“We’ve boosted our exports significantly, but probably too rapidly, so that we’ve now got the wrong price pyramid, with a lot of wine sold very cheaply,” said Rafael del Rey, the director of the Spanish Observatory of the Wine Market, an institute that researches and promotes the country’s wine.

In recent years, France and Italy have jostled for the top spot as the world’s biggest wine-producing nation, with Spain third, well ahead of countries like the United States, Chile and Australia.

The bulk producers in Castile-La Mancha are understandably proud of the state-of-the-art irrigation, harvest mechanization and storage systems that they put in place, with help from European Union subsidies. Coupled with relatively low labor costs, their infrastructure has allowed them to lower the price of their wine to half that of France’s.

But Mr. del Rey offers a telling comparison between Spain and Italy. In 2000, both countries exported their wine at the same average price, 1.41 euros per liter. By 2014, Italy was selling its wine for an average of €2.5 per liter, or $2.78 under the current exchange rate, while Spain’s sold for €1.17, or $1.30.

In that period, Italian exports rose 15 percent in volume and Spain’s 154 percent. But Spain’s export revenue reached only €2.6 billion, about half the value of Italian exports.

Spain’s bulk wine has displaced Italy’s on the European market, particularly in France. Spain now sells about 500 million liters to France, 90 percent of which are bulk exports, at an average price of four-tenths of a euro per liter.