Recently, I wrote an article about whether raisins used to have seeds. Whil I was writing it, I was thinking, why are raisins brown? In some part, raisins are brown for the same reason apples, potatoes, and avocadoes turn brown after you cut them open. It’s all due to a compound called polyphenol oxidase (PPO) combined with enzymes. With raisins this “enzymatic browning” is a good thing. It’s not so good when it affects your guacamole. Despite our best intentions, we can’t always eat all the guacamole we make at once. It turns a yucky brown color so darn fast, though! Is there anything we can do to stop guacamole from turning brown?
What Causes Apples, Potatoes, and Avocados to Turn Brown?
When you cut open an apple, potato, or avocado, the inside of the cells can come into contact with the air. The polyphenol oxidase (PPO) in the cells reacts with oxygen in the air to form melanin pigments. Wait, I know. You didn’t come here for slop. You want a way more in-depth explanation.
When the PPO in the cells are exposed to oxygen, they react with phenolic enzyme compounds in the fruit (or root) to form quinones. These quinones polymerize quickly into melanin pigments, a process called enzymatic browning, and the result is an offputting brown color. The presence of peroxidase may also initiate this process. 1 While the result is safe to eat, the taste and nutritional content of the food is also affected. This process also occurs in some seafood like shrimp, crab, and lobster.
Enzymatic browning is often a good thing and not only in raisins. It’s good in tea, chocolate, and barley malt for beer. It’s beneficial in dried fruits, spices, and certain cheese rinds. It’s awful in guacamole, resulting in a schloppy green-brown mess that nobody wants to eat.
There are several ways to stop enzymatic browning from happening:
Heating: heating denatures the phenolase enzymes and stops the oxidative reaction from occuring. when you cook potatoes or apples quickly, you don’t have to worry about them turning brown due to PPO reactions. They may turn brown due to another reason, the Maillard reaction, which is a non-enzymatic browning process involving amino acids, and caramelization due to sugars.
- Acid: The addition of an acid can slow down the oxidative process. Lemon juice, which is typically used for apples and pears, contains citric acid. This acid slows down enzymatic browning in a few ways. It changes the pH which affects the function of the enzymes, and it is an antioxidant, reducing the available oxygen to catalyze the reaction. Other acids, like vinegar, lime juice can also work to some extent. Lemons juice or vinegar can be mixed with water to make acidulated water, if needed. Other acids can be used, as well, like citric acid powder dissolved in water, as well as oher acidic fruit juices like grapefruit, cranberry, or Concord grape juice.
- Salt: Coating the fruit or potatoes in salt can slow down the oxidation process to some extent. Salt damages the enzymes.
- Sugar solution: Coating fruit in a sugar solution helps keep oxygen from reaching the reactive compounds in the plant cells.
- Immersing cut potatoes in water: Placing cut potatoes in water helps slow down enzymatic browning by sequestering the potatoes from oxygen in the air. However, this does not completely stop the process.
Unfortunately, with guacamole, all of these methods are limited in utility, to say the least. You can’t just keep adding lime juice (or lemon juice) to guacamole to stop browning. You’ll ruin the taste. You only need a little lime juice for a perfect guacamole and we already know the amount of lime juice we use is not enough to prevent browning. Likewise, you can’t add too much salt. You can’t cook it. You can’t coat it with a sugar solution. You can’t immerse it in water. Eh…let’s just give up and eat our guacamole quickly! Maybe the pit is like a bezoar stone.
The Magical Brown Preventing Avocado Pit
Placing the avocado pit in the center of the guacamole is claimed to stop browning Yeah, no. This does absolutely nothing. There is nothing about an avocado pit that will react with PPO or any other responsible compounds to prevent browning. Now, perhaps, the part of the guacamole that is under the pit will not turn brown, if the pit prevents oxygen from getting to that part. Small victory.
But wait! It’s all about the oxygen. Stop the oxygen from coming into contact with the exposed cells and you can stop the browning. We have the technology. We can do this!
How To Stop Guacamole From Turning Brown
Now, of course, when you put leftover guacamole in the fridge, you seal it in an airtight container with a tight lid. Most likely, you use a plastic container. That’s blocking the oxygen, right? Yes but there is already air inside the container, trapped inside with the guacamole. The next day, that guacamole is still dead.
The solution is so simple that you’ve probably already thought of it. You have to make sure there is no trapped air inside the container, or at least no air between the guacamole and whatever seals it away from the air.
One method is to cover the surface of the guacamole with plastic wrap, being sure to completely cover it and not trap any air between the plastic wrap and the guacamole. Then, also seal the container it’s in.
An even better solution is to use a sealable container that is small enough for the guacamole to fill it to the very top. If necessary, use several small containers, filled to the brim, instead of one large. This way, when you place the seal on the container, there is not any trapped air inside. Better yet, combine both methods to make doubly sure you completely sequester the dip from oxygen. Fill to the top. Put plastic wrap on top. Seal the container. The result will be that your guacamole is still green the next day. After that, you’d better eat it, though. Nothing lasts forever.
There is one other method you could try. Instead of using plastic wrap, you could place a small amount of water on top of the guacamole. The water will not mix into the guacamole due to the high-fat content and will create a seal against oxygen. Some say this works, like Faith Durand at The Kitchn. However, I think the above method may work longer, as water does not completely prevent oxidation. Oxygen can still get through water. This is why immersing cut potatoes in water does not work forever.
How Do They Keep Packaged Guacamole From Turning Brown?
You’ve probably seen or even purchased prepared and packaged guacamole from the grocery store. One way manufacturers keep this guacamole from turning brown is through vacuum packaging. If you have a food saver vacuum sealer, you could do this too. You don’t have to put guacamole into plastic bags to do this. There are sealable plastic containers available with a pump valve on top. This is probably the ultimate way to store guacamole at home but it too will not completely stop enzymatic browning. As I noted in this article, when vacuum sealing cut fruits like avocado or apples to prevent browning, only do it for a short time. Do not attempt to “preserve” cut fruit by vacuum sealing. It will not work.
- Food vacuum sealer keeps food fresh up to 5x longer compared to ordinary storage methods and prevents freezer burn to help you waste less and stretch your food dollar further
Prices pulled from the Amazon Product Advertising API on:
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.
Vacuum sealing is not the only method manufacturers use to protect packaged guacamole, though. High-pressure treatment is also used by some guacamole makers. The pressure denatures the enzymes, preventing them from reacting. When both methods are used, vacuum sealing and high-pressure treatment, packaged guacamole can be kept in the fridge for several weeks without any browning.
You’ll also notice that packaged guacamole containers are filled to the top and the ingredients may include other acids, in addition to lime juice, such as citric acid and ascorbic acid.
- Y. Jiang, X. Duan, H. Qu, S. Zheng, Browning: Enzymatic Browning, Editor(s): Benjamin Caballero, Paul M. Finglas, Fidel Toldrá, Encyclopedia of Food and Health, Academic Press, 2016, Pages 508-514, ISBN 9780123849533, https://doi.org/10.1016/B978-0-12-384947-2.00090-8.