It used to be that everything we knew about Irish beverages could be explained over an intimidatingly dark beer with a half-inch head, or a quick dram of whiskey (shot, not sipped) poured from a green-tinted bottle.

Whether or not we drank Guinness and Jameson on the regular, they've always been Americans' cultural Kool-Aid for celebrating occasions as raucous as St. Patrick's Day, a holiday that we know as little about as we do, well, Irish whiskey.

Now's a good time to dig deeper. With all four of Ireland's major distilleries owned by spirits conglomerates (Pernod Ricard and Diageo have one each; Beam Inc. recently bought its second), we're reaping the harvest of a centuries-old spirit fueled by 21st century distribution, says Patrick Caulfield, U.S. regional manager with Irish Distillers, Pernod Ricard.

"The leading spirits companies have recognized (Irish whiskey as a growing category) and have acquired Irish whiskey brands over the last few years to take advantage of this opportunity," Caulfield says. "This means that all Irish whiskies in the U.S. are now backed by big spirits companies with the resources to market these brands, and also insure that supply can keep up with demand."

The proof is in the numbers: Irish whiskey is the fastest-growing category in the American whiskey market, up 400 percent since 2002, and up nearly 23 percent in the past year, according to the Distilled Spirits Council of the United States.

Best-selling Jameson is in part contributing to the rapidly growing category with select reserves like Jameson Black Barrel, introduced last year. But there are more than a dozen other brands widely imported to the States, ranging from affordable blends and premium single-malts to the unique single pot-still category, which has the potential to follow small-batch bourbon's popularity among whiskey geeks.

Of course, the first step is converting shot-drinkers to whiskey connoisseurs, says John Ryan, who represents the seventh generation behind Powers, one of the brands riding Jameson's coattails.

Once the palette matures, Ryan says, it becomes more sophisticated, as does the drinker. "We are really quite confident that we can educate (drinkers) as their taste matures," Ryan says.

For Bob Gorman, director of marketing world whiskies at Beam, that education means steering novices toward far reaches of their portfolio. "We think there's tremendous opportunity for the whole category," he says, "so we can bring other whiskey drinkers back to Irish whiskey, where they belong."

Irish whiskey, defined

For a spirit to be deemed Irish whiskey, it must meet a handful of requirements defined by the Irish Whiskey Act of 1980:

• Distilled and aged in Ireland (or Northern Ireland)

• Derived from a yeast-fermented mash of cereal grains (barley is key) resulting in an aroma and flavor reminiscent of those grains, then distilled to an alcohol level less than 94.8 percent

• Aged at least 3 years in wooden casks

• If a spirit contains two or more distillates, it must be labeled as "blended"

Blended

Two or more different malted-barley whiskies blended together, often combining milder column-still whiskey with more intense pot-still whiskey.

Bushmills, $20

Smell: Hints of cinnamon, honey

Taste: Smooth and round, slightly spicy finish

Concannon, $18

Smell: Subtle and nice, not overpowering

Taste: Complex and smooth; hints of smoke from the charred bourbon casks in which it's finished

Jameson Gold Reserve, $22

Smell: Mildly hot, a little sweet

Taste: Familiar, smooth, a bit leathery with a hot aftertaste

Jameson Select Reserve Black Barrel, $35

Smell: Soft anise, softly sweet

Taste: Jameson's smoother, slightly smokier sister; a bit more sipable

Kilbeggan, $20

Smell: Spicy with a touch of hotness, but not too

Taste: Rugged and interesting, chewy and a bit dirty; a working-class whiskey

Michael Collins Blend, $24

Smell: Faint, not too hot

Taste: Fairly sweet but masculine, quite smooth, residual pipe-tobacco flavor

Powers Gold Label, $27

Smell: Quite light, deep nose, rich barley

Taste: Heavy barley overtones, honey-sweet at end

Single malt

A single malted-barley whiskey distilled in a pot still.

Connemara Peated Single Malt, $45

Smell: Scotch-like, because of the peat; heavy smoke and familiar sweet barley smell

Taste: Exactly like Irish whiskey…as if it were raised in Islay, Scotland

Michael Collins 10 Year Old Single Malt, $39

Smell: Richer than the blended version; aging is prevalent

Taste: Round, sweet and rich with a buttery finish

The Tyrconnell Single Malt, $35

Smell: Rich, caramel, a wee bit hot

Taste: Smooth, honey-forward, smoke in back

Single pot still

A single whiskey made from both malted barley and unmalted barley, distilled in a pot still.

Powers John's Lane Release 12-year Single Pot Still, $65

Smell: Sweet, a bit hot

Taste: Smooth and dessert-y; sweet, then peppery with a smoky ending

Redbreast 12, $60

Smell: Spice notes reminiscent of winter

Taste: Deliciously complex, chewy, both tobacco and dried fruit notes at end

Redbreast 15, $70 [adjusted from BevMo to match Binny's scale]

Smell: Simlar to Redbreast 12, but a bit sweeter

Taste: Complex, sophisticated, creamy with lots of body

Single grain

A single whiskey made from just one grain, as opposed to a blend of grains, distilled.

Greenore Single Grain 8-year, $50

Smell: Different, campfire-like, like a heavily smoky bourbon

Taste: Very bourbon-like, not at all like other Irish whiskies