How do I know when my avocado has gone bad, and how can I keep it fresh?

Question

I am a big fan of avocados but I usually don't eat a full one in one sitting. I usually cut them in half, leave the pit in the side I don't eat, and use the other half. In a day or two, when I come back to the uneaten portion of avocado - it is usually black and doesn't look good.

How can I recognize whether my avocado has gone bad or not? (besides blatant mold)

I usually put whats left of the avocado in a bag in the fridge and keep the pit in. Are these best practices to extend the life of my avocado?

Answer 1

An avocado will keep a few days in the refrigerator after it has been cut. The cut portion will turn brown/black due to oxidation, you can just cut that off, it is not harmful.

From California Avocado Commission to keep the avocado from discoloring sprinkle it with lemon/lime juice or vinegar and wrap tightly in plastic wrap or place in an airtight container.

From thekitchn storing a cut avocado with a piece of cut onion in an airtight container will stop the oxidation.

I don't know why this is, but I suspect that it has to do with the sulfur compounds that the onion releases. This is the same sulfur that makes you cry when you chop onions, but it is also used as a preservative. The onion's smell and taste don't seem to transfer to the avocado, as far as I can tell. But I'm not overly sensitive to onions, so you may want to check this out first if you are.

When not to use, from WebMD

if your avocado's flesh has become very dark or the flesh has become stringy you should avoid eating it, particularly if there is any sign of mold. Avocados have a very high fat content, so they oxidize and become rancid very quickly at room temperature and will need to be thrown away.

Answer 2

I've found that the best way to extend the life of a ripe avocado is:

mash it up,
put it in a plastic container,
flatten it out a bit,
cover it with an inch of water,
and finally put the lid on the container and put it in the fridge.

It will keep for a few days like this. The water will seal the air out. After a couple days you may have to scrape off the top layer of avocado.

Someone may know a better way but besides seeing that the avocado is bad (which should suffice for most cases) you have to feel it. If there is very little resistance then it's probably bad. Cut it open and see.

Answer 3

For less surface area to go black, try cutting in half (equal mass-wise) vertically; a bit of stone will peak out. I blot dry with paper towel and that seems to prevent blackening; goes leathery instead.

If you must bag, keep a dry paper towel in too; condensation is unkind to ripe avocados, cut or uncut.

Answer 4

Brush the exposed avocado flesh with vitamin C, a tablet dissolved in water works fine as long as it's reasonably pure. Store the avocado in a sealed Tupperware container in the refrigerator.

Browning is caused by harmless oxidation, it's fine to eat or to cut any darkened flesh away. Black, moldy or stringy avocado should be tossed.

For a write up of experiments on the subject, see Browning Avocado Experimentation.