Ethanol produced from lignocellulosic biomass has the potential to become a promising alternative to gasoline. In this work the simultaneous saccharification and fermentation (SSF) technology was applied for ethanol production from hardwood with focus on cell growth, ethanol production and contamination. The SSF was performed at PH 5.5 and 35°C for different suspended solid concentrations (8%, 10% and 12%) of pretreated birch slurry which contained 16 % total suspended solids. Two different hexose fermenting yeast strain (Ethanol Red) and pentose fermenting yeast strain were used. Quantifying the concentration of chemical components and metabolites in the fermentation medium demonstrated that glucose and xylose are the major fermentable sugars in the slurry. The higher load of slurry (12%) represents a higher content of carbohydrates and potentially higher end concentration of ethanol. Moreover, more lactic acid is produced with the lower load of slurry (8 % or 10 %), presumably due to a result of a less inhibitory environment for bacterial growth. In this context, acetic acid sticks out as the most important inhibitor with concentrations of 15.2 and 12.5 and 9.7 g/l respectively in the 12 %, 10 % and 8 % (of suspended solids) trials. Using pentose fermenting yeast may lead to higher ethanol production, lower xylose uptake and lower lactic acid formation. Cell viability and cell vitality determination from fermentation media in all the trails represented a sharply decreasing trend during the fermentation for both Ethanol Red yeast strain and the pentose fermenting strain yeast strain apparently due to cell decomposition.