The changes in the Helmholtz resonant frequency and acoustic absorption during the rise of bread dough were investigated. The dough volume predicted by using the Helmholtz resonant frequency increased in the fermentation process; however, it was below the true volume. The apparent acoustic absorption coefficients determined by sound intensities increased when the bread dough rose. The acoustic absorption caused by the pores in the dough might decrease the resonant frequency. The increase in the dough volume should change the shape of a part of the power spectrum curve besides the spectrum peak. In order to detect such a small change, the difference spectrum between two spectra obtained at intervals of 1365.34 ms was used. The values predicted based on the frequency of the zero crossover point, such as the isosbestic point, agreed with the dough volume.