Minecraft wiki entry for Item, associated text: If an item that does not become a block is dropped, it becomes an entity represented by a sprite that floats above the ground for 5 minutes in a loaded chunk before despawning, unless the player walks over it to pick it up before it despawns, it is picked up by a mob, hopper or minecart with hopper, or it is destroyed by fire, lava, cactus, or explosions.