Abstract: Novel hybrid thermostable (1,3-1,4)-.beta.-glucanases, their use in food manufacturing and feed manufacturing, DNA fragments encoding such glucanases, organisms expressing the DNA fragments and a method for producing the thermostable (1,3-1,4)-.beta.-glucanases. Hybrid fusion genes encoding Bacillus (1,3-1,4)-.beta.-glucanases were constructed, the gene products of which are more thermostable than any (1,3-1,4)-.beta.-glucanase known until now. The hybrid genes were constructed by reciprocal exchanges of the amino-terminal and carboxy-terminal parts of the .beta.-glucanase encoding genes from Bacillus amyloliquefaciens and Bacillus macerans. The resulting thermostable (1,3-1,4)-.beta.-glucanases retain a significant enzymatic activity at temperatures exceeding 65.degree. C. and at pH values below 5.0.