On the top floor of Angola’s tallest building, overlooking the bay of the capital Luanda, a relatively unknown bottle of Benfeito Portuguese wine sold for a record $21,600 at an auction.

In Sao Paulo, Brazil, a 2000 Barca Velha red, produced more than 5,000 miles away from the steep, rocky vineyards of Portugal’s Douro Valley, costs 2,400 reais ($1,175) at Restaurante A Bela Sintra — more than four times its cost at Portuguese retailer Winept.com. It’s often sold out.

“Portuguese wines are making a comeback,” Frederico Falcao, president of Portugal’s Vine and Wine Institute, said in an interview. “Part of the reason is that consumers in emerging markets such as China, Angola and Brazil are evolving and buying more old-world wines.”

Wine exports from Portugal, including port and table wine, rose 7.6 percent in the first 11 months of 2012 to 648 million euros ($862 million) from the same period a year earlier, according to the country’s National Statistics Institute. Portuguese wine sales are boosted by demand from the former Portuguese colony of Angola, China and some South American countries.

One of the biggest challenges facing local winemakers is not being able to increase output fast enough to meet growing demand from abroad, said Alexandre Soares dos Santos, chairman of the Jeronimo Martins retailer that owns a supermarket chain in Portugal and discount stores in Poland.

“If we want to be serious about increasing our exports then we need to produce wine on a much bigger scale,” he said.

That means winemakers need to merge and invest in state-of- the-art equipment to crush their grapes instead of treading them underfoot in large vats called lagares, said Jose Hermoso, an analyst at the International Wine & Spirit Research.

“The fact that most of the wine companies in Portugal are family-owned may work against further consolidation but it has to happen,” Hermoso said in an interview.