Delta Air Line's master sommelier Andrea Robinson opened up bottle after bottle of white and red wine from France, Italy, Australia, the U.S. and other parts of the world.

As she tasted them Monday, a blue bucket sat on the table next to her. It was there so she could spit out each sip, ensuring she didn't get tipsy and could distinguish between the different wines. By the time she's done in the next few days, Robinson will have tasted and smelled roughly 2,000 bottles.

The delicate work of a sommelier has become more important as U.S. airlines fight for premium passengers willing to shell out up to thousands of dollars to fly business class on international and transcontinental flights. The idea isn't to make money on the wine — the passengers in those seats drink for free — but rather to keep those customers coming back and encourage their well-heeled friends and co-workers to join them. Other airlines including United Airlines and American Airlines also work with wine experts to help them choose what to serve on their flights.

And there's a market for it: According to the International Air Transport Association, through the first four months of this year, there was an 8.5 percent increase year-over-year in premium passenger traffic, which includes business class and first class seats. Those seats are among the most pricey and profitable for airlines. The trade group expects fuel costs to weigh on premium traffic, and stronger growth in the second half of the year will depend on how well the economy holds up.

Robinson's task is to choose 30 labels for Delta, which is based in Atlanta. The wine and champagne will be served in Delta's BusinessElite class cabins in 2012. The world's second-largest carrier expects to order some 1.6 million bottles for the service. The still wines Robinson looks for range from a retail price of $25 to $30 a bottle, while dessert wines will run $30 to $35 a bottle and the champagne will run $45 to $50 a bottle.

"If it costs $20, it has to taste like $40. That's what I'm aiming for," Robinson said.

She is looking for wines with a distinct taste that will come through when sipped at 30,000 feet by bankers and vacationers alike, because passengers' sense of taste and smell can be diminished when in flight.

Delta's domestic coach passengers can buy glasses of wine, though the selections won't be as chic and won't get the same special attention from Robinson. Coach passengers on Delta international flights get wine for free.

Sommeliers are also working with other airlines.

Doug Frost, a Kansas City author who writes and lectures about wine and also is a master sommelier, is the wine and spirits consultant for United Airlines. He helps select tens of thousands of cases of wines and spirits each year for the carrier. Ken Chase, a Canadian classically trained wine merchant with an international reputation, does wine selections for American Airlines. According to the airline, Chase selects fine wines for various routes paying close attention to menu parings, as well as the ethnic, cultural, seasonal and stylistic differences of each destination.

Delta also is mindful of the destinations it serves when it selects wines. Some of the offerings on Robinson's taste menu came from Chile and Argentina. Delta has a big presence in Latin America.

The selection of wine, though, isn't the only thing that's important. So, too, is the flight attendants' knowledge of the offerings so they can answer business class passengers' questions. Delta is offering wine training for flight attendants.

Julie Pearson, who has been a Delta flight attendant for 23 years, attended Monday's wine tasting. The 44-year-old works in the BusinessElite cabin on the airline's Boston to Amsterdam route. Some passengers will know exactly what they want, while others have questions and enjoy the ability to taste the different wines on board before making a selection.

"A good sign for the flight is when all my wine glasses are dirty — and that happens a lot," Pearson said.