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OK, what happened to my pesto?

A couple of days ago, I found some picture-perfect Genoese basil at my local farmstand. I took it home, threw it into the food processor with the other requisite pesto ingredients (pine nuts, good olive oil, Parmesan, salt, pepper, garlic) and made a lovely looking and aromatic pesto. I decanted the stuff into a glass bowl, coated the top with more olive oil and put it in the refrigerator, well wrapped, where it stayed, sealed, for 24 hours.

When I sauced some pasta with this pesto the next day, it oxidized on contact, turning a dull olive brown color. Worse, it lost a great deal of its flavor.

Can any of you help diagnose the problem? Was my mistake storing the stuff? Does homemade pesto need to be used immediately? And if so, how does all-natural, commercially packaged pesto retain its color and flavor sitting in refrigeration for considerably longer than a day?

Any and all advice would be welcome!

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  1. It needs to be used immediately, or frozen, in my experience. I freeze it in ziplock bags, flattened out really thin, so I can just break off a chunk. It keeps its color way better this way. Some people leave out the nuts when they freeze it, but I don't know why. You didn't do anything weird, basil leaves oxidize super fast.

    1 Reply
    1. re: Betty

      Leave out the nuts when you make it to freze; freeze it right away.

    2. I think commercial pesto has some kind of preservative in it, perhaps citric acid?

      I make pesto in bulk whenever I see good basil in the local markets. I find it turns brownish on the surface, but beneath that thin layer it's still a bright green. The flavor fades with time, but it holds up for a couple of months in the freezer. I should add that I look for Thai basil for my frozen basil, it has more intense flavor and this may make a difference.

      1. Thank you both--this is enormously helpful. I will trying freezing in Ziplocs, and using Thai basil.

        2 Replies
        1. re: lisacs

          Hi, you mite also try adding just a little bit of lemon juice to the pesto your going to hold for a day or so or freeze. I think it will help with the color and won't change the flavor if you use very little. Good luck--there is nothing like great pesto!

          1. re: jackie de

            I also use some lemon juice to reduce oxidization.

        2. Basil oxidizes easily when cut with a knife blade and exposed to air. For uses where it doesn't have to be pulverized it's better to tear it. Yet, I have some Costco Kirkland all natural pesto in my fridge for months that still looks and tastes fine. Label says it contains rice vinegar as the only thing I think would retard oxidation. If I wanted to make some at home I would do it immediately before eating, or maybe an hour before. You might be able to store it if you vacuum packed it in a plastic bag with one of those handi dandi electri vacuum sealers (Deni is a popular brand available reliably at QVC.COM)

          1. If I know I need to keep my pesto longer than it can safely sit out on the counter, I (VERY briefly) blanch the basil in boiling water -- 5 seconds tops -- then shock in ice water to stop the cooking. Pat dry, and it sets the colour.

            1. To preserve the color of pesto I blanch the basil for just a few seconds in boiling water, fish them out and shock them in ice water, then drain and squeeze. Yes, you lose the raw texture. Normally I don't bother to blanch, but the blanched basil pesto stays bright green on a potluck pasta salad, or for many days in the fridge.

              Another thing that helps, although not for as long as blanching, is to add a little vitamin C powder (an antioxidant, you can just crush an unsweetened tablet) - it acts like the citric acid in commercial stuff.

              1 Reply
              1. re: Junie D

                Junie D has it right -- blanching the basil extracts just enough of the extra water in the leaves that oxidation happens much, much more slowly. And the addition of a little ascorbic acid just about stops it completely, although I rarely bother -- I think this is why commercial pesto tastes, well, commercial. I don't find blanching compromises flavor -- in fact, this is how I prep fresh basil for freezing after my summer monsoon harvests. Blanch, press out the extra water, and vacuum seal -- that will keep you in bright green basil until next summer, if you don't want to resort to the overpriced, wilty supermarket stuff.

              2. Blanching does set the color but for myself I don't like the blanced basil pesto very much, so it's worth it to me to make and eat the pesto on the same day (with other pestos, such as spinach, arugula, walnut, sundried tomato, etc., the oxidation is not as bad or is non existent, so I will make those the day before (and will use a little lemon juice with the arugula pesto)). But everyone's taste buds are different so for the sake of science (!) you could do a small batch of each, head to head, and see if you like the taste or not. At the end of basil season I make a bunch of pesto and freeze it in separate bags, enough to dress one pound of pasta. The only thing I leave out when I freeze it is the cheese and butter (sounds strange but it really makes the pesto creamier and smoother if I add a tablespoon of softened unsalted butter just before serving). I add those after I've defrosted the pesto, just before tossing it with the pasta.

                1. I once saw Michael Chiraello on the Food Network make pesto and he added Vitamic C powder (aka citric acid) to the pesto to keep it green.

                  2 Replies
                  1. re: bostonfoodie111

                    Vitamin C is actually ascorbic acid - but is an antioxidant like citric acid

                    1. re: Junie D

                      oops - I knew that... :) "Surprise", I'm not a chemist! ;)thanks for the correction...

                  2. I have 15 Basil Genovese plants and make *lots* of pesto every summer. I freeze most of it, and I find there is no flavor loss even after one year. Also, I have kept pesto in the refrigerator more than 24 hours, with no flavor loss.

                    After years of making pesto, I have found one secret. Have extra of each component, not just what the recipe calls for. This way you can add more pine nuts if it tastes "too green", more Parmesan for increased depth and saltiness, etc.

                    It does turn an olive green, which does not bother me. Perhaps the color change influenced your "buds", as we "eat with our eyes" first.

                    7 Replies
                    1. re: Funwithfood

                      I agree, the color change doesn't bother me. I don't notice it these days. I have always frozen pesto without the cheese, preferring to add it when I make the pasta. Now I'm trying it without the garlic because I think the flavor is better when it's fresh.

                      1. re: cheryl_h

                        Please report back on how that works for you.

                        I add the cheese and garlic before freezing, and find it to taste the same as freshly made. Maybe there is a difference, but it is so minute as to be imperceptible to me (or my family).

                        The convenience of being able to have pesto 'at the ready' is so wonderful--especially with the huge quantities I make!

                        1. re: Funwithfood

                          Thanks, everyone--you have inspired me to hit the farmer's market this weekend and experiment: maybe one batch with Thai Basil and more assertive seasoning, one blanched, and one with some sort of citric acid goosing. Will report back on the Great Pesto Cookoff next week!

                          1. re: lisacs

                            Of course, to be scientific (g), you need to have a 'control group'--that is one batch prepared exactly as you did your first. : )

                            1. re: lisacs

                              True, but the SO complained so much about the lack of flavor in that last batch that I think we'll just rely on the (insipid) memory of it...

                              Pesto is truly one of those items about which people hold strong opinions. Speaking of which, does anyone have a good recipe for arugula pesto they'd care to share? That sounds good, and next month the arugula will be coming in at our market in a big way.

                              1. re: lisacs

                                I use this version of arugula pesto, from Michael Chiarello, but I don't add the vitamin c and I add some lemon juice to taste. http://www.foodnetwork.com/food/recip...

                                1. re: lisacs

                                  As far as the assertive seasoning goes, try adding a small quantity of fresh oregano to your basil...Somthing Greek or Sicilian, if you can find it. The contrast with the earthy oregano really makes the basil flavor *pop*...

                          2. Does anyone use a mortar and pestle to make pesto and if so how does it compare to pesto made in a food processor?

                            1 Reply
                            1. re: free sample addict aka Tracy L

                              I often make pesto in a mortar (esp. for small quantities, because I hate cleaning my food processor) -- it has more "body" than food processor pesto, but it doesn't absorb as much oil -- which can be a good thing if you're counting the calories, and a bad thing if you overdo the oil, because you'll end up with an oil slick.

                            2. Thanks, farmersdaughter!

                              I have made other herb-based sauces in a mortar and pestle. It takes a lot of patience, but if the oxidization of the basil is caused by contact with metal blades, as someone suggested earlier in the thread, then mortar and pestle pesto would probably stay green longer.

                              2 Replies
                              1. re: lisacs

                                In one of the posts above you describe the pesto as "insipid". Could the problem be as simple as not enough basil? I've never know pesto to be insipid unless something is wrong with the basil, and it sounds like your Genovese basil had plenty of flavor. If you still have the pesto, try add more crushed basil to it and see if that's all it needs.

                                1. re: lisacs

                                  The oxidization of basil is from contact with air. The word oxidize means to come in contact with oxygen. The metal blade of the knife has nothing to do with it. Use a very sharp knife and slice rather than chump down on the basil and your cut basil will not have any brown edges. Tearing basil also works because less bruising of the basil, less basil coming in contact with the air.

                                2. I've read suggestions to add some parsley to your pesto because parsley stays green. Haven't tried it myself. I now associate that dark green color with good flavored pesto and am suspicious of anything bright green -- it looks wrong!

                                  3 Replies
                                  1. re: Karen_Schaffer

                                    I tried adding parsley one time--did not like it at all.

                                    1. re: Funwithfood

                                      I think curly parsley is too tough. Italian parsley might not be bad.

                                      My last few batches of pesto stayed bright green. I have no idea why.

                                      1. re: Ruth Lafler

                                        I used Italian parsley--did not like it (dilutes/distorts the intensity of my pesto.)

                                  2. I find the taste of ascorbic acid and lemon juice kind of unpleasant in pesto, to be honest. If I need to keep pesto for any length of time, I use a dash of white balsamic vinegar-- especially when the pesto is going to be added to something with balsamic in it.


                                    NYCnosh: http://nycnosh.com

                                    1. I second Funwithfood--I don't think parsley is a useful addition to pesto, and when I tried it in the past, it had no discernable effect on the color of the pesto. On the other hand, parsley and walnut pesto, made with Italian parsley and very fresh walnuts, is a decent fall/winter sauce.

                                      I'll probably try Nosher's suggestion about vinegar rather than citric/ascorbic acid--our favorite farmer's market pesto has rice vinegar as a stabilizing ingredient.

                                      On reflection, taking into consideration what everyone has said, I think there were probably two factors draining the flavor and spark out of my pesto: (1) the basil I used, while nice to look at and tasty enough in its fresh state, was just too mild-mannered to hold its own in a sauce. I've made pesto in previous years using the same proportion of basil by weight to pine nuts/oil/cheese and have had far more flavorful results, so I don't think the recipe itself is the problem. And then (2) when I refrigerated, I probably should have put the stuff into a Ziploc and squeezed out as much air as possible. Or topped my pesto with a more liberal coating of olive oil.

                                      1. I read in a recent edition of Cook's Illustrated that adding baby spinach helps keep the pesto green and it really does work. It also adds a velvety texture to the pesto.

                                        1. Thanks for the tips on storing pesto. I'll try freezing. Also, I use the juice of 1 small or 1/2 large lemon for 8 oz. of basil/arugula. Try adding 2 T. capers to the mix. I use roasted walnuts instead of pine nuts, but that's just my preference. I made a batch with 3 oz arugula and 5 oz. basil, both from my garden. Nice to have something to do with that arugula late in the season when it gets too strong for my salads. Put over some whole wheat vermicelli with some sliced fresh ripe tomato and some extra parm, and wow, it was delicious.

                                          1. Would you mind posting your pesto recipe?

                                            1. sorry for the arrogance, however, the replies are mostly mistaken. There was obviously a problem with one of your ingredients here. Regardless of the type of basil, ect....the pesto should not have done this. Pesto should discolour slightly when left in contact with the air, but not on contact with your pasta. Perhaps you microwaved the pasta and the intense heat played a role? I dont know. Basically, try again and see what happens. It should keep for at least a week, no matter if its only in a bowl in the fridge, with a bit of darkening on the top.

                                              1. p.s. was the basil dried after washing, water will ruin it.

                                                1 Reply
                                                1. re: pesto expert

                                                  Hi, pesto expert:

                                                  Thanks for the tips. The basil was dried before I used it but probably not 100%, so water is one possible culprit. I did not microwave the pasta--this was freshly cooked and the pesto just blended in at the moment it was to be served.

                                                  Since my original post, I made one more batch of pesto with a teeny bit of lemon juice. No massive discoloration as before, but this time the leaves I used, which were large and rather tough, didn't have great flavor. Perhaps pesto and I were not meant to be...

                                                  I think the best-tasting pesto I've ever made was with smaller leaves from Genovese basil plants. Will try again next summer before the plants get too big. For now, I'm concentrating on end-of-summer tomatoes: tomato-basil sauce and slow-roasted tomatoes in oil. We've had a great crop this year, and I have a good supplier for heirloom varieties that make excellent sauce.

                                                2. Here is your answer:

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

                                                  So, you were right "lisacs", contrary to what "pestoexpert" says, your change in bright green did happen upon contact with the heat in the pasta.

                                                  Shirley Corriher, author of "Cookwise", elaborates on this"

                                                  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."
                                                  (excerpt from http://splendidtable.publicradio.org/...


                                                  In essence, we have two culprits and not only one, the acid and the heat working together.

                                                  1. I press plastic wrap directly to the pesto I intend to store keeping out a bit of air, and it seems to prevent color change when refrid'd.

                                                    1. Thanks to everyone for continuing to suggest ideas and remedies.

                                                      I think Floyd may have hit it on the head with the food science research. We recently started cooking with Barilla Plus pasta--it is whole grain with flaxseed and other virtuous things added to it, which may have triggered the reaction Shirley Corriher describes. As I mentioned, the stuff turned muddy brown on contact with the pasta, not before, so I think my storage methods, chopping techniques, and ingredients were not so much to blame.

                                                      Will try the lemon juice trick.