The stages to produce ethanol using a biological approach are: A "pretreatment" phase, to make the lignocellulosic material such as wood or straw amenable to hydrolysis Cellulose hydrolysis (that is, cellulolysis) with cellulases, to break down the molecules into sugars Separation of the sugar solution from the residual materials, notably lignin Microbial fermentation of the sugar solution Distillation to produce roughly 95% pure alcohol Dehydration by molecular sieves to bring the ethanol concentration to over 99.5% In 2010, a genetically engineered yeast strain was developed to produce its own cellulose-digesting enzymes.
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