Guinness, the Irish stout, gives the brine for these simple barbecued lamb steaks much of its punch. Like most dark beers, Guinness has a bittersweet molasses flavor, which is great with lamb. But the hidden power of a Guinness brine is its alcohol content (about 4 percent). Alcohol accelerates the absorption of flavorful components directly into the protein structure of meat, yielding a steak that not only retains about 10 percent more moisture, but also is able to deliver a hit of seasoning with every bite. The flavors of chipotle chiles and cumin in the brine are reinforced with a smoky rub and a dark, pungent Guinness BBQ sauce. A word of warning: the sauce burns easily, so only brush it on the meat at the very end of grilling. In fact it is more flavorful served as a table sauce, although the steaks do look nice varnished with glaze.