<Tr> <Th> Heat </Th> <Td> Above peak </Td> </Tr> <Tr> <Th> Scoville scale </Th> <Td> 16,000,000 SHU </Td> </Tr> <P> Capsaicin (/ kæpˈseɪ. ɪsɪn / (INN); 8 - methyl - N - vanillyl - 6 - nonenamide) is an active component of chili peppers, which are plants belonging to the genus Capsicum . It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact . Capsaicin and several related compounds are called capsaicinoids and are produced as secondary metabolites by chili peppers, probably as deterrents against certain mammals and fungi . Pure capsaicin is a hydrophobic, colorless, highly pungent, crystalline to waxy compound . </P> <P> The compound was first extracted in impure form in 1816 by Christian Friedrich Bucholz (1770--1818). He called it "capsicin", after the genus Capsicum from which it was extracted . John Clough Thresh (1850--1932), who had isolated capsaicin in almost pure form, gave it the name "capsaicin" in 1876 . Karl Micko isolated capsaicin in its pure form in 1898 . Capsaicin's chemical composition was first determined by E.K. Nelson in 1919, who also partially elucidated capsaicin's chemical structure . Capsaicin was first synthesized in 1930 by Ernst Spath and Stephen F. Darling . In 1961, similar substances were isolated from chili peppers by the Japanese chemists S. Kosuge and Y . Inagaki, who named them capsaicinoids . </P>

Where does the heat in chillies come from