Very high gravity (VHG) ethanolic brewing and fermentation: a research update

Abstract

There have been numerous developments in ethanol fermentation technology since the beginning of the new millennium as ethanol has become an immediate viable alternative to fast-depleting crude reserves as well as increasing concerns over environmental pollution. Nowadays, although most research efforts are focused on the conversion of cheap cellulosic substrates to ethanol, methods that are cost-competitive with gasoline production are still lacking. At the same time, the ethanol industry has engaged in implementing potential energy-saving, productivity and efficiency-maximizing technologies in existing production methods to become more viable. Very high gravity (VHG) fermentation is an emerging, versatile one among such technologies offering great savings in process water and energy requirements through fermentation of higher concentrations of sugar substrate and, therefore, increased final ethanol concentration in the medium. The technology also allows increased fermentation efficiency, without major alterations to existing facilities, by efficient utilization of fermentor space and elimination of known losses. This comprehensive research update on VHG technology is presented in two main sections, namely VHG brewing, wherein the effects of nutrients supplementation, yeast pitching rate, flavour compound synthesis and foam stability under increased wort gravities are discussed; and VHG bioethanol fermentation studies. In the latter section, aspects related to the role of osmoprotectants and nutrients in yeast stress reduction, substrates utilized/tested so far, including saccharide (glucose, sucrose, molasses, etc.) and starchy materials (wheat, corn, barley, oats, etc.), and mash viscosity issues in VHG bioethanol production are detailed. Thereafter, topics common to both areas such as process optimization studies, mutants and gene level studies, immobilized yeast applications, temperature effect, reserve carbohydrates profile in yeast, and economic aspects are discussed and future prospects are summarized.

Bioethanol Production from Cachaza as Hydrogen Feedstock: Effect of Ammonium Sulfate during Fermentation

“…Thus, several authors have shown that an increase in the substrate concentration leads to a higher ethanol production. A lower water concentration in the bioethanol stream corresponds to a lower energy consumption for bioethanol purification [12]. For instance, Lu et al [13] concluded that a proportional increase of final ethanol concentration was achieved between 10 wt % and 30 wt % solids, when corn stover was used as feedstock.…”

Effective ethanol production from whey powder through immobilizedE. coliexpressingVitreoscillahemoglobin

“…26,27 Enhancing ethanol production and tolerance of microorganisms are alternative research areas for economical ethanol production. (reviewed by Lin and Tanaka 28,[29][30][31] ) Included among these is immobilization of cells. Generally immobilization techniques are simple and low cost.…”

Fermentation efficiency of high-gravity rye mashes using pressureless starch liberation methods

“…), while the mash containing 21% DM reached the final concentration of ethanol at the level of 9.08 ± 0.37% vol. The rapid increase in ethanol concentration in the mashes indicates the proper course of fermentation, and additionally inhibits the growth of bacteria and wild yeasts (Puligundla et al 2011).…”