Avocados inevitably turn rusty brown once the flesh is exposed to the air, due to a chemical process called oxidation. There are a number of ways to stave off the damage. For instance, if you’re using your avocado in a sandwich, mash the flesh with a couple of tablespoons of mayonnaise. Then press plastic wrap directly onto the surface of the mixture. This is a preventive measure, not a cure. Browned avocado flesh is not spoiled or harmful. If brown patches start to appear, give the avocado mixture a stir. More ways to limit discoloration, pg. 241 in 12,167 Kitchen and Cooking Secrets.
