TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: In the method for SSF, the complete fermentation medium comprises an effective amount of the inverting beta -xylosidase such that the complete fermentation medium produces less short chain AXP than does a control fermentation medium lacking the inverting beta -xylosidase. The complete fermentation medium comprises an effective amount of the inverting beta -xylosidase such that the complete fermentation medium produces at least 40-70% less AXP than does a control fermentation medium lacking the inverting beta -xylosidase. The AXP is a methyl- beta - xylopyranoside (MXP), an ethyl- beta -xylopyranoside (EXP), a propyl- beta - xylopyranoside (PXP), or a butyl- beta -xylopyranoside (BXP). The complete fermentation medium comprises an effective amount of the inverting beta -xylosidase to increase the yield of the fermentation product, as compared to the yield of the fermentation product from culturing a control fermentation medium lacking the inverting beta -xylosidase. The yield of the fermentation product is increased by at least 1-10%. The fermentation product is an alcohol, where the alcohol is methanol, ethanol, propanol, propane-1,3-diol, or butanol. The inverting beta -xylosidase is a GH43 family enzyme. The inverting beta -xylosidase is an Fv43D, a Pf43A, an Fv43E, an Fv43B, an Af43A, an Fo43A, a Gz43A, or a XynB3 polypeptide. The Fv43D polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 2, or to residues 21 to 350 of SEQ ID NO: 2. The Pf43A polypeptide has at least 90% sequence identity an amino acid sequence corresponding to SEQ ID NO: 8, or to residues 21 to 445 of SEQ ID NO: 8. The Fv43E polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 10, or to residues 19 to 530 of SEQ ID NO: 10. The Fv43B polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 12, or to residues 17 to 574 of SEQ ID NO: 12. The Af43A polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 14, or to residues 15-558 of SEQ ID NO: 14. The Fo43A polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 24, or to residues 21 -348 of SEQ ID NO: 24. The Gz43A polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 22, or to residues 19-340 of SEQ ID NO: 22. The XynB3 polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 25. The inverting beta -xylosidase is present in the complete fermentation medium at a concentration of 0.3-10 mg/g xylan in the xylan-containing biomass. The inverting beta -xylosidase is present at a concentration of 0.4-10 mg/g xylan in the xylan-containing biomass, preferably 0.3-3 mg/g xylan in the xylan-containing biomass. The method is performed as a continuous, a batch, or a fed-batch SSF process. The method further comprises forming the complete fermentation medium. Forming the complete fermentation medium comprises combining (a) the fermenting microorganism , (b) the xylan-containing biomass, (c) the cellulase, (d) the hemicellulase, (e) the inverting beta - xylosidase, and (f) a medium lacking one or more or all of (a)-(e). The cellulase is present in the form of a whole cellulase preparation. The whole cellulase preparation comprises a hemicellulase. The whole cellulase preparation is a culture broth obtained from culturing a filamentous fungus, where the filamentous fungus is a T. reesei. The T. reesei has been engineered such that the native beta -xylosidase gene has been deleted or inactivated. The fermenting microorganism is a fungus, where the fungus is a Saccharomyces cerevisiae yeast. The fermenting microorganism is a bacterium, where the bacterium is a Zymomonas mobilis. The xylan-containing biomass is corn stover, bagasses, sorghum, giant reed, elephant grass, Miscanthus, Japanese cedar, wheat straw, switchgrass, hardwood pulp, or softwood pulp. The xylan-containing biomass is in a slurry. The xylan-containing biomass has been pretreated. The method further comprises recovering the fermentation product. The complete fermentation medium comprises a greater amount of inverting beta -xylosidases than that of retaining beta -xylosidases on a mole basis, molecular weight basis, or on both a mole basis and a molecular weight basis. The ratio of inverting beta -xylosidases to retaining beta -xylosidases in the complete fermentation medium is at least 2:1, on a mole basis, molecular weight basis, or on both a mole basis and molecular weight basis. The complete fermentation medium comprises an effective amount of retaining beta -xylosidase such that the complete fermentation medium produces more AXP than does a control fermentation medium lacking the retaining beta -xylosidase or having a lower amount of the retaining beta -xylosidase. The retaining beta -xylosidase is a GH3, GH30, GH31 , GH39, GH52, GH54, or GH116 family enzyme. The retaining beta -xylosidase is a XlnD, an Fv30A, an Fv30B, an Fv39A, an Fv39B, or a XynB polypeptide. The XlnD polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 40, or to residues 18-804 of SEQ ID NO: 40. The Fv30A polypeptide has at least 90% sequence identity an amino acid sequence corresponding to SEQ ID NO: 42, or to residues 20-537 of SEQ ID NO: 42. The Fv30B polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 44, or to residues 25-485 of SEQ ID NO: 44. The Fv39A polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 46, or to residues 20-439 of SEQ ID NO: 46. The Fv39B polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 48, or to residues 19-456 of SEQ ID NO: 48. The XynB polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 50. The XylA polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 52 or to residues 19-705 of SEQ ID NO: 52. The Xyl1 polypeptide has at least 90% sequence identity to an amino acid sequence corresponding to SEQ ID NO: 54. Sequences not defined here may be found at ftp://ftp.wipo.int/pub/published_pct_sequences/publication. The method further comprises forming the complete fermentation medium, where the step of forming the complete fermentation medium comprises combining (a) the fermenting microorganism, (b) the xylan-containing biomass, (c) the cellulase, (d) the hemicellulase, (e) the retaining beta -xylosidase, and (f) a medium lacking one or more or all of (a)-(e). The cellulase is present in the form of a whole cellulase preparation. The whole cellulase preparation comprises a hemicellulase. The whole cellulase preparation is a culture broth obtained from culturing a filamentous fungus. The filamentous fungus is a T. reesei, where the T. reesei has been engineered to overexpress a native retaining beta -xylosidase gene or to express a foreign retaining beta -xylosidase gene. The fermenting microorganism is a fungus or a bacterium. The xylan-containing biomass has been pretreated. The method further comprises recovering the AXP compound. The complete fermentation medium comprises a greater amount of retaining beta -xylosidases than inverting beta -xylosidases on a mole basis, molecular weight basis, or on both a mole basis and a molecular weight basis. The method for producing a cellulase preparation further comprises recovering the cellulase preparation. In the method of producing a fermentation product, the fermentation product is an alcohol, where the alcohol is methanol, ethanol, propanol, propane-1,3-diol, or butanol. Preferred T. reesei Cell: The T. reesei cell is engineered to recombinantly express a GH43 family enzyme. The T. reesei cell is engineered to recombinantly express an Fv43D, a Pf43A, an Fv43E, an Fv43B, an Af43A, an Fo43A, a Gz43A, or a XynB3 polypeptide. The T. reesei cell is engineered to recombinantly express a GH3, GH30, GH31, GH39, GH52, GH54, or GH116 family enzyme. The T. reesei cell is engineered to recombinantly express a XInD, an Fv30A, an Fv30B, an Fv39A, an Fv39B, a XynB, a XylA, or a Xyl1 polypeptide. EXAMPLE - No suitable example given.