GRASS AS A SOURCE OF FERMENTABLE CARBOHYDRATE FOR ETHANOL-PRODUCTION

Field plot experiments were conducted between 1986 and 1989 to measure water-soluble carbohydrate (WSC) production from five Lolium multiflorum cultivars and from seventeen other cultivars, representative of Lolium multiflorum x Lolium perenne hybrids, Lolium perenne, Festuca arundinacea, Dactylis glomerata and Phleum pratense. Harvested grass was macerated and subjected to hydraulic pressure to obtain grass juice containing soluble sugars. Juice was subjected to acidic conditions, then fermented to ethanol, using yeast. It was shown to be necessary to pre-treat extracts at pH 2 for 15 min at 90-degrees-C in order to optimise ethanol production. Average annual yields of WSC in Lolium multiflorum totalled 5.05, 2.94 and 2.80 t/ha in 1986, 1987 and 1988, respectively. Using mean extraction and sugar to ethanol conversion ratios these yields convert to an ethanol production of 1666, 984, and 987 l/ha for 1986, 1987 and 1988, respectively. Yields of WSC from other Lolium and Festuca arundinacea were little more than half of the yields from Italian ryegrasses. Dactylis glomerata and Phleum pratense yielded less again. Grass residue remaining after juice extraction had less than half the water of harvested grass, slightly higher nitrogen content and its dry matter digestibility was lowered by 2-5%.