There is no hard-and-fast definition for “nano-brewery,” but if you set 1,000 barrels a year as the upper limit, you probably won’t have to fear contradiction. The National Geographic Society used this definition in gathering beers for its annual tasting, held May 17 at its 17th Street NW headquarters, dubbed “Mini-Micros: A World Tour of Small Breweries.”

These teeny-tiny beermakers tend to distribute locally...very locally. “Most beer never gets farther than 20 miles from the brewery,” noted host Garrett Oliver, brewmaster for Brooklyn Brewery. But the society, with the help of some specialty importers and Dave Alexander of R.F.D. Washington (who cosponsored the event), managed to corral nine beers from seven countries.

“Six of these beers came through this morning,” noted Rock Wheeler, editorial manager for National Geographic Live. Some arrived in slightly shook-up condition. “You can almost shave with this,” commented Oliver of one super-foamer.

My award for find of the evening goes to Guineu Riner from Ca l’Arenys in Barcelona, Spain, which is imported into the United States by Shelton Brothers of Belchertown, Mass. This brisk, hoppy, straw-colored ale with a fresh citrusy aroma measures only 2.5 percent alcohol by volume. Yet you don’t feel deprived in the least — it tastes full-strength. Oliver suggested that saisons — Belgian farmhouse ales — might have resembled this beer back in the day when they were “a replacement for water” for thirsty farm workers. At my table, where we shared three 11-ounce bottles among six people, we wondered aloud whether you could get a buzz even if you downed the entire North American allotment.

The beer with the most unusual ingredient was Saison Cazeau from the Brasserie de Cazeau in Templeuve, Belgium, which incorporates elderflowers from a tree in the brewer’s backyard. Brought to America by 12 Percent Imports in Brooklyn, the golden ale had a floral aroma and a biscuity malt sweetness with a crisp finish.

The beer that traveled the farthest was Renaissance MPA from Renaissance Brewing Co. in Marlborough, New Zealand. This kiwi take on the double IPA style (it clocks in at 8.5 percent alcohol by volume) makes abundant use of Rakau hops, a New Zealand strain with a perfumy, bitter bite. The Web site claims there are “approximately 120 hops” per 16.9-ounce bottle. This is not an unbalanced beer, however; it’s got a huge reservoir of caramel malt to keep the bitterness in check.

The MPA was contrasted with Kern River Just Outstanding IPA. The lone American beer of the evening had been Fed-Exed to Washington from this Kernville, Calif. microbrewery/brewpub. Even Oliver admitted he hadn’t tasted this beer until that evening. Less potent (6.7 percent alcohol) than the kiwi brew, it was more aggressively flavored, a runaway hop train with the characteristic grapefruit and pine sap flavors of Simcoe and Amarillo hops.

The most complex beer was the final offering, Cuvee Alex Le Rouge from the Brasserie Des Franches-Montagnes in Saignelegier, Switzerland. This imperial stout, an opaque ebony color with a tan head, is flavored with black pepper, vanilla and tea, according to the Web site for B. United International, the beer’s importer. The tea seemed missing in action, but the pepper blended with the dark malts to produce an almost parsley-like spiciness, and the vanilla smoothed out the rough edges. At 10.28 percent alcohol, it was also our strongest beer of the evening.

Cuvee Alex had a refreshing tartness, and it inspired Oliver to muse whether the National Geographic Society should devote a future tasting entirely to sour beers. Today, we tend to associate sour with spoilage. But “stale beer” was once considered a desirable product in England, and the Germans too brewed a tart refresher called Berliner weisse — a pale, low-alcohol wheat ale fermented with the assistance of lactobacillus.

We got to sample a revivalist version of this style: 1809 Berliner Weisse, created by Dr. Fritz Briem of Germany’s prestigious brewing academy, the Doemens Institute. The name comes from the year that Napoleon allegedly sampled this spritzy brew and pronounced it the “champagne of the north.”

The few modern versions that still exist in Germany are often dosed with raspberry syrup to make them more palatable to a general audience. But the 1809 (also a B. United import) held up well on its own with its tart, fruity and slightly earthy flavor profile.

Before mass-market golden lagers dominated the world, about 200-250 cafe-breweries in Berlin produced this style, noted Oliver. “There was a day when even the Germans used to be funky.”