The aim of this work was to explore the possibility for development of the new, low-energy demanding process for bioethanol production directly from sugar beet cossettes. For that purpose a two-stage bioreactor system was assembled where the first stage was the vertical packed-bed column in order to use the vertical column in the first stage as an extracting column filled with the packed-bed of sugar beet cossettes that were extracted with concentrated suspension of baker’s yeast thus performing simultaneous extraction and fermentation. The second stage in a bioreactor system was a stirred tank bioreactor. The extraction of sugars was studied in 0,5 and 1,0 [m] column at extractant temperature of 20, 28, 36 and 72°C, respectively, by using two different residence times 24 and 49 [min]. Non-structured mathematical models of sugar extraction process were developed using linear, nonlinear and surface response regression methods as well as by the use of ternary plots. Also, the structured compartment type mathematical model for the sugar extraction from the sugar beet cossettes was established and explored in detail. The commercial baker’s yeast was the working microorganism in the simultaneous process of extraction and fermentation of sugar beet cossettes, thus it was subjected to the thorough fermentation kinetic analysis. Based on achieved results an own formal kinetic mathematical model for microbial conversion of sugars to ethanol (containing substrate and product inhibition terms) was developed and interconnected with the structured mathematical model of extraction (convection/diffusion mass transfer). This combined mathematical model was applied for the modelling of simultaneous extraction and fermentation of sugar beet cossettes in the two step bioreactor system. The model described correctly the new bioprocess and was able to predict values of parameters that have not been able to determine experimentally in those heterogeneous systems. It was proven that the model could be additionaly improved by the use of the computational fluid dynamics calculations.