With the aid of compounds labeled with sulfur-35, the precursors of sunlight-flavor mercaptan were compared. Sodium sulfide was more active than cysteine in serving as the sulfur source of mercaptan. The effectiveness of humulones, acetolupuphenone as well as Carson's isohumulones, and in weaker extent, lupulones as the precursor of carbon moiety of the mercaptan was shown.
