Vegetables for vitality: avocados

Healthy, unsaturated fats give this tropical fruit (it is not a vegetable) its creamy texture and nutty flavour. Read on to learn more about this superstar fruit.

Called "midshipman's butter" by British seafaring crews over a century ago, avocados taste delicious simply mashed on toast. Avocados are used mostly in appetizers and salads.

Packed into a quarter of an avocado:

• about 81 calories
• a significant amount of vitamin E, which slows the aging process and protects against cancer
• monounsaturated fats, which help lower blood levels of LDL (bad) cholesterol
• lutein, which protects against cancer and eye diseases
• folate to help protect against heart disease
• glutathione, an antioxidant that protects body cells from damage
• beta-sitosterol, which helps block absorption of cholesterol in the intestine
• magnesium to help with muscle function and energy metabolism
• potassium to keep electrolytes in balance

Season

Fresh avocados are available all year, because they don't start to ripen until they are cut from the tree. Farmers can wait months to harvest an avocado crop so that they always have fresh ones to go to market.

What to look for

Variations in size, colour and skin texture depend on the variety and where it is grown. No matter what type of avocado you buy, look for heavy fruit and avoid any that is bruised or has sunken spots in the skin. A ripe avocado will yield to gentle pressure from your hand.

Storing

• If you buy an unripe avocado, it will ripen at room temperature over the course of a few days. To speed up the ripening process, place the avocado in a brown paper bag. Store at warm room temperature for a day or two or until the avocado yields to gentle pressure from your hand.
• You can ripen a cut avocado this way, too. The cut surface will eventually discolour but this can be delayed by coating the cut surface with lemon juice and then covering it with plastic wrap. Ripe avocados can be stored in the refrigerator for four or five days. Don't store unripe ones in the refrigerator because they will never ripen properly.
• If you find yourself with an excess of ripe avocados, peel and stone the fruit and purée it with a little lemon or lime juice to limit discolouration. You'll need about 10 millilitres (two teaspoons) of juice for each avocado. Then pack the purée into a covered plastic container, label with the date and store in the freezer for up to four months.

Preparation

• To peel an avocado, first slice it into quarters or halves lengthwise, cutting to the large centre seed. You can twist the cut avocado to separate the halves. Remove the seed with a paring knife if it doesn't lift right out. If the avocado is ripe, use your fingers to peel back the skin. Otherwise, use a paring knife.
• Always rub or sprinkle cut avocado with lime or lemon juice to prevent discolouration. This inevitable browning doesn't affect the flavour or nutritional value, but it does make the avocado look less appetizing. Cover mashed or puréed avocado with two layers of plastic wrap applied directly to the surface. The convenient belief that pressing the seed into mashed avocado will prevent browning is, unfortunately, not true.