmesan cheese, pine nuts, fresh garlic, rice vinegar, salt and black pepper."

Might it be the vinegar playing the role of acid?

[slkinsey]

I'd think so, yea.

[gfweb]

It might just be blanched which makes a big difference in holding basil color. I experimented a few mos ago with excess basil. 45 sec in boiling water and it stayed green for hours (until I ate it). It tasted less basil-y than the unblanched brown stuff though. Probably blanching sous vide would protect the flavor.

[StanSherman]

Besides the acid, generally the harvest to process time is usually faster. My homemade stuff stays pretty green since it goes into the mix within 10 minutes of cutting.

[Lisa Shock]

They also probably pack it with a gas instead of plain air, too. This way, there's no oxygen to cause oxidation.

[ScoopKW]

+1 for blanching. After making the pesto, cover the top with some olive oil and freeze it solid. I've kept garden pesto green for months that way. I freeze it in small containers that are useful sizes for various applications.

[qrn]

+1 for blanching. After making the pesto, cover the top with some olive oil and freeze it solid. I've kept garden pesto green for months that way. I freeze it in small containers that are useful sizes for various applications.

I dont blanch but roughly chop it in the food processorwith a touch of OO and put it in ice cube trays and freeze,then vac pack the cubes, will keep for at least a year...(using Genovese Basil from the garden as well)

Bud.

[Kevin Liu]

By quickly blanching the basil, you deactivate chlorophyllase, the enzyme responsible for the breakdown of chlorophyll, so that definitely contributes to preserving color.

Unfortunately, I don't think acid should help preserve the green color. Rather, high acidity replaces the Magnesium in chlorophyll with H+ ions, resulting in the production of olive-drab and yellowish pheophytin compounds.

This is my best guess at what is happening: basil's color is preserved by a quick blanch. The resulting chlorophyll then leaches into the olive oil (chlorophyll is oil soluble), giving the oil itself a bright green color that cannot be affected by acidity. the rest of pesto will slowly turn brown in an acidic environment, but it won't be as easy to see because the oil is so brightly colored.

It'd be really interesting if you could measure the pH of the pesto to see if it's acidic or basic; maybe I'm totally off. I'd be interested to see what you get, I just put up a post on keeping stuff green on my blog and I feel like there must be a better way than simply adding pinch of baking soda to cooking water.

[Kevin Liu]

I did some more reading on this, and it looks like I was wrong.

It appears the main reason pesto turns brown is due to enzymatic browning, which is why blanching (which deactivates enzymes) and acids (lowering pH, plus antioxidant properties) can help keep pesto green.

[azlee]

McGee on keeping pesto green

[runwestierun]

I make alot of pistou, kind of a pesto without the cheese or nuts. It never turns brown. What in the cheese and/or nuts could be turning it brown?

[ChrisZ]

It'd be really interesting if you could measure the pH of the pesto to see if it's acidic or basic; maybe I'm totally off. I'd be interested to see what you get, I just put up a post on keeping stuff green on my blog and I feel like there must be a better way than simply adding pinch of baking soda to cooking water.

I read about this somewhere but can't find it now... the thing about store bought pestos is that they have to conform to a range of health & safety guidelines. Anything stored and sold in a jar needs a ph low enough to prevent botulism breeding - this is especially true for fresh fruit and vegetables, including herbs. I can't recall the exact ph, but it's low enough - ie. acidic enough - that store bought pesto will never taste the same as the stuff you make at home. The same goes for those tubes of pureed herbs/garlic/ginger that can be very convenient- they have to have a low enough ph that it noticeably affects the taste.

Because of botulism concerns, it's a safe bet that store-bought pesto is made from blanched basil, and this is the biggest factor in keeping it green. The low acidity, while effecting the taste, will actually help dull the colour - there's more on this in McGee's OFAC.

[ChrisZ]

This piece on producing perfect pesto popped up on the SMH today... it claims that adding salt helps preserve the green colour of the basil.

[Kevin Liu]

I think the salt thing has to do with water activity. I dug up a paper today titled "Use of humectants for the stabilization of pesto sauce." by Severini et al that seems to indicate the availability of water in pesto has a direct relationship with preserving green color. This is also probably why you're supposed to squeeze all the water out of blanched pesto.

and by the way the article mentions that commercial food processors will pack pesto in artificial atmospheres that are low in oxygen to further prevent oxidation.

[mgaretz]

I made some fresh pesto about a week ago. It was olive oil (about 2/3 cup), one bunch of basil, a small garlic clove and about 1/2 tsp salt. I put the salt in due to this thread, but no vinegar and no cheese. All into the BlendTec and then into the fridge. Tonight I used it on pasta:

It's still a nice bright green.

When you taste the pesto straight, it's a bit salty, but the saltiness disappears when on the pasta.

Edited to add that I didn't blanch the basil either.

Edited October 11, 2011 by mgaretz (log)