lawnmower beer
n.— «Summer may be the best time to eschew the exotic and just go for a simple “lawnmower beer”—something to chug after a sweaty session of yard work (Delaware’s Dogfish Head Craft Brewery makes a draft-only “Lawnmower Light”).» —“Wheat beer: A light brew for warmer days” by Bob Batz Jr. Pittsburgh Post-Gazette (Pennsylvania) May 18, 2006. (source: Double-Tongued Dictionary)
Beer expert Michael Jackson used the term “lawnmower beer” in 1989 when addressing a crowd of beer enthusiasts in Whistler, BC. He meant it in a negative sense, ie. beer that had no taste but quenched one’s thirst.