American researchers say they have determined what gives cannabis its skunky smell. Scientists from Indiana-based Byers Scientific and Iowa State University say the compound 3-methyl-2-butene-1-thiol (“321 MBT”) is the main source of the odor, and not cannabis plant terpenes, which have generally been considered to cause the smell. The research team used analytical chemistry, leaf enclosure study and field observation to isolate and identify the aroma’s source. 321 MBT is the same chemical that causes the skunky-like aroma in spoiled beer, the scientists said. Hops, the main ingredient in beer, is also of the Cannabaceae plant family. The research is part of efforts to devise ways to eliminate the smell.