U.S. Department of Energy - Energy Efficiency and Renewable Energy
Biomass Program
Fermentation Background
The earliest attempts to utilize wood sugars from acid hydrolysis included fermentation of the sugars to ethanol. Ethanol plants operated here in the United States during World War I achieved yields of ethanol of around 20 to 25 gallons per dry ton of mill waste processed. This low yield is due mostly to low yields in sugar.
During World War II, researchers at USDA developed the Madison Wood Sugar Process. They reported results on fermentation of Douglas-fir hydrolyzates using the yeast Saccharomyces cerevisiae, an industrial work-horse as far as fermentation is concerned. Like many researchers since, they struggled with problems of inhibitors in the hydrolyzate that affected yield and productivity.
Removal of furfural, treating with aluminum chloride, and use of large inocula eliminated these problems. Yields of 39% to 40% of total reducing sugars were achieved in as little as 15 hours. The greatest impact on yield was the inability to ferment the five carbon sugars from hemicellulose. This problem remained unresolved for several decades.
In the 1980s, research on xylose fermentation began to bear fruit. A number of wild type yeast were identified that could convert xylose to ethanol. But, these organisms required carefully controlled levels of oxygen. With the advent of powerful genetic engineering tools, we now have access to genetically engineered bacteria and yeast capable of fermenting both the five- and six- carbon sugars.
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