By Harold McGee
Chocolate contains two related alkaloids, theobromine and caffeine, in the ratio of about 10 to 1. Theobromine is a weaker stimulant of the nervous system than caffeine is; its main effect seems to be a diuretic one. (However it is quite toxic to dogs, who can suffer serious poisoning from chocolate candies.) A 1-oz /30 gm piece of unsweetened chocolate contains around 30 mg of caffeine, around a third the dose in a cup of coffee; sweetened and milk chocolates contain substantially less. Cocoa powder has around 20 mg caffeine per tablespoon/10 g.