"The big plus for softwoods, including pine, is that they have a lot of sugar that yeast can use," she said. "Yeast are currently used in ethanol production from corn or sugarcane, which are much easier materials for fermentation; our process increases the amount of ethanol that can be obtained from pine."
Before the pinewood is fermented with yeast, however, it is pre-treated with heat and chemicals, which help open the wood for enzymes to break the cellulose down into sugars. Once sugars are released, the yeast will convert them to ethanol, but compounds produced during pretreatment tend to kill even the hardiest industrial strains of yeast, making ethanol production difficult.
The new strain of yeast is capable of producing ethanol in fermentations of pretreated wood containing as much as 17.5 percent solid biomass. Previously, researchers were only able to produce ethanol in the presence of 5 to 8 percent solids. Studies at 12 percent solids showed a substantial decrease in ethanol production.
This is important, said Doran-Peterson, because the greater the percentage of solids in wood, the more ethanol that can be produced. However, a high percentage of solids also places stress on the yeast.
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