NOVELTY - An isolated thermostable enzyme that is capable of hydrolyzing glycosidic bond of steryl glycosides or acylated steryl glycosides is new.    USE - As isolated thermostable enzyme capable of hydrolyzing glycosidic bond of steryl glycosides or acylated steryl glycosides for reducing steryl glycoside in a sample (where the sample comprises oil, fat, or bio fuel (preferably biodiesel)).    ADVANTAGE - The thermostable enzyme capable of hydrolyzing the glycosidic bond of a steryl glycoside (preferably steryl glucoside) or acylated steryl glycoside (preferably acylated steryl glucoside) reduces amount of steryl glycoside by at least 20% (preferably at least 80%) in a biodiesel. The processed sample comprises less than 20 parts per million (ppm) of steryl glycoside. The enzyme has a hydrolytic activity of at least 5 g of steryl glycoside per gram of enzyme per hour at 50-99 degrees C. The method produces biodiesel fuel with high quality, which is more cost-effective and competitive in the global market. The improved enzymes can significantly reduce current production costs and provide premium high-quality biodiesel by eliminating major impurities in an environmental-friendly and commercially competitive way. The enzymes eliminate key impurities in plant-based biodiesel, such as steryl glycosides and saturated monoacylglycerols (SMGs) which result in the formation of insoluble materials that compromise quality and performance of the end product. The method allows inexpensive production of enzymes and using such enzymes to remove steryl glycosides from biodiesel, biodiesel precursors, or biodiesel derivatives. The biodiesel obtained has better quality, when compared with a comparable control biodiesel in which steryl glycosides have not been removed.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) reducing (M1) steryl glycoside in a sample involving mixing thermostable enzyme with a sample comprising steryl glycoside under condition suitable for thermostable enzyme for a period of time to degrade steryl glycoside, thus reducing steryl glycoside in the sample to obtain a processed sample;    (2) an oil produced by the method (M1);    (3) generating (M2) a gene encoding a variant steryl glucosidase involving a) growing in a cultural medium several host cells transformed with a first library of variant steryl glycosidase genes, where expression of each variant steryl glycosidase genes is under control of a promoter that linearly responds to concentrations of an inducer added to culture medium, where host cells require a sterol to grow and are unable to synthesize ergosterol, and the cultural medium comprises steryl glycosides and a first concentration of inducer so as to permit only a host cell expressing a variant steryl glycosidase with sufficient activity to form a colony, and b) recovering the variant steryl glycosidase gene from colony;    (4) producing a recombinant steryl glucosidase involving expressing the codon optimized sequences in a suitable heterologous host cell to generate recombinant steryl glucosidase, and isolating the recombinant steryl glucosidase; and    (5) a host cell expressing a gene produced by the method (M2).