A method for making a thermostable polypeptide of interest in a modified Trichoderma host cell which comprises: a modification that substantially reduces or prevents production of a thermostable endoglucananse V by the host cell, an exogenous nucleic acid molecule encoding the thermostable polypeptide of interest operably linked to a promoter whereby at least one endogenous polypeptide and the polypeptide of interest is each expressed in vivo by the Trichoderma host cell, the method comprising: incubating the modified host cell in a medium suitable for the modified host cell to produce the thermostable polypeptide of interest and the endogenous polypeptide, whereby each of the endogenous polypeptide and the thermostable polypeptide of interest is expressed by the modified host cell; and subjecting the thermostable polypeptide of interest and the endogenous polypeptide to an elevated temperature, wherein the elevated temperature is sufficient to substantially inactivate the endogenous polypeptide, but insufficient to inactivate the thermostable polypeptide of interest and EGV if it were present; whereby the thermostable polypeptide of interest is produced in active or functional form substantially in the absence of activity from the endogenous polypeptide. a modification that substantially reduces or prevents production of a thermostable endoglucananse V by the host cell, an exogenous nucleic acid molecule encoding the thermostable polypeptide of interest operably linked to a promoter whereby at least one endogenous polypeptide and the polypeptide of interest is each expressed in vivo by the Trichoderma host cell, the method comprising: incubating the modified host cell in a medium suitable for the modified host cell to produce the thermostable polypeptide of interest and the endogenous polypeptide, whereby each of the endogenous polypeptide and the thermostable polypeptide of interest is expressed by the modified host cell; and subjecting the thermostable polypeptide of interest and the endogenous polypeptide to an elevated temperature, wherein the elevated temperature is sufficient to substantially inactivate the endogenous polypeptide, but insufficient to inactivate the thermostable polypeptide of interest and EGV if it were present; whereby the thermostable polypeptide of interest is produced in active or functional form substantially in the absence of activity from the endogenous polypeptide. incubating the modified host cell in a medium suitable for the modified host cell to produce the thermostable polypeptide of interest and the endogenous polypeptide, whereby each of the endogenous polypeptide and the thermostable polypeptide of interest is expressed by the modified host cell; and subjecting the thermostable polypeptide of interest and the endogenous polypeptide to an elevated temperature, wherein the elevated temperature is sufficient to substantially inactivate the endogenous polypeptide, but insufficient to inactivate the thermostable polypeptide of interest and EGV if it were present; whereby the thermostable polypeptide of interest is produced in active or functional form substantially in the absence of activity from the endogenous polypeptide.