Solid state fermentation

Solid state fermentation (SSF) is a type of fermentation with a low water content in the substrate. The solid substrate is inoculated with the culture and the cultivation is mostly performed under controlled conditions, such as controlled temperature, light and humidity. It is "a traditional cultivation technique of food technology and involves all cultivations of microorganisms on a solid substrate without free liquid phase." Besides traditional food processing methods, solid state fermentation is also used for the industrial production of a diverse range of other products, such as enzymes, biogas, pigments, antibiotics. SSF can be applied in many different fields, such as food and aroma production, production of medicines, waste treatment or environmental technology.

A Sake Brewery Museum Exhibition

One example for a traditional solid state fermentation is the production of Sake (a Japanese alcoholic beverage from rice). The polished and cooked rice serves as the solid substrate of the first fermentation step in the Sake production process. It is inoculated with Kōji-kin (Aspergillus oryzae) spores. A. orizae is a fungus which converts the starch from the rice to sugar. After this solid state fermentation, a liquid state fermentation step follows during which yeast converts the sugar to ethanol.

Feedstock

Origin and composition

Solid state fermentation is especially suitable for the cultivation of filamentous organisms, like ascomycetes and basidiomycetes, but also for various yeasts and bacteria. As diverse as these microorganisms are also the possible substrates and thus feedstocks.

Food products

As described above, the feedstock can be a food product, such as rice or wheat bran.

Agro-industrial residues

Agro-industrial residues such as cassava bagasse are e.g. used for the production of citric acid via SSF. Citric acid is industrially produced by using the filamentous fungus Aspergillus niger. A wide range of agro-industrial residues can be used for the production of citric acid, such as apple and grape pomace, carrot waste, carob pod, orange and pineapple waste, cassava bagasse, coffee husk, kiwifruit peel, mussel processing wastes, okara (soy residue), rice and wheat bran.

Other

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