Why do avocados go brown so quickly?
If you’ve ever made guacamole, you’ve likely noticed that raw avocado quickly turns into an unappetizing brown mess. That’s because of the same chemical process that causes apples and other fruits to brown—it’s just that in avocados, the process moves very quickly.
Here are the basics: When you expose an avocado’s flesh, an enzyme called polyphenol oxidase helps to convert phenolic compounds into quinones. This eventually produces polymers called polyphenols, which give the flesh a brown color.
To put it another way, oxygen is the enemy. It starts the underlying chemical process, and once it starts, it doesn’t stop.
While you can’t stop an avocado from browning entirely, you can slow the process.
The most common trick is to add lemon juice. Lemon juice boosts the acidity, slowing the enzymes and preventing the browning process. But this only works if you use enough lemon juice to preserve the entire avocado—exposed sections of the fruit will still brown.
You can also cover the avocado in a tight cling film. This prevents the oxygen from contacting the fruit, which slows the reaction.
You can also use red onions to stop avocados from browning.
For this method, you’ll simply small-dice a red onion and seal it in an airtight container with the avocado. The fruit should touch the onion; for best results, add in the pit on top. Again, the onion’s acidity staves off the enzymatic reactions, giving you more time to enjoy your fruit.
Of all of the methods listed here, the red onion trick is probably most effective—but it can flavor your avocado. That’s not such a big deal if you love onions or if you’re mixing onions into your guac, but it might be a dealbreaker for some readers.
By understanding the browning process, you can also preserve uncut avocados.
The browning process begins occurring as soon the avocado is plucked from the tree, but by limiting oxygen exposure, you can preserve the fruit. As soon as your avocados are ripe, wrap them in cling film and store them in your refrigerator.
What if you’ve got some unripe avocados that you’d like to ripen? Place them in a brown paper bag with an apple or banana. This works because apples and bananas contain ethylene, which triggers the ripening process. By enclosing the different fruits in a single bag, you trap in the ethylene, and your avocados 
Once you understand the basic chemistry behind the ripening process, you can easily store and use avocados without ever dealing with a sludgy brown mess. Oh, and if you’re looking for more avocado hacks, just know that some people are drinking lattes out of the fruit.Imgur