Grape growers simply created a promotional stunt to sell more grapes, and ended up creating a tradition that's lasted for decades and has become an integral part of the Spanish culture!
When I was studying abroad, my Spanish professor told us that Spain has the best wine in the world. Though I think he's biased, there is some validity to the statement! Spain is a huge producer of grapes and wine, particularly rioja wine in the north. In the (aptly named) region of La Rioja, wine is one of the biggest aspects of their economy. There are lots of bodegas (wine cellars) around the region that offer tours and wine tastings. Towns in La Rioja even have festivals celebrating wine, one of which includes a food fight...but with wine!
