If you want to keep your guacamole looking fresh and vibrant, it's important to avoid exposing it to air. When the avocado's cells are exposed to oxygen, they start to oxidize and turn brown. To prevent this, spread the guacamole into a flat layer in your storage container and cover it with a layer of plastic wrap, making sure the plastic is in direct contact with the surface of the guacamole. Then, pour about half an inch of water over the plastic to create a protective barrier. This simple trick can help your guacamole stay green and fresh for up to 2 days.