The darkening of the guacamole or avocado is due to the process of oxidation – reaction with oxygen in the air. The skin of the fruit, whether apples or avocados, provides protection from this process until it’s broken.
Before I go on, I will start off by saying that I was a chemistry major in college. So I find things like this quite fun. Yes fun. I am a major nerd. So if you want to skip over the next few paragraphs and right into the instructions, I will not be offended; it’s because you are probably much cooler than I am. And believe me, that wasn’t an attempt at self-deprecation or sarcasm. It’s highly likely a statement of fact. 😛
I will be very brief. But I believe that a basic understanding of the process comes in handy. And knowing WHY you are doing what you are doing will help you do it correctly.
The change in color occurs through a process called enzymatic browning. Polyphenol oxidase, which is present in avocados as well as other fruits/plants, is an enzyme that catalyzes this process. When Polyphenol oxidase is exposed to air, it combines with the oxygen and catalyzes the oxidation of phenolic substrates (phenols that the enzyme acts upon) endogenous in avocados into quinones, which undergoes further polymerization reactions to yield melanin. And melanin is the cause of this dark color.
So, in order to retard or slow down this process we need to restrict the amount of oxygen from the exposed flesh of the fruit. But remember, once this reaction starts or is in motion, subsequent reactions occur spontaneously – meaning deprivation of oxygen will not halt it. Thus, it’s important to implement measures to prevent browning soon after the guacamole is prepared – or more importantly once the avocado skin is broken (meaning that you should not leave cut or mashed avocados sitting around too long exposed to air).
Another way to retard oxidation is to add lime/lemon juice to the guacamole. Enzymatic browning occurs between the pH of 5-7 (don’t hold me to the exact number) in warmer temperatures (not freezing). So it is the citric acid in the juice that retards the enzymatic activity of the polyphenol oxidase by lowering the pH. This is the reason why people add lemon juice to avocados and often times apples to keep them from browning.
This is a very basic, short and simple explanation. I will not go further into this, since I can already feel your eyes glazing over. So the best thing to do in order to keep your guacamole green is to do both – restrict air exposure and lower the pH by adding lime/lemon juice.
I’ve kept mine in the refrigerator, in an airtight container with some lime juice, for five days. It was still perfectly green! I – in no way – recommend this. So do not attempt it at home! I just wanted to see if it turned dark (or if anything grew). I used to love watching things progress – especially in a petri dish – when I was young. I probably still do.
Try to eat it within a couple of days – EVEN IF you can keep it longer. Avocados, especially organic ones, are expensive. You don’t want to waste them!
Added 5/1/2012. I thought the following would be implicit in this post. But maybe they are not. So at the risk of being way too obvious, here are the assumptions I’ve made. First, I’m assuming you will not be consuming the guacamole within a few hours and that you want to store it for at least a day. Second, you don’t own a vacuum sealer. If you did, you don’t need to bother with anything else. Suck out the air, and you are done. Third, your aim is to keep it GREEN if possible – not greenish with brownish spots on top – although there is no foolproof method. Wow. I feel like I’m publishing a research paper, laying out my assumptions and limitations!
Keep in mind that although there are different means, the aim is the same: to restrict air exposure and lower the pH.
HOW TO KEEP GUACAMOLE FROM TURNING BROWN
- In order to keep your guacamole from turning brown, you would need to suffocate the air out of it (so to speak) to restrict exposure to air. Transfer the portion of guacamole that you will not consume immediately to an air-tight container. Glass/Pyrex-type of container with a locking lid is best. Don’t just plop it in there – fluffy with air. Try to really pack it in there. If you look in the image below, you will not see any big air bubbles on the side.
- Squirt some lemon or lime juice on top. Just in case it wasn’t clear: just a squirt people! Your guacamole will likely already have some lime or lemon juice in it. This extra squirt is meant only for the surface on top that may come in contact with air. Pour any excess juice out or dab it off. Cut a square of saran wrap that will cover the entire surface of the guacamole on top. Place the saran wrap on the top surface of the guacamole. Try to get it as taut as possible, pushing out any air bubbles. Alternatively, you can add a layer of sour cream or bean dip instead of saran wrap. It works in the same manner. This is the reason why in a layered dip, guacamole is never on top.
Although I used a bigger container in the images, you should use an air-tight container that JUST fits the guacamole. You want the lid to just touch the saran wrap pushing down on the guacamole and squishing out any air that is present on top. This is the reason why stores that sell fresh guacamole has it packed all the way to the top. (But even if you don’t, it works. You just have to be more mindful about packing it in and covering it with saran wrap.) I apologize in advance for stating the obvious; but refrigerate this portion you want to store immediately.
The image below was taken about a day and half after preparation – not a speck of brown.
* On a side note, leaving the pit in the guacamole ONLY helps insofar as it decreases the surface area that is exposed to air. The surface area of the guacamole that is covered by the pit will stay green, but not much else. So if you want to leave it in as a decorative measure, go ahead. But it will do very little in keeping the exposed areas of the guacamole green unless you will be consuming it within a few hours. Your guac should stay green (pit or no pit) for a few hours due to the lime juice that is likely in your recipe, provided it was added before the oxidation reaction (quinone formation) began.
I read your chemical explanation for the avocado turning brown, and….I really enjoyed it! I even got out my dictionary, which gave a poor excuse of a definition for ‘quinone’ : “…any of various quinonoid compounds…” and ‘quinonoid’: “resembling quinone…” I have had a horrible problem with my quacamole turning brown, even with drowning it in lemon juice, and now I think it’s because I didn’t seal it well enough. P.S. Wish you’d been around for high school chem (we were still using slide rules back then!). Looking forward to more chemistry in the kitchen “lectures.” Thanks!
Wow. Thank you for reading the entire post Sara! You must have been a great student 🙂 The reason why the dictionary gives a poor definition is that it’s hard to define in layperson’s term what quinones are in a concise manner. “Quinones are oxidised derivatives of aromatic compounds.” Wha?! It would take a lot more than a few sentences to do it justice. But no matter. As long as your guacamole doesn’t turn brown! Hopefully, you won’t have to drown your poor guac with lemon juice anymore 🙂
love the science behind the food! always an interest.
Thanks Andy! I was a bit apprehensive about this post due to the subject matter. I’m so glad to hear you liked it!
Good information! I love food science and seeing it spread.
There’s another variable you can control: time. It only takes a couple minutes to halve the avocados and mash them into the other ingredients (which can be prepared ahead of time). Do this shortly before serving and the enzymatic reactions won’t darken your door.
Gringos are so used to adding lime juice to guacamole that it seems it’s practically a rule north of the border. Not so much in Mexico. When guacamole is made without lime juice the subtle flavors of the avocado can really shine. The best guacamoles I’ve ever had were 1) in Mexico, and 2) made without lime juice. With lime juice that subtle flavor is masked.
JMHO.
Hi, thanks for coming by my site! Your method works fine as long as you will consume it right away. But if you want to store it, the enzyme will still inevitably turn the guac brown. Unless your other ingredients are acidic in nature and brings down the pH, there is no science that would support it keeping its color. Even in an acidic medium with lemon/lime juice, the browning will slow down, but will not stop – of course, unless you can suck all of the air out of it.
Enzymatic browning is something the food industry will love to control, but they haven’t found a silver bullet even w/ their $$$. So I wish it were so simple, but it’s not.
I totally love that you didn’t just glance over this! Thanks! 🙂
Mmmm avocados – delicious and healthful. Will be trying the wrap method next time i make it 🙂
Hi Vic! Just make sure to really pack it in. Any air bubbles are bad for guac storage. You can fluff it back up when you serve it. Hope it works out!
I don’t know how many times you’ve prepared guacamole, but as a mexican I’ve prepared, eaten and stored guacamole more times that I could count. I’m saying this mainly because of the part where you say that the pit doesn’t really help and I beg to differ… Theres an important difference that you’ll see if you want to refrigerate the guacamole for a day or 2 days tops. If you leave the pit, it will stay fine overnight and start to get brownish on top the 2 day. If you don’t leave the pit it will be all brown almost black the next day. I talk from experience of course, not science.
I was drawned to this article because I was curious to see if the autor would point out THE best way to help prolong the freshness of the avocado/guacamole. After a lot of techniques, the easiest way is to put it in an airtight container or a ziplock bag with a big piece of onion. It was incredible to see how much it helped just leaving there a 1/4 of an onion or so.
You should try it.
Hi José! Thanks for your comment. I am a big fan of guacamole, but I will submit that you’ve probably had it more times than I have. 🙂 I have tried the pit method many times; but apart from the surface that is covered by the pit (and the area immediately surrounding the pit), it hasn’t worked for me at all. But of course, I am talking about keeping it green without brownish spotting. And that would be impossible without restricting air exposure. If you don’t mind the brownish hue on the surface, there are many easier ways to get the job done. But with your onion in an airtight container method, I think we are basically talking about the same thing as a big piece of onion should cover most of the surface area, thereby restricting exposure to oxygen. Ziploc would also do the same thing, especially since it will stick to the guac creating a seal. So the reason behind why it would work would be the same – sealing out oxygen. But I will definitely try it.
The method I describe above is the best way (purely in my opinion) I found to keep guac green through my kitchen experimentation based on my science background. But I in no way am discounting other methods that may work for others! And remember that even though our physical methods may differ, the science behind it is the same. Thanks you for sharing your thoughts and happy eating!
Hey… great article; however, I have to admit that I read it for the same reason as Jose… I wanted to see if you’d suggest the pit method. I thought I was going to be disappointed, but kept reading… then you did mention it; although, your opinion didn’t agree with mine. My dad’s family is 4 generations from S. Texas (like North side of the river…). At one time, they had one of the largest produce and canning operations in Texas. Aside from that, my Grandmother was surrounded by great women and learned their cooking secrets (nice Baptist Church dinners, you know)… anyway, the pit method is what my family always used. It’s one thing to have some lime juice in your guac, but to saturate it doesn’t sound appetizing.
Perhaps I could get a government grant to set up a controlled experiment. Prove it, one way or another!
Thanks for at least giving the traditional methods a mention!
Hi Bill! I KNEW the pit thing would upset some! 🙂 If you are consuming it soon after, that would be perfectly fine. But this post was purely for storage. I’m definitely NOT suggesting saturating it or drowning it in lime juice. I hate a soggy guac as much as the next guy – probably more so. You are basically just squirting some juice on top & draining it or dabbing it off. If even that isn’t appetizing, seal the top with some sour cream, bean dip, or even chopped veggies (onions!) that you can just mix into the guac.
I think the food industry has already done plenty of research on this subject. They lose a lot of $$ due to enzymatic browning in general – not just avocados. There really isn’t a “foolproof” method unless you want to freeze dry it or some other crazy method. Thanks for the comment Bill. I always love hearing different experiences from different people. Maybe you can give me one of your grandmother’s recipes!
Very great tip. So cool!
Thanks LP!
wow this is really interesting! thanks a lot for that useful information, although I always add lime juice or vinegar to my guacamole
Thanks Beti! I assumed most people already add some type of acid to their guacamole. But I thought it would be cool and useful to know why. I’m so glad you found the info useful!
thank u so much…This post was really helpful Gomo..there have been times when I threw away the entire Guacomole which had browned..silly me ..I never tried to figure out why!
You’re welcome Kavita! I’m glad you found the post helpful!
Thank you so much for sharing! =)
Hey,
I chanced upon your blog because I was searching for a way to make guacamole without lime. I enjoyed reading it! You mentioned that lime only serves to lower the pH so as to prevent browning (oxidation). 2 questions:
1) If I am not concerned about browning, would it be possible to make the guacamole as you described without the use of lime?
2) In your description of the enzymatic browning, am I correct in understanding that avocado possesses both the enzyme and the substrate it helps oxidize?
Oh my gosh! I’m so sorry for the late response Litic! For some reason, I didn’t see your comment. It probably came in while I was on vacation & got lost in the comments.
To answer your question, it is a matter of personal taste. Some people don’t really like the taste of lime. Just skip it, especially if you are planning to consume it right away and not worried about browning. And yes, the “meat” of the avocado need only be exposed to oxygen to start turning brown. Hope you have a lovely week! 🙂
Great post! I did actually read it and enjoyed reading. I started liking avocado probably 2 years ago, so it’s not that long, but if i make guaca. then it’s eaten in less then 30 minus lol! I do add lime or lemon juice bit because of the color and bit because it tastes better. Anyhow thank you for sharing your knowledge and experiment!
Thanks Sandra! We finished ours tonight too. I usually make it the night before tho. Lucky for me, this works like a charm! 🙂 I hope you had a great weekend!
Thank you so much.
You’re welcome Cathy! Hope it worked for you!!! 🙂
Stumbling across this post was just a random internet encounter por moi, but seeing that you take such a keen and genuine interest in thoughts of your readers, I felt compelled to offer a piece of advice (more of a request, actually): don’t be afraid to allow intellect and technical detail in your writing! Please! 😉 When I saw the words “polyphenol oxidase,” I was genuinely thrilled, and there have got to be others out there like me. Think about it: fifty-thousand cooking blogs are going to tell you to not expose your avocados to air, and this is obvious. Borrrring. But I would bet cold cash that yours is the only one that details the chemical reaction that takes place. Which is more interesting? That you have the ability to merge your culinary and scientific skills totally unique, and totally bad-ass. Maybe interesting chemistry could be a regular component of your posts? I bet people would love it.
MY takeaway? That the final oxidization by-product is melanin. When you look at your disgustingly darkened avocado, you’re seeing a human suntan? Wild.
Thanks for doing just a little bit to keep the world smart. Keep it up, fo’ realz.
Thank you so much for your thoughtful comment; it means a lot to me. I’m genuinely happy that the post was helpful in anyway. I’ll take your words of encouragement and plan my next science post accordingly. 😉 Also, thank you for the humor in your comment. It was much need this morning. It’s one of those 3-mugs-to-get-things-going kind of morning. 🙂
I am a RN and I also loved every bit of the scientific explanation and chemical reactions related to food and cooking. I have always found that if I know the “why” I can remember facts so much easier.
I agree with the others who would love to see more of this!
Thanks for the info!
Thank you so much for your comment Jules! I’m so glad that you found the post enjoyable. Due to encouraging words like yours, I am planning to do another science-related post in the near future. Thanks again and have a great weekend! 😀
Hi. Thank you! This was fantastic! I appreciated the chemical process explanation as well. (And no, I am not a chem major or nerd.) I simply appreciate knowledge. Thanks again! This was very helpful.
Thank you for your kind words! When I first wrote the post, I thought no one would read it. I thought most readers would just scroll down to the bottom for instructions. I’m just so appreciative that people are actually reading the whole post and finding it helpful. 😀
I read the whole post it’s so interesting and informative so glad I find your blog guess it will be my new favorite 🙂
Thank you so much K.A! You really made my day. I’m so glad you found the post informative. I really enjoyed writing it. 😀
wow, I’m reading this article so long after you published it! But thank you so much for such an informative article with all the sciency, chemistry stuff. I’m not a huge fan of chemistry but it’s always nice to know how everything works. This is the closest I’ll ever get to actually enjoying organic chemistry 😛
For some crazy reason, avocados in Sweden are horrible, horrible, horrible. When you think that they’re ripe enough to be eaten, they’re always either rotten or only half ripe. And when you’re a Cali girl at heart, you need your guac. Sometimes I’ll slice open an avocado, sprinkle it with a bit of salt and there would already be browning after three minutes or so. It’s just insane to me!
But I’m definitely going to try to use the air tight method. I’ve used the lime/pit method and it’s worked with limited success. The comfort of warm, cheesy carne asada fries immediately after lab… you will happen!
Thank you Hannah, I’m so happy to hear that you enjoyed the post! It’s always nice to know why things work the way they do right? 🙂 Hmmm… Where do the avocados come from in Sweden? Even here, avocados aren’t so great during certain months; they don’t quite soften as should. But I have to admit, most of the time, they are pretty great and creamy. I would love to send you some Avocados, but they will probably rot by the time they get there! 🙂 Carne asada fries? Count me in! Hope you are having a great weekend!
Enjoyed the article
Though I have some friends from Mexico and all of then say u.s style guacamole is totally different. Guacamole down in chihuahua, Mexico is made from simply avacados and salt. They occasionally stir in some tomatoes and onions if they use it for dips…. But guacamole down there is used more like mayonnaise is here.
Anyways! Thank you for the tips on how to store, though the lime is unnesscary. If you put a 1/4 inch of water on top and pour it out when you are ready to eat it again it works great too!
The guacamole does not absorb the water because of the density of avacado. 🙂
Hi Linsey~ By adding water on the top, you are basically doing the same thing (keeping air out and preventing oxidation). There are many ways to achieve this, but the science behind it is the same. And lime is just another way to prevent, well more like slow down, oxidation.
You are right! I think most international foods here in the U.S. is changed a bit or a lot to fit the palates of Americans. I notice the same about Korean food. I hope you’re having a lovely weekend!
Very happy with what you said it made a lot of sence because you took the time to tell us about the facts behind it. I just made myn guac look almost identical to the picture you had up for storage I really hope I did it correctly hahaha. We’ll see when I get home from work tomarrow. Again thank you so much other posts didn’t explain it very well.
Thank you for your comment Mike. I’m glad you found the post useful. Have a great week!