With "craft" beers exploding like double bock in a paint shaker, savvy bars are tempting beer snobs with smaller-than-small-production suds. Tory Row and Green Street Grill, for example, offer Gritty McDuff’s Black Fly Stout, a Maine beer that taps out at just 70 to 80 barrels annually. Even more exclusive is Pretty Things’ Jack D’Or, poured at Craigie on Main and Deep Ellum: The Cambridge-based brewer constantly tinkers with this farmhouse-style ale, so once a particular batch is gone, it’s gone. D.G.