A great number of molds are able to produce ethanol. The filamentous fungi Fusarium, Mucor, Monilia, Rhizopus, Ryzypose, and Paecilomyces are among the fungi that can ferment pentoses to ethanol [33]. Zygomycetes are saprophytic filamentous fungi, which are able to produce several metabolites including ethanol. Among the three genera Mucor, Rhizopus, and Rhizomucor, Mucor indicus (formerly M. rouxii) and Rhizopus oryzae have shown good performances on ethanol productivity from glucose, xylose, and wood hydrolyzate [60]. M. indicus has several industrial advantages compared to baker’s yeast for ethanol production, such as (a) capability of utilizing xylose, (b) having a valuable biomass, e. g., for production of chitosan, and (c) high optimum temperature of 37°C [61]. Skory et al. [62] examined 19 Aspergilli and 10 Rhizopus strains for their ability to ferment simple sugars (glucose, xylose, and arabinose) as well as complex substrates. An appreciable level of ethanol has been produced by Aspergillus oryzae, R. oryzae, and R. javanicus.

The dimorphic organism M. circinelloides is also used for production of ethanol from pentose and hexose sugars. Large amounts of ethanol have been produced during aerobic growth on glucose under nonoxygen — limiting conditions by this mold. However, ethanol production on galac­tose or xylose has been less significant [63]. Yields as high as 0.48 g/g ethanol from glucose by M. indicus, under anaerobic conditions, have been reported [64]. However, the yield and productivity of ethanol from xylose is lower than that of P stipitis [65].

Although filamentous fungi have been industrially used for a long time for several purposes, a number of process-engineering problems are associated with these organisms due to their filamentous growth. Problems can appear in mixing, mass transfer, and heat transfer. Furthermore, attachment and growth on bioreactor walls, agitators, probes, and baffles cause heterogeneity within the bioreactor and prob­lems in measurement of controlling parameters and cleaning of the bioreactor [66, 67]. Such potential problems might hinder industrial application of M. indicus for ethanol production. However, this fungus is dimorphic, and its morphology can be controlled to be yeast-like or pellet-like through fermentation [65].