NOVELTY - Improving the final yield from, or efficiency of, a fermentation reaction comprising plant material that is acetylated, comprises: enzymatically or chemically degrading plant material from a mutant CAS1L plant that has decreased activity of at least one Cas1L gene to obtain degradation products; and fermenting the degradation products in a fermentation reaction, where the final yield, or efficiency of the fermentation reaction is increased relative to the final yield of a fermentation reaction using corresponding plant material from a wildtype Cas1L plant.    USE - The method is useful for improving the final yield (or efficiency) of a fermentation reaction (claimed), where the final yield is a biofuel including ethanol.    ADVANTAGE - The method: utilizes genetically engineered or mutant CAS1L plant that has decreased activity of Cas1L gene (i.e. reduced acetylation) and thus provides improved (increased) final yield (biofuel production) in the fermentation reaction, when compared to the final yield of a fermentation reaction comprising plant material from a wildtype Cas1L plant.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a plant comprising a vector that comprises an RNA interference (RNAi) that inhibits a Cas1L gene;    (2) an isolated mutant Cas1L plant in which expression of at least two Cas1L genes is inhibited;    (3) a method of engineering a plant to reduce acetylation in the cell wall of a plant, comprising inhibiting expression of at least one Cas1L gene in the plant using RNAi;    (4) bulk harvested material comprising material from at least two engineered plants that have decreased expression of at least one Cas1L gene;    (5) a plant engineered to have reduced expression of at least one Cas1L gene, where the plant has at least 10% reduction in cell wall acetylation in comparison to a plant that has not been engineered;    (6) a polysaccharide or polysaccharide fraction isolated from the above plant;    (7) a food ingredient containing the polysaccharide; and    (8) a food product containing the food ingredient.