Yeasts

Yeasts have been chosen in the great majority of cases for cultivation in distillery stillages of different origin. They have been commonly used in food preparation for thousands of years so there are no prejudices regarding their use for food or feed, as is the case with bacteria and molds. The quick growth of yeasts lead to advantages of time and low cost, as well as limited possibility of contamination by other microorganisms. The fermentation process is easy to handle and continuous cultivation is possible. The use of yeast is interesting because of its low price and its high protein and vitamin content. However, some facts must be taken into account (Huyard et al. 1986): (a) the yeast should not contain high levels of contaminants, if it is to be used for feed, (b) energy is needed for separating the yeast from the substrate, (c) effective aeration is necessary, and (d) the remaining effluent still has a high COD and needs to be treated in a sewage treatment facility.

Candida (Torula) is the fungal organism most used for molasses stillages and to a lesser extent for other distillery effluents. Other yeasts are also suitable for bioconversion of molasses stillage. In screening for a useful yeast, Hansenula, Debaromyces, and Rhodotorula were selected out of 203 strains (Akaki et al. 1981). Hansenula spp. (Moriya et al. 1990; Shojaosadati et al. 1999) and Debaromyces sp. (Selim et al. 1991) were also successful as were Saccharomyces cerevisiae (Selim et al. 1991), Kluyveromyces spp. (Braun and Meyrath 1981; Selim et al. 1991), Pichia tainania (Chang and Yang 1973; Lin et al. 1973) and Phaffia rhodozyma (Fontana et al. 1997). Rhodotorula glutinis produced biomass for fodder rich in vitamin B on raisin vinasse (Aran 1977; Yazicioglu et al. 1980). A distillery effluent from rice spirit production could be successfully reused by a S. cerevisiae strain (Yang and Tung 1996).

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