Intensive development of the transport sector and a rise in the prices of fossil fuels boost the demand for fuels from alternative sources of energy, including biofuels. New energy-efficient technologies of fuel production from renewable resources are developed. The aim of the present study was to examine the factors influencing the effectiveness of the process of simultaneous saccharification and fermentation of corn flour with full stillage recycling. The effect of structural changes of starch granules during the long-term repeated SSF process as well as the scale of the process were investigated. Commercially available STARGEN 001 enzymatic preparation and Saccharomyces cerevisiae strain Red Star Ethanol Red were used in the experiment. The results proved that raw material quality is of the utmost importance for the effectiveness of this processes. Bacterial contamination of the raw material caused decreased ethanol productivity despite similar substrate utilization. Process scale turned out to be a second significant factor influencing the SSF outcome. Increase of bioreactor volume resulted in decreased productivity. Repeated stillage recycling and the resulting concentration of broth ingredients has a lesser impact on the process. Ethanol content and the amount of residual starch was independent of the number of operation cycles. Formation of porous granules is predominant as starch undergoes hydrolysis. The affinity of the amylolytic enzyme used towards crystalline and amorphous regions is equal. (C) 2013 Elsevier Ltd. All rights reserved.