The fermentation process of wheat dough was studied by laser-based trace gas detection. A CO-laser-driven photoacoustic spectrometer was used to monitor simultaneously, in real time, the ethanol and acetaldehyde production rates of two commercial types of active dry yeast ( Saccharomyces cerevisiae) in wheat dough substrates. Both types of yeast, Oand B, produced ethanol for 5 hours. Acetaldehyde was yielded only during 100 minutes by the yeast O, whereas the yeast Bgenerated this compound for 3.5 hours. The total ethanol and acetaldehyde productions amounted to 1.50 mL/g dough and 4.5 µ L/g dough in the Ocase, and 0.84 mL/g dough and 14.75 µ L/g dough, in the Bcase, respectively. The yeasts were also tested for their ability tometabolize mixes consisting of the control wheat dough substrate and extra amounts of glucose or maltose. Both types of yeasts showed a similar ability to consume the added glucose, however, only the yeast Bwas found to possess an adapted enzymatic system to metabolize maltose. This work showed the efficiency of applying photoacoustic trace gas detection to food technology research for on-line monitoring of fermenting wheat dough.