TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preparation (claimed): Preparing the modified mannanase comprises culturing the host cell and isolating the modified mannanase from the culture. Preferred Mannanase: The modified mannanase has a substitution at one or more of the positions 4, 7, 11, 13, 31, 41, 66, 70, 74, 97, 101, 113, 132, 146, 148, 170, 173, 181, 182, 185, 186, 187, 189, 201, 207, 215, 216, 220, 252, 255, 259, 274, 280, 281, 282, 313, 316, 317, 325, 331, 341, 345, 351, or 352 relative to the numbering of wild-type mannanase given in SEQ ID NO. 1. In the modified mannanase, (i) the insertion, deletion and/or substitution is located in the second half of the molecule, preferably the changes occur at a position of 200 or higher according to the numbering of wild-type mannanase; and/or (ii) the number of insertions, deletions, and substitutions is 1-30, preferably 1-5. The substitution relative to the numbering of wild-type mannanase is one or more of the substitutions given in the specification. The substitution relative to the numbering of wild-type mannanase is selected from: (i) the amino acid N173 is substituted by Ala, Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Pro, Gln, Arg, Ser, Thr, Val, Trp, or Tyr, preferably N173 is substituted by H; (ii) the amino acid V181 is substituted by Ala, Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Pro, Gln, Arg, Ser, Thr, Trp, or Tyr, preferably V181 is substituted by Ala; (iii) the amino acid V148 is substituted by Ala, Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Pro, Gln, Arg, Ser, Thr, Trp, or Tyr, preferably V148 is substituted by Ile; (iv) the amino acid V187 is substituted by Ala, Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Pro, Gln, Arg, Ser, Thr, Trp, or Tyr, preferably V187 is substituted by Met; (v) the amino acid T201 is substituted by Ala, Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Pro, Gln, Arg, Ser, Thr, Val, Trp, or Tyr, preferably T201 is substituted by Ser; (vi) the amino acid L207 is substituted by Ala, Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Pro, Gln, Arg, Ser, Thr, Val, Trp, or Tyr, preferably L207 is substituted by Phe; (vii) the amino acid A215 is substituted by Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Pro, Gln, Arg, Ser, Thr, Val, Trp, or Tyr, preferably A215 is substituted by Thr; (viii) the amino acid Y220 is substituted by Ala, Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Pro, Gln, Arg, Ser, Thr, Val, or Trp, preferably Y220 is substituted by Phe; (ix) the amino acid F274 is substituted by Ala, Cys, Gly, His, Ile, Leu, Met, Val, or Trp, preferably F274 is substituted Leu; (x) the amino acid Q280 is substituted by Ala, Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Pro, Arg, Ser, Thr, Val, Trp, or Tyr, preferably Q280 is substituted Arg; (xi) the amino acid N282 is substituted by Ala, Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Pro, Gln, Arg, Ser, Thr, Val, Trp, or Tyr, preferably N282 is substituted Asp; and/or (xii) the amino acid N331 is substituted by Ala, Cys, Asp, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Pro, Gln, Arg, Ser, Thr, Val, Trp, or Tyr, preferably N331 is substituted by Ser. The modified mannanase is derived from mannanase having SEQ ID NO. 1 by introducing two or more of the substitutions selected from F4Y, I7V, Q11R, Q11H, N13D, F31Y, T41I, S66P, I70V, K74M, Q97R, Q101R, N113Y, T132S, K146Q, V148I, P170L, N173H, N173T, V181A, V181H, VISIT, Q182R, T185K, S186N, V187M, V187L, Q189H, T201S, T201A, T201G, L207F, L207W, L207R, L207S, L207Y, A215T, Y216H, Y220F, T252I, N255I, Q259R, F274L, F274M, Q280R, Q280S, Q280L, Q281H, N282D, A313T, A316T, Q317H, V325I, D341E, G345C, P351L, P352L, or N331S in any combination, preferably the modified mannanase comprises one or more of the following combinations of substitutions: F274L/A215T, F274L/N282D, F274L/A215T/N282D, F274L/Y220F, F274L/V187M, F274L/V181A, F274L/V148I, F274L/N173H, F274L/N331S, F274L/N173H/N331S, F274L/L207F, F274L/T201S, F274L/Q280R, T132S/N173T, Q11H/P170L, F31Y/D341E, N173H/G345C, N13D/F274L, F274L/Q280L, F274L/Q317H, S66P/T201S, L207F/F274M, S66P/V181A/V187L, V181A/T252I/N255I, F4Y/I70V/F274L, Q101R/F274L/Q281H, T201G/L207F/F274L, T201S/L207F/F274L, V181T/L207W/A215T/F274L, Q11R/Q189H/T210A/P351L, K74M/F274L/A313T/V325I, N173H/V181H/L207W/F274L, T201S/L207Y/F274L/Q280R, T201S/L207W/F274L/Q280R, T201S/L207R/F274L/Q280R, V181T/L207W/F274M/N331S/P352L, N173H/L207W/A215T/F274L/Q280R, V181H/L207W/A215T/F274L/N282D, N173H/V181T/T201S/L207W/F274L, N173H/V181H/L207W/A215T/F274L, V181H/L207W/A215T/F274L/Q280R/N282D, S66P/N173H/V181H/A215T/F274L/Q280S/N282D, N173H/V181T/L207W/A215T/F274L/Q280R/N282D, or F274L/T201S/Q280R, or a combination of the particular combinations above, most preferably the modified mannanase has the sequence given in SEQ ID NO. 10 (variant B), SEQ ID NO. 11 (variant C), SEQ ID NO. 12 (variant 31), or SEQ ID NO. 13 (variant 16). The modified mannanase is derived from mannanase having SEQ ID NO. 1 by introducing one or more of the substitutions given in the specification, where the mannanase has, relative to the wild-type mannanase, increased thermostability, and increased stability towards low pH values and/or protease enzymes. EXAMPLE - No suitable example given.