To keep leftover guacamole from going brown, follow this tip!
Put your guacamole in a small bowl that is nearly filled to the top. Use a knife to even out the top of the guacamole and then, put a very thin layer of water on top and cover it tightly with plastic wrap or a secured lid. When you are ready to eat it (within 2-3 days max), pour off the water and voila – it’s ready to eat – and it’s not brown! The reason it becomes brown is due to oxidation and the water keeps the oxidation process it from occurring.