(WineSpectator) - Two in-depth looks at the American wine market offer a glimpse of how young drinkers, now the largest segment of wine drinkers, are driving trends.

They grow up so fast. Just before midnight on Jan. 1, 2016, the youngest member of the Millennial generation turned 21 years old. Now 79 million strong and between 21 to 38 years old, this cohort consumed 159.6 million cases of wine in 2015, according to the latest report on the U.S. wine market from the Wine Market Council. That's more than any other generation and 42 percent of all the wine drunk in this country last year.

For years, industry observers have said that Millennials could potentially have a big impact on wine, but not just yet. Now that the moment has arrived, what do their preferences mean for the American fine wine market's next decade?

Settling Down Means Trading Up

Every year, the WMC surveys mostly "high-frequency" drinkers (1,200 respondents in 2015), defined as those who consume wine several times a week. That segment drinks roughly 90 percent of wine consumed in America. In the 2015 survey, Millennials accounted for 30 percent of the high-frequency drinkers WMC spoke with, Baby Boomers 38 percent and Gen Xers 20 percent. Marketing firm Nielsen also tracks the wine market each year; their latest data reflects numbers reported by the majority of off-premise (i.e. stores rather than restaurants) retailers in the country.

Perhaps the most important development of the past five years is that the "older Millennials"—those the WMC categorizes as 30 to 38 years old—are more settled in life and more confident in their tastes. "Wine drinkers are beginning to sort themselves out," said John Gillespie, president of the WMC, at a presentation of his findings in New York last week. "It's the self-identification of, 'Yeah, I'm a wine person.'"

That makes their drinking habits a little more reliable to assess. Looking back at five years of WMC and Nielsen research, a picture emerges of which developments in wine were fads and which seem to be lasting.

When it comes to price, as Millennials have grown up, they've grown more willing (and able) to part with money for a good bottle of wine. WMC surveys found that 17 percent of all Millennial wine drinkers bought a bottle costing over $20 in the past month, compared to 10 percent of all drinkers and 5 percent of Baby Boomers.

That trend of trading up mirrors the U.S. wine market as a whole: 37 percent of high-frequency wine drinkers purchased at least one bottle of wine over $20 per week last year—double the number in 2010. Nielsen's study of off-premise sales bears this out: The average retail bottle purchase in 2011 was $6.31; in 2015, it was $7.81. Nearly 17 percent of wine sold retail in America is priced $15 or more.

Your Go-To Wine? Variety

But younger drinkers don't show any signs of settling down when it comes to the type of wines they drink. It's not an exaggeration to say the Millennial American consumer has the most varied set of tastes of any wine drinker in history.

Driven largely by sales to younger people, Malbec and Moscato were growing impressively in 2011, but sales have largely plateaued. Perhaps the most significant recent gains have been in sales of Pinot Noir and Sauvignon Blanc, which have not only grown comfortably, but established themselves as the varietals of choice for high-dollar drinkers. Merlot and Syrah sales have suffered, with the latter losing half its already small market share in the past five years. But growers can take heart that sales of domestic red blends—often containing Merlot and/or Syrah—continue to grow.

The WMC found that younger wine drinkers clamor for diversity in regions and styles more than ever. When the researchers asked Millennials whether they had bought a wine from certain regions in the past three months, almost every area showed gains compared to a similar survey in 2012. While Australian wine sales continue to suffer, 46 percent of Millennials said they bought a bottle of Aussie wine in the past three months, up from 38 percent in the 2012 survey. Italy was up 10 points to 72 percent and France up 9 percent to 69.

And at least 30 percent of high-frequency wine-drinking Millennials said they had bought wine from Washington, Oregon, Chile, Argentina, Germany, Portugal, South Africa, Greece, Austria, New York, New Zealand or Spain in the past three months—higher than for their Boomer counterparts, often significantly higher. The one major region that did not show growth in the past three years on this question was California. While still the most popular provenance category among wine drinkers, it was the only region Baby Boomers were more likely to buy from than Millennials.

This openness to variety expands to styles as well: Nielsen found that sparkling wine now accounts for 9 percent of off-premise sales, by value. Italian sparklers, driven by Prosecco, have doubled their share of the bubbly market in the past five years. Rosé is "definitely on a tear," said Nielsen SVP Danny Brager. In 2015, fives times more American cash went to premium rosé than in 2011.

While American women have made up a slightly larger share of wine purchasers in recent years, the WMC found that the gender gap widens among Millennials, particularly younger ones. A full two-thirds of high-frequency wine drinkers under 30 years old in 2015 were women. For thirtysomething Millennials, it changes to an even split.

"Celebrate that wine is winning with women," advised Nielsen's Danielle Kosmal, pointing out that Millennial women spend more than their male counterparts. They're also more likely than older women to consider themselves "highly involved" in wine—to self-identify as wine geeks or even collect. But the data makes some worry that the wine industry is not effectively targeting younger men.