Avocado stays fresh for at least 3 days after being cut. However, the green outside oxidizes and begins to turn brown. You can eat brown avocado, but it doesn’t look as appetizing as when it’s bright green. To stop the oxidization process, you need to store the avocado with as little air near it as possible. You can press plastic wrap down onto the avocado to help. You can also coat the top of a cut avocado with fresh lime juice. Keep it in the fridge.