What to Know Before You Order the New 'Flat White' at Starbucks

— -- The flat white is coming. Flat what?

Starting in stores nationwide on Tuesday after tests in limited markets and abroad, Starbucks is introducing a new drink to its menu that you've probably never heard of. The flat white is a drink not easily defined and much discussed within the coffee community, but it boils down to this: a five- to six-ounce beverage with a double shot of espresso with lightly aerated milk that has the appearance of velvet or paint rather than foam, according to Toby’s Estate Coffee’s head of education Allie Caran.

“It’s one of the most confusing drinks,” Caran told ABC News. “There are many different definitions, but the best way to look at flat white is a little more within its cultural context.”

Even its cultural context, though, is murky. Its birth in the 1990s is widely credited to Australia, though New Zealand also claims ownership. As the popular story goes, a cappuccino 20 years ago in that area would have a “very dry foam, which means they’ve added a ton of air, almost like a meringue-top foam,” Caran said.

The resulting beverage was very dry on top, and coffee drinkers were requesting a smoother-textured “flat milk drink,” and thus was born the flat white. So, it generally all boils down to the topping, with the flat white’s being much smoother, wetter and thinner than a cappuccino’s.

“It merges your milk and espresso together, whereas in the Australian cappuccino, you’ll find the espresso at the bottom and foam at the top,” Caran explained. “A flat white is a little more integrated.”

According to a Starbucks spokesperson, its flat white “is made with two ristretto shots, topped with a thin layer of velvety steamed whole milk and finished with a latte art dot. Starbucks baristas perfectly steam milk into creamy micro-foam and carefully free pour to allow the espresso to rise to the top of the beverage for a bold coffee flavor with a sweeter finish.”

A ristretto shot, to add to the drink’s confusion, is a short espresso shot made with the same amount of coffee grounds but half the water for a more concentrated flavor.

“I commend Starbucks, because it’s an ambitious drink to do consistently well,” Caran said. “It requires a pretty good amount of attention on the barista’s part when it comes to texturing that milk properly. You want just the tiniest bit of aeration, but you don’t necessarily want to make a foamy milk. To make something that’s really pourable and not scalded does require a certain amount of constant vigilance.”

You can see if they succeed starting Tuesday.