Like most fruits, avocados do not ripen until picked, so fresh ones will be as hard as rocks. Look for an even unblemished texture, uniformly hard or soft over its entire surface and those that feel heavy for their size. Avoid any with bruises or soft spots, and those with a hollow between the flesh and skin. Shake the avocado to test...if the pit is loose, move on to the next one.
The flesh of ripe fruits will yield when pressed gently.
However, ripe fruits bruise easily with excessive handling in the markets, so it is best to ripen your own at home. Of course, this means proper planning, giving yourself 2 to 5 days in advance to insure they are ripe for your use.
To ripen, place the avocado(s) in a brown paper bag and store at room temperature for 2 to 5 days, away from direct sunlight. The addition of an apple or banana to the bag will hasten the ripening process. Do not store unripened fruit in the refrigerator. After being chilled, they will never ripen properly. Once ripe, they can be stored in the refrigerator, unpeeled, for up to two weeks.
The flesh of the avocado quickly begins to darken when exposed to the air, so it is important to work quickly with the meat once the avocado is cut. The addition of an acid (lemon is usually the acid of choice) retards the darkening process.
To get to the avocado meat, slice it lengthwise all the way around to the pit.
Then gently twist each side in an opposite direction to separate halves. The pit should remain in one side. Slip a large spoon in between the skin and the meat and scoop out the tender flesh or peel and slice.
Sprinkle pieces with lemon juice to retard browning or mix in 2 teaspoons of lemon juice to each cup of mashed avocado.
Wrap tightly to store in refrigerator for 1 to 2 days.
If you need to prepare peeled avocados a few hours in advance, wrap the pieces in paper towels soaked in lemon juice and wrap tightly with plastic wrap. If darkening does occur, simply gently scrape or cut off the discolored area.
To freeze avocado, puree flesh with 1 tablespoon of lemon juice per 2 avocados, and place in a tightly-closed container with the air removed. Frozen avocado can be kept 3 to 6 months at 0 degrees F.