By Julia Burke, Beer Editor Brooklyn Main Engine Start is the first beer out of the gate of Brooklyn's spanking new brewhouse, and it's a cool lesser-known Belgian style: the Abbey "singel," which is the lightest of the Trappist styles. Traditionally drunk at lunchtime (but then, so am I), singels are a simpler, lower-alcohol alternative to the better-known and more wallop-packing dubbels and tripels. This particular one is only 6% ABV, which is apple juice for most of today's DIPA and quad lovers. Main Engine Start pours a surprisingly clear (according to the brewery it's unfiltered) toasted straw gold color…