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

J Ind Microbiol Biotechnol (2011) 38:11331144 DOI 10.1007/s10295-011-0999-3

REVIEW

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

Pradeep Puligundla Daniela Smogrovicova Vijaya Sarathi Reddy Obulam Sanghoon Ko

Received: 10 March 2011 / Accepted: 7 June 2011 / Published online: 22 June 2011 Society for Industrial Microbiology 2011

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 eVorts 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 eYciency-maximizing technologies in existing production methods to become more viable. Very high gravity (VHG) fermentation is an emerging, versatile one among such technologies oVering great savings in process water and energy requirements through fermentation of higher concentrations of sugar substrate and, therefore, increased Wnal ethanol concentration in the medium. The technology also allows increased fermentation eYciency, without major alterations to existing facilities, by eYcient 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 eVects of nutrients supplementation, yeast pitching rate, Xavour 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 eVect, reserve carbohydrates proWle in yeast, and economic aspects are discussed and future prospects are summarized.

Keywords Very high gravity (VHG) Brewing Ethanol fermentation Nutrient supplementation Starch substrates Immobilization Optimization studies

Introduction

In recent years, brewing and bioethanol industries have been more focused on implementing cost-cutting measures to remain proWtable during the economic downturn. One such measure is the adoption of emerging very high gravity (VHG) fermentation...