When I reviewed the La Cabra brewpub this year, co-owner and brew master Dan Popernack told me I'd tasted only "phase one" of his brewing program. The second phase — an array of various wild yeast ales based on the sour brews with which Popernack made a cult reputation as a home brewer — were still biding their time, maturing in barrels in La Cabra's Berwyn cellar. Well, some of those sour and funky creatures have finally started to appear, and they are worth the wait. Known as the Aleatory Series, which refers to the experiment of melding a careful brewer's deliberate art with the chance element of wild yeast, these monthly small-batch special issues are intended to show Popernack's range and passion for the diverse Belgian art of earthy barrel-aged brews that, like wine, can evolve, sometimes unpredictably, but often sublimely, over longer periods. His first batch this spring (Aleatory No. 1) was an impressive take on a lambic —  dry, crisp, and saison spicy with oak and blushing vivid red from 500 pounds of raspberry. For Aleatory No. 2, set to debut for presale online on Monday, with pick-up at the brewery a week later, Popernack tried his hand at a darker style he's calling "Brun Nouveau," a lighter, four-month-old take on Flanders Oud Bruin, which usually ages a year or more. La Cabra's Nouveau hit all the trademark sweet-and-sour balsamic notes of a typical Oude, but with less brooding depth and complexity, and a rambunctious fizz that reminded me vaguely of chinotto soda. If it's possible for such a beer to be a summer brew, this is it. Popernack created the online preorder system because he despises lines that so often accompany anticipated beer releases. But a visit to the brewery is still required on June 12. And to make sure the local faithful also get their dibs, a quarter of this 70-case batch has already been set aside at the brewery for walk-in purchase. If all goes well, the Aleatories will become a monthly event worth the trip to Berwyn.

La Cabra Brewing Co.'s Aleatory Series No. 2, $18. Preorders available Monday online at lacabrabrewing.com with pick-up required June 12 at the brewery, 642 Lancaster Ave., Berwyn, 610-240-7908.