Depending on the variety, avocados can be round or pear-shaped, green or black, and small or large. Avocado skin is usually rough. The flesh, when ripe, is soft and buttery. 

It is a climacteric fruit, which means it continues to ripen after harvest. Hass avocado is the most common and is available year-round.

If you are going to use it immediately after purchasing it, choose a ripe one with black skin that yields to a little bit of pressure when squeezed. 

Avocados with green skin that are very firm are not ripe and should rest for a few days before eating. 

If the skin is dark and wrinkled, or has dents or soft flesh spots, it may be overripe and unpalatable to eat.

Related articles: Abundance of avocados expected in the U.S. market this summer

Keep them fresh

Avocados are sometimes sold with hard, unripe flesh, which will often ripen in a few  days. You can leave the fruit at room temperature or expose it to direct sunlight to accelerate ripening.

You can also place the sealed avocado in a paper bag with a banana; the ethylene gasses from the banana will accelerate ripening. 

The flesh of avocados is notorious for turning brown quickly once exposed to air, which is called enzymatic browning.

Although unappetizing to the eye, the brown flesh is perfectly edible. Still, there are tips for slowing or reducing browning after cutting:

• Coat the flesh with lemon or lime juice.
• Wrap tightly with cling film or place in an airtight container and store in the refrigerator to reduce exposure to oxygen.
• Store an avocado half with some sliced onion in a sealed airtight container, as the sulfur compounds in the onion help preserve the avocado.

Unripe avocados should not be placed in the refrigerator, but once they are ripe it is okay to do so.

Did you know?

According to Harvard University, half of this fruit has more potassium than a medium banana, 487 mg of potassium versus 422 mg of potassium, respectively.

Ripe avocado puree is sometimes used as a face mask because of its high content of moisturizing oils and vitamin E.