NOVELTY - Preparing fermentation product involves, pretreating biomass material with a solution containing at least one alpha -hydroxysulfonic acid to produce a pretreated biomass mixture containing at least one fermentable sugar, adding saccharification enzymes to pretreated biomass mixture, performing enzymatic hydrolysis of cellulose by the one or more saccharification enzymes to generate a hydrolyzate, and adding at least one fermentation microorganism to the hydrolyzate under a suitable condition for simultaneous saccharification and fermentation.    USE - The method is useful for preparing fermentation product (claimed).    ADVANTAGE - The method is cost-effective, and produces high yield of fermentation product.    DETAILED DESCRIPTION - Preparing fermentation product involves (a) providing a biomass material, pretreating the biomass material by contacting the biomass material with a solution containing at least one alpha -hydroxysulfonic acid to produce a pretreated biomass mixture containing at least one fermentable sugar, adding one or more saccharification enzymes to the pretreated biomass mixture, where the pretreated biomass mixture has a suitable condition for the one or more saccharification enzymes, performing enzymatic hydrolysis of cellulose by the one or more saccharification enzymes for greater than 24 hours to generate a hydrolyzate, and adding at least one fermentation microorganism to the hydrolyzate under a suitable condition for simultaneous saccharification and fermentation to generate a fermentation product, or (b) providing a pretreated biomass mixture comprising at most 0.5 wt.% component chosen from hydroxyl-methyl-furfural, furfural, and its combination, adding one or more saccharification enzymes to the pretreated biomass mixture, where the pretreated biomass mixture has a suitable condition for the one or more saccharification enzymes, performing enzymatic hydrolysis of cellulose by the one or more saccharification enzymes for greater than 24 hours to generate a hydrolyzate, and adding at least one fermentation microorganism to the hydrolyzate under a suitable condition for simultaneous saccharification and fermentation to produce a fermentation product.