Therefore, FAN in the fermenting substrate is important for yeast performance and S. cerevisae is only capable of assimilating amino acids. The higher the FAN contents in the fermented slurry, the faster the fermentation process. Yan et al. (2010) made the same conclusion about the effect of FAN on fermentation efficiency of field-sprouted sorghum and wheat. The assimilable nitrogen was found to be related to FAN and the addition of diammonium phosphate (DAP) increased fermentation rate (Blateyron et al., 2008). Thomas and Ingledew (1990) also reported that supple- mentation of wheat mash with an external source of assimilable nitrogen not only resulted in an increased fermentation rate but also yielded a greater amount of ethanol.