Abstract: A portable olefin gas generating apparatus such as for generating ethylene to initiate the ripening of various climateric fruits. A reaction liquid is fed by gravity to a reaction chamber where it is catalytically converted into the desired olefin gas.The reaction liquid includes an alcohol such as ethanol, a denaturing agent such as a ketone, an ester of a monocarboxylic acid, gasoline or gum rubber and a catalyst activating agent such as an ester of monocarboxylic acid, a straight chain hydrocarbon or an aromatic hydrocarbon.To control the temperature of the gas generator apparatus an electronic temperature controller circuit is used in the reaction chamber.