From the perspective of 2007, an important strategic crossroads in the means of providing bioenergy has been reached. A wide complement of technologies has been developed to process realistically available amounts of lignocellulosic materials on at least a semi-industrial scale preparatory to bioethanol production.156 A crucial component in this is the massively increased production and continued improvement of the “molecular machines” of cellulases (endoglucanases).157 Chem­ical (pyrolytic and thermal “cracking”) methodologies are being critically devel­oped for biomass substrates to generate synthesis/producer gas both as a direct energy source and as an intermediary stage for “green” chemical refineries.158 Despite these advances, simple wood-burning stoves for domestic use and furnaces for district heating projects still represent far larger energy gains than does any form of biofuel production.159

Nascent industrial facilities for lignocellulosic ethanol are focused on exploiting the supply of cereal crop waste materials — in particular, wheat straw — that together comprise only 30% of the presently available lignocellulosic biomass resources.151 Worldwide, the industry may have to adapt to a succession of different seasonally available feedstocks, each of which presents unique challenges to pretreatment processing; softwood trees are, for example, dominant contributors to vegetation in Canada, northern Europe, Russia, and Scandinavia, and have both dedicated and passionate advocates and a history of several decades of scientific research; their technoeconomic features and factors are discussed in chapter 4.

Biotechnology must, therefore, demonstrate that multiple carbon sources ( hexoses, pentoses, sugar acids, oligosaccharides) can be efficiently converted to ethanol, a proposal that flies in the face of the fermentation industry’s tradition of sim­ple (single), highly reproducible carbon inputs. Moreover, biochemical engineering solutions must be found to maximize the value extracted from the processed cel­lulose, hemicelluloses, and lignin. The former area is that of metabolic engineering, the latter that of bioprocess control; both are considered next as integral parts of evolving models and paradigms of bioethanol production.