Alkaloids. I can't remember if the heat denatures them or they are solluble, I think it's a mix of both.
There's a theory out there that 'bitter tasters' are an evolutionary adaptation by our Eastern European forebears who lived in an area where alkaloid levels were high in soils. If you avoided alkaloid-embittered foods your liver lasted longer, and so your genes were better represented.
There's a theory out there that 'bitter tasters' are an evolutionary adaptation by our Eastern European forebears who lived in an area where alkaloid levels were high in soils. If you avoided alkaloid-embittered foods your liver lasted longer, and so your genes were better represented.