Biochemical Engineering Journal 13 (2003) 81–84 Solid-state fermentation Ashok Pandey ∗ Biotechnology Division, Regional Research Laboratory, Council of Scientific and Industrial Research, Trivandrum-695 019, India Received 15 November 2001; accepted after revision 24 July 2002 Abstract Solid-state fermentation has emerged as a potential technology for the production of microbial products such as feed, fuel, food, industrial chemicals and pharmaceutical products. Its application in bioprocesses such as bioleaching, biobeneficiation, bioremediation, biopulping, etc. has offered several advantages. Utilisation of agro-industrial residues as substrates in SSF processes provides an alternative avenue and value-addition to these otherwise under- or non-utilised residues. Today with better understanding of biochemical engineering aspects, particularly on mathematical modelling and design of bioreactors (fermenters), it is possible to scale up SSF processes and some designs have been developed for commercialisation. It is hoped that with continuity in current trends, SSF technology would be well developed at par with submerged fermentation technology in times to come. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Solid-state fermentation; General aspects; Biochemical engineering aspects; Modelling; Design of bioreactor 1. Introduction Solid-state fermentation (SSF) is defined as the fermen- tation involving solids in absence (or near absence) of free water; however, substrate must possess enough moisture to support growth and metabolism of micro-organism [1–4]. SSF stimulates the growth of micro-organisms in nature on moist solids and has been credited to be responsible for the beginning of fermentation technique in ancient time [5]. It is, therefore, not surprising that almost all the fermentation processes used in ancient time were based on the principles of SSF. SSF offers numerous opportunities in processing of agro-industrial residues. This is partly because solid-state processes have lower energy requirements, produce lesser wastewater and are environmental-friendly as they resolve the problem of solid wastes disposal. A glance at the history of fermentation technology in- dicates that the SSF processes were nearly completely ig- nored in western countries after 1940 due to adaptation of submerged fermentation (SmF) technology. However, per- haps there was no logical reasoning for this at that time. Since the development of penicillin took place in SmF and due to enormous importance of penicillin during the world war, SmF became a role model technology for production of ∗ Tel.: +91-471-515-279; fax: +91-471-491-712. E-mail addresses: pandey@csrrltrd.ren.nic.in, ashokp 56@hotmail.com (A. Pandey). any compound by fermentation. Subsequently, researchers of that time put their entire attention on SmF and probably unknowingly SSF was neglected. Still in the isolated pockets research continued on SSF systems and during 1950–1960, steroid transformation was reported using fungal cultures. The trend continued, although slowly and SSF attained an- other milestone during 1960–1970 when reports appeared on mycotoxins production by SSF. Production of protein en- riched cattle feed was the next major activity reported, which involved utilisation of agro-industrial residues, thus offering a unique process development for value-addition of these otherwise low cost residues (and to some extent environment pollutants). In fact, this was one of the areas, which gen- erated interest of researchers globally on SSF. Since then, there has been continuous increase in the extension of SSF arena, which picked up strongly during the last one decade. A large numbers of patents and publications have appeared on fundamental aspects of SSF, development of bioreactors (fermenters), modelling and on production of various micro- bial products such as food, feed, various primary and sec- ondary metabolites, and bioprocesses such as bioleaching, biopulping, bioremediation, biobeneficiation, etc. [6–12]. 2. General aspects of SSF There are several important aspects, which should be con- sidered in general for the development of any bioprocess in 1369-703X/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S1369-703X(02)00121-3