Yeast growth is affected not only by the operative conditions (temperature, pH, sugar concentration) but also by the intrinsic properties of the investigated system, namely, type of strain, culture medium, and physiological state of the inoculum. Several authors describe the influence of the operative conditions quantitatively, whereas the effects of the intrinsic properties are in general reported as qualitative observations. In order to investigate these aspects, which are very important in the optimization of industrial baker's yeast production, several yeast growth runs were carried out varying the type of strain, the culture medium, and the physiological state of the inoculum employed. Experimental data on both batch and fed-batch baker's yeast growth were interpreted quantitatively using a modified and improved suitable cybernetic model. The results of a sensitivity analysis performed on the kinetic parameters of the model have shown that parameters related to the different culture medium and strain can be obtained by mathematical regression on experimental data. The parameters relating to the different physiological state of the inoculum are independent from strain and culture medium employed, so that one batch and one fed-batch growth run, carried out in defined operative conditions, are sufficient to determine the whole set of model parameters. Moreover, the improved model has been tested by simulating fed-batch growth runs, performed under different operative conditions, demonstrating its predictive power.