By Harold McGee
In general, grass or forage feeding results in stronger-tasting meat than grain or concentrate feeding, thanks to the plants’ high content of various odorous substances, reactive polyunsaturated fatty acids, and chlorophyll, which rumen microbes convert into chemicals called terpenes, relatives of the aroma compounds in many herbs and spices. Another important contributor to grass-fed flavor is skatole, which on its own smells like manure! The deep “beefy” flavor of beef, however, is more prominent in grain-fed animals. And the flavor carried in fat gets stronger as animals get older, as more of the flavor compounds are put into storage. This is why lamb is generally more popular than mutton from mature sheep.