Fourteen malodorous compds. (mostly hydrocarbons) were identified in off-gases from yeast production by gas chromatog. coupled to mass spectrometry. Three of the compds. were subjected to degrdn. with O(3) sep. or in the mixt. The efficiency of sep. degrdn. was 74.2-96.1%. Degrdn. degree of 1-hydroxmethyl-2,5-ditertbutylbenzene (ref. compd.) and of resp. mixt. was lower.