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Why is my pesto turning brown?

roxlet Sep 30, 2011 04:59 AM

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.

  1. cowboyardee Sep 30, 2011 08:22 AM

    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).

    17 Replies
    1. re: cowboyardee
      HillJ Sep 30, 2011 08:41 AM

      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
        cowboyardee Sep 30, 2011 08:49 AM

        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
          roxlet Sep 30, 2011 09:02 AM

          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
            cowboyardee Sep 30, 2011 09:11 AM

            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
              roxlet Sep 30, 2011 11:53 AM

              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
                SourberryLily Sep 30, 2011 12:00 PM

                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
                  cowboyardee Sep 30, 2011 12:06 PM

                  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
                    roxlet Sep 30, 2011 12:28 PM

                    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
                      sr44 Sep 30, 2011 01:09 PM

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

                      1. re: sr44
                        cowboyardee Sep 30, 2011 01:32 PM

                        "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
              roxlet Sep 30, 2011 08:59 AM

              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
                cowboyardee Sep 30, 2011 09:01 AM

                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
                  acgold7 Sep 30, 2011 12:34 PM

                  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
                    cowboyardee Sep 30, 2011 12:47 PM

                    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
                      acgold7 Sep 30, 2011 12:50 PM

                      Except for the actual Basil itself.

                      1. re: acgold7
                        cowboyardee Sep 30, 2011 12:53 PM

                        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
                  rjka Sep 30, 2011 12:55 PM

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

              2. HillJ Sep 30, 2011 07:49 AM

                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
                  roxlet Sep 30, 2011 07:53 AM

                  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
                    HillJ Sep 30, 2011 07:54 AM

                    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
                      gourmanda Sep 30, 2011 08:28 AM

                      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
                        cowboyardee Sep 30, 2011 08:32 AM

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

                        1. re: cowboyardee
                          HillJ Sep 30, 2011 08:33 AM

                          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
                            cowboyardee Sep 30, 2011 08:42 AM

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

                  2. SourberryLily Sep 30, 2011 07:09 AM

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

                    1 Reply
                    1. re: SourberryLily
                      roxlet Sep 30, 2011 07:52 AM

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

                    2. m
                      magiesmom Sep 30, 2011 07:09 AM

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

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