(Wine-Searcher) - Sales figures indicate that box wines are becoming increasingly popular.

It's 50 years since the first box wine was created by Australian producer Angove and, while some wine drinkers may scoff at them, box wine brands are making millions; the category now represents almost one in five liters of wine sold in the US.

To mark the April anniversary, Nielsen gathered off-premise sales figures for Wine Searcher and they show a market that's growing and growing. The category has doubled its share of the US wine market since 2009 and, by 2014, box wine sales represented 7 percent of all wine by value and 17.5 percent of all wine sold by volume.

"People have the impression that the box wine market has seen its day," Danny Brager, Nielsen's senior vice-president of beverage alcohol practice told Wine Searcher. But they're wrong, he explained.

The three-liter box wine market has been experiencing double-digit growth in recent years, reported Brager, although the five-liter format, purchased mainly by the over-55s with low incomes, is slowly declining.

There are more wine brands sharing in the success of the three-liter category; in 2010, only two box wine brands enjoyed sales of more than a million dollars. In 2014, that figure increased to 16 brands with another five nearing the million-dollar mark.

While most people only spend $16-20 on a three-liter box – equivalent to $4-5 per 750ml bottle – there are a few brands attempting to break the $20 barrier, and sales in that segment (3 percent of the market) has grown 74 percent in the last year.

However, only 5 percent of wine buyers in the US buy box wines, says Brager. "The challenge is convincing consumers that the quality is good and if you buy and drink wine you are going to get the same experience as drinking out of a bottle."