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Sep 30, 2011 04:59 AM

Why is my pesto turning brown?

I have been making pesto nearly my whole life, and suddenly, I am having a problem with my pesto turning brown. Of course, pesto will oxidize when exposed to air, so I always put a layer of olive oil on top of my pesto when I store it. But this browning is nearly instantaneous. Parts of it are browning when I remove it from the blender jar. I've never, ever had oxidation happen like this. And when I am serving it, it is brown instead of the bright green that I am used to. It tastes the same, but I find the color less appetizing. This is from basil grown in my garden, so I am wondering if it is possible that certain cultivars oxidize more readily? Is this possible? Maybe it is just not a good basil for pesto? Weird.

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  1. I have had that experience with some cultivars also. not sure why.

    1. Hmm weird. Although, maybe it's the olive oil? What kind are you using?

      3 Replies
      1. re: SourberryLily

        Same as always. Same everything! Our general use olive oil is Bertoli extra virgin.

        1. re: roxlet

          i realize this is an older post but bertolli hasn't been "genuine" olive oil for a long time.

      2. I read on cooksillustrated some time back that if you blanche the basil before you make the pesto, it keeps the green color. Lemon too. Adding parsley is another trick. And because the frig does a sluggish thing to olive oil, I don't top it. I freeze pesto in small batches and add olive oil as I use it.

        6 Replies
        1. re: HillJ

          Yes, I have read that as well, but in the past, I never had a problem with the pesto turning brown even though neither blanched it nor added lemon...

          1. re: roxlet

            Could just be an odd crop of basil; somethings creating the oxidation in the leaves. As long as it smells right, tastes right I wouldn't be overly concerned about the quality..but, I agree the color is off putting.

            I would recommend blancing your next garden bunch and see if it makes a difference.

            1. re: roxlet

              Please don't blanch! I tried it and yes, I have nice and bright green pesto. That has no flavor :( Very disappointed.

              1. re: gourmanda

                I'd hesitate to blanch for the same reason. Trading flavor for color is usually not something I'm interested in.

                1. re: cowboyardee

                  Blanche two seconds, dip in ice water 2 seconds. Drain on paper towels and proceed as normal. Works great for me.

                  Or, add lemon to your made pesto.

                  Or, add a few leaves of parsley.

                  No loss of flavor. :)

                  1. re: HillJ

                    Admittedly, I haven't tried it. Just my suspicion.

          2. One more potential factor: could also be that your blender blades are getting very dull. Generally speaking, the more tearing and less cutting you do to the basil, the quicker it will oxidize. This dulling can even happen very suddenly if you happen to blend something very gritty or hard - your blades can go from quite sharp to quite dull in no time.

            It's also possible that the basil itself is a factor, but I don't know a whole lot about whether or why some basils oxidize quicker than others.

            As others have said, adding lemon juice (which acts as an antioxidant - lime juice also works) can help. Depending on how much olive oil you put on, you might benefit from either a thicker layer (if you only drizzle), or from covering the top of the pesto with plastic wrap (directly on the pesto, not just over the top of the container).

            19 Replies
            1. re: cowboyardee

              I'd love to know if what you're saying about blades makes a difference.

              (I know a dull blade will ruin my lawn.... or, frustrate me in the kitchen...but ruin pesto..hmmm)

              1. re: cowboyardee

                Another thing that might help - if you're starting the blender off with only the dry ingredients and then slowly drizzling oil in, try adding a little oil before starting the blender. It should help protect the cut basil from excess air exposure. You're not going for a mayo-like emulsion really, so a slow drizzle isn't really necessary.

                1. re: cowboyardee

                  No, the way I make it is that I put it in the food processor first, and then put it into the blender to get kind of creamy and emulsified, which is how I like my pesto to be. I don't like to see the little basil bits. But I've been doing it this way for YEARS and never had this problem before. I think what I am going to do is to buy some basil at the farmer's market tomorrow and make another batch and see what happens.

                  1. re: roxlet

                    I'm not saying you've changed the recipe. I'm just saying that including some oil early on in the process adds a little extra protection.

                    Also, if you start off in the food processor, dullness in those blades is another possible reason for the recent increase in oxidation rate.

                    1. re: cowboyardee

                      Thanks for the idea, but it is highly unlikely that the blades of my FP are dull since it is a new one. I grate the cheese first with the pignoli and garlic, and then add basil and olive oil together, so I am already doing what you suggest. After it is somewhat amalgamated, I put it in the Vita-Mix with additional olive oil if necessary.

                      1. re: roxlet

                        From an article in allrecipes: "Fresh basil is very delicate, and will turn brown if it gets very hot or if it's exposed to air for long periods of time. Many cooks use fresh spinach as well as basil in their pesto to help maintain its brilliant green color."

                        Could it be the temperature of your ingredients? Maybe it gets hot in the blender?

                        If you're guaranteeing that the ingredients and brands used are exactly the same, then it might have something to do with the way you're doing it, or the environment.

                        Or it might be that one of your ingredients (obviously not the basil) is older and has changed on a chemical level. I'm not a expert on pesto, i mostly do chocolateering, but age and method is a big difference in baking. Maybe it does with this as well...

                        PS: Maybe you could try the spinach trick, to cheat?

                        1. re: roxlet

                          If you haven't changed a single thing about the way you make it, the only explanations that sound especially plausible to me are dull blades in one device or the other, or else something different about the basil you're using.

                          It could be the basil. It is late in the season and it's plausible that the basil you're growing right now is more damaged or lower in natural antioxidants than what you've used before. But that's about as much as I can say intelligently about the matter. If you try it with another basil, please let us know how it turns out.

                          1. re: cowboyardee

                            The more I think about it, the more I think that it has to be the basil. I made pesto with it earlier in the season, and it, too, turned brown, so it is not a result of being "late season." Prior to that, I had purchased basil, and the pesto stayed green. I am definitely going to try this with other basil, and I will report my results.

                            1. re: cowboyardee

                              But the food processor is new. The contents of the bowl can get pretty hot during processing.

                              1. re: sr44

                                "The contents of the bowl can get pretty hot during processing."
                                But then why would that be any different from how the OP's made it before?

                                I'm thinking the OP is probably right - the basil is the most likely explanation. But if a change of basil doesn't help, then take another look at those blades. Even new blades can go dull very quickly if you grind something harder than the steel (something with some sand on it, or a hunk of something that shouldn't have been in there).

                    2. re: cowboyardee

                      No, the blender blades are very sharp. It's a Vita-Mix and I could make gravel in it. Most definitely not the blades. Plus, when it's done, it's a bright and beautiful green, and then starts oxidizing almost immediately.

                      1. re: roxlet

                        A vitamix is a fine blender. But its blades are still only metal. Thing has so much power and blade speed that it'll still blend long after the blades are dull. In other words, just because it works doesn't mean the blades are sharp.

                        I have some wonderful knives, but they still get dull. Just sayin...

                        1. re: cowboyardee

                          I think the blades are a non-issue. Pesto gets its name from the fact that it was originally made in a mortar and pestle, so the basil was smashed rather than cut. So if the ideal authentic pesto is supposed to be green, sharp blades aren't even part of the process and in fact, duller blades should theoretically be better.

                          At the same time, I do realize that over-cutting certain herbs can make them turn black, so I dunno.....

                          1. re: acgold7

                            I doubt it's the only issue, and ir my not be one at all in this case. However it's one of the few plausible factors i can come up with given that the OP has truly changed nothing in her recipe.

                            1. re: cowboyardee

                              Except for the actual Basil itself.

                              1. re: acgold7

                                Already an admitted possibility. See above. But unless the OP tries it with another type of basil, there's not much I can add.

                        2. re: roxlet

                          Could it be residue from something else on the blender/blender blades interacting with the basil?

                        3. re: cowboyardee

                          Dull blender blades were what I thought too.
                          Next time hand chop the basil with your sharpest knife. See if that makes any difference.

                          1. re: Puffin3

                            I have a Vita-Mix, and the blades are not dull. It's not the problem. I will try again soon, and will report back.

                        4. I am having the same problem. I have had to toss all of my basil this year because it got Downy Mildew so I bought sweet basil from the farmers market (organic) and it did the same as you. It was an ugly brown before I even finished the batch. I will read comments below. Just read replies and will try lemon/parsley. I'm so sad about the Downy Mildew problem in our area (northern Illinois).

                          1 Reply
                          1. re: EJReb

                            Sorry to hear that you're having this problem. I haven't made pesto this season yet, so I'll have to see if the problem persists with this year's basil crop...