NOVELTY - Mutant thermostable glycosyl hydrolase family 7 enzyme including endoglucanase enzyme, preferably Trichoderma reesei endoglucanase I, comprising a serine, threonine, leucine, or methionine at an amino acid which aligns with the amino acid 230 of SEQ ID NO.1, where sequences not defined here may be found at ftp://ftp.wipo.int/pub/published-pct-sequences/publication, is new.    USE - The enzyme is useful: in hydrolyzing or degrading a biomass including crystalline cellulose, or lignocellulosic plant material, where the plant material is Miscanthus, energy grass, elephant grass, switch grass, cord grass, rye grass, reed canary grass, common reed, wheat straw, barley straw, canola straw, oat straw, corn stover, soybean stover, oat hulls, sorghum, rice hulls, sugarcane bagasse, corn fiber, distillers dried grains with solubles, blue stem, corncobs, pine, willow, aspen, poplar wood, or energy cane; in fermentative production of biofuels, processing of food, polishing and cleaning of textiles, production of polished crystalline cellulose, bleaching of paper pulp, and laundry detergent composition; and as a food additive (all claimed) for mono-gastric animals such as poultry, swine, and for human food.    ADVANTAGE - The enzyme is able to hydrolyzing lignocellulose efficiently at higher temperatures, and exhibits increased activity/thermostability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) the preparation of the mutant thermostable enzyme;    (2) an isolated nucleic acid encoding the mutant thermostable enzyme;    (3) an expression vector comprising the nucleic acid operably linked to a regulatory sequence;    (4) a host cell comprising the expression vector;    (5) producing the mutant thermostable enzyme;    (6) a composition comprising the host cell and culture medium, or mutant thermostable enzyme in the supernatant of the culture medium;    (7) reducing the viscosity of a pretreated biomass mixture, comprising contacting a pretreated biomass mixture having an initial viscosity with the composition, and incubating the contacted biomass mixture under conditions sufficient to reduce the initial viscosity of the pretreated biomass mixture;    (8) converting biomass to sugars comprising contacting the biomass with the composition;    (9) hydrolyzing or degrading a biomass, comprising contacting the biomass with the composition;    (10) producing a fermentation product, comprising contacting biomass with the composition to form a first product, and culturing the first product with one or more fermentative microorganisms under conditions sufficient to produce a fermentation product, or incubating the first product with a chemical solution under conditions sufficient to produce a fermentation product by a chemical process;    (11) fermenting biomass, comprising contacting the biomass with one or more fermentative microorganisms, where the biomass is treated by the composition;    (12) producing a fuel comprising contacting a biomass with the composition to yield a sugar solution, and culturing the sugar solution with a fermentative microorganism under conditions sufficient to produce a fuel, or incubating the sugar solution with a chemical solution under conditions sufficient to produce a fuel by a chemical process;    (13) food processing, comprising contacting a plant material with the composition to yield digestible plant material;    (14) textile polishing comprising contacting a textile with the composition to yield a polished textile;    (15) textile cleaning comprising contacting a soiled textile with the composition to yield a clean textile;    (16) paper pulp bleaching comprising contacting paper pulp with the composition to yield bleached paper pulp;    (17) producing polished crystalline cellulose comprising contacting crystalline cellulose with the composition to yield polished crystalline cellulose;    (18) a laundry detergent composition comprising the enzyme and a detergent; and    (19) a food additive comprising the enzyme.