The invention relates to recombinant expression of a variant form of a fungal C1 strain β-glucosidase. The invention also relates to the generation of fermentable sugars from biomass and the production of biofuels by fermentation of the sugars using genetically modified organisms expressing the β-glucosidase variant. The invention provides methods for producing a fermentable sugar, such as glucose, from cellobiose by contacting cellobiose with a recombinant β-glucosidase variant protein, such as a variant protein secreted by a recombinant host cell into culture medium. Methods of the invention may be used for conversion of a biomass substrate to a fermentable sugar, and ultimately to ethanol or other biofuel.