I have been searching (albeit not very intently) for “Bierkraft” in Park Slope for about two and a half years. Well, it’s where it apparently has been the whole time: at the corner of 5th and Union. It’s a nice little shop that’s devoted 50-50 to beer and food (cheeses, meats, chocolates, cookies, etc). At the back of the store they have a selection of beers on tap, which they will kindly put into a growler in exchange for a large number of American greenbacks. It took quite a while to get my Kelso Pilsner (which, they neglected to tell me, is from Brooklyn), partly because they pressurize the growler to 18psi before filling it. With this system the beer is transferred from keg to bottle without “being poured” so it doesn’t lose any of its carbonation. Sounds hokey, but it tastes good.