Production of fuel alcohol from hull-less barley by very high gravity technology
1995
Very high gravity mashes (>30 g dissolved solids per 100 ml) were prepared from an experimental hull-less barley (SB90354) and fermented with active dry yeast. A maximum ethanol concentration of 17.1% (v/v) was realized in fermented mash, and a total ethanol yield of 443 L per tonne of barley (dwb) was obtained. To prevent excess viscosity during mashing, it was necessary to hydrolyze beta-glucan in ground barley using crude preparations of beta-glucanase or Biocellulase. While both these preparations possessed an endoglucanase activity, no measurable exoglucanase activity was detected. A typical mash prepared at a water-to-grain ratio of 3:1 and without hydrolysis of beta-glucan had a viscosity of 2,480 BU, while the viscosities of the mashes prepared after hydrolysis of beta-glucan with beta-glucanase or Biocellulase were 560 and 240 BU, respectively. Hydrolysis of beta-glucan not only reduced the viscosity of the barley mash but also released water bound and trapped by the beta-glucan gel. The free amino nitrogen (FAN) content of the barley mashes was high when compared to wheat mashes, and about 80% of this FAN was taken up by yeast. In spite of the high FAN content of the mash, an exogenously added nitrogen supplement stimulated yeast growth and fermentation.
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