Once the tomato pulp is flushed, the ground is clean due to the acidity of the tomato.
The festival is believed to have originated in 1945 when a group of young men staged a protest in the town's main square during the parade of gigantes y cabezudos.
The gang grabbed tomatoes from a nearby vegetable stand and used the fruit as weapons, forcing the police to intervene and break up the fight.
The rules of the game are simple: squash your tomatoes before throwing them; only tomatoes can be hurled; give way to lorries; don't rip T-shirts and stop when you're told to.