Abstract
Barley starch was liquefied at 105–160 °C mass temperature, 40–65% water content, by Bacillus licheniformis α-amylase (Termamyl) in a Creusot-Loire BC 45 twin-screw high temperature-short time (HTST) extrusion cooker. The subsequent saccharifica-tion was carried out normally in a batch process with Aspergillus niger glucoamylase (0·18–1·2%, w/w, d.m.) at 60°·C, after dilution to 10–45% dry matter. The highest dextrose equivalent (DE)—94–95 (up to 97 in the supernatant) after 24 h saccharification of 30% (d.m.) extrudate — was obtained after starch was extrusion-liquefied at 125–135°C, 60% water, 12kg/h feed (d.m.), and 150r/min. When starch was saccharified semi-continuously immediately after extrusion by recycling the extrudate through a Contherm scraped-surface heat exchanger, a DE of 86–89 was attained in less than 4 h. The maximum ethanol production in 44 h from 22·5% (w/w, d.m.) syrup was obtained by a batch fermentation process with a syrup having low initial DE of about 58. About 95% conversion was achieved compared with about 79% conversion with a DE of about 81 and less than 76% with a DE about 97.
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