Choose avocados according to when you plan to use them. A firm fruit may still be unripe; a ripe avocado yields gently to light pressure in your palm. Color varies by variety: Hass generally darkens as it ripens, so do not treat dark skin as a sign of an unripe fruit.
Ripening. Ripen firm avocados at room temperature. Placing them in a paper bag with an apple or banana can speed ripening; check daily. Refrigerate ripe fruit to slow the process.
Cut avocados. Before cutting, wash the skin under running water and use a clean knife. Brush the remaining cut surface with a little lemon juice, wrap tightly or place in a covered container, refrigerate, and use promptly. Lemon and reduced air exposure delay browning but do not guarantee safety. Leaving the pit in does not protect the entire exposed surface; do not store avocados submerged in water.
Common mistakes. Relying solely on skin color, leaving ripe fruit on the counter for long periods, and leaving cut fruit exposed can increase quality loss. Do not eat rotten or moldy produce.