Solid State Fermentation (SSF) is the cultivation of micro organisms under controlled conditions in the absence of free water. • Examples of products of Solid State Fermentation include industrial enzymes, fuels and nutrient enriched animal feeds.
SSF PROCESS METHODOLOGY In any SSF process the basic steps carried out are: 1. The preparation of a solid substrate 2. Sterilization of the substrate. 3. Rising of suitable inoculum. Traditional or pure culture technique. 4. The inoculation of the moist substrate 5. The incubation in appropriate culture of vessels or reactors.
6. Maintenance of optimal conditions. (pH, T, mixing, aeration, flow pattern) 7. Harvesting of solids 8. Drying / Extraction of product 9. Further downstream processing if necessary.
Bioreactors Used for Solid-substrateFermentations • Most solid-substrate fermentations are batch processes. • Some processes do not require bioreactors; they simply involve spreading the substrate onto a suitable floor.
Substrate characteristics • Excessive water tends to aggregate solid particles making aeration difficult • Low moisture environment favors growth of yeast and fungi • During fermentation water activity is controlled by aeration with humid air and sometimes by intermittent spraying of water.
The size of substrate effects • The extent of micobial colonization • Air penetration • Downstream extraction Small particles are preferred because they present a relatively large surface area for microbial action.
Koji Fermentations • These are typical examples of SSF • Koji comprises of soy beans or grain on which mould is growing
The production of soy sauce,miso and sake involves koji fermentation Miso- fermented soyabean paste smells and tastes like soy sauce. Sake bottles Miso soup
Koji is made by sprinkling seed koji over steamed rice, barley, or soybeans and cultivating the fungus under temperature conditions suitable for its growth. As the fungus propagates, enzymes break down the grains' starch and proteins into sugars and amino acids. The most important enzymes in a koji are alpha amylase, glucoamylase and acid protease
Koji being cultivated in small trays Sake barrels
The Manufacturing Process of Soy sauce • Brewing, the traditional method of making soy sauce, consists of three steps: koji-making, brine fermentation, and refinement Koji-making • Carefully selected soybeans and wheat are crushed and blended together under controlled conditions. Water is added to the mixture, which is boiled until the grains are thoroughly cooked and softened
The mash, as it is known, is allowed to cool to about 80°F (27°C) before a proprietary seed mold (Aspergillus) is added. • The mixture is allowed to mature for three days in large perforated vats through which air is circulated. • This resulting culture of soy, wheat, and mold is known as koji.
Brine fermentation • The koji is transferred to fermentation tanks, where it is mixed with water and salt to produce a mash called moromi • Lactic acid bacteria and yeasts are then added to promote further fermentation
The moromi must ferment for several months, during which time the soy and wheat paste turns into a semi-liquid, reddish-brown "mature mash.“ • This fermentation process creates over 200 different flavor compounds
Refinement • After approximately six months of moromi fermentation, the raw soy sauce is separated from the cake of wheat and soy residue by pressing it through layers of filtration cloth • The liquid that emerges is then pasteurized. The pasteurization process serves two purposes. It helps prolong the shelf life of the finished product, and it forms additional aromatic and flavor compounds. Finally, the liquid is bottled as soy sauce.
shōyu (koikuchi) and light colored shōyu (usukuchi) as sold in Japan by Kikkoman, 1 litre bottles.
Tray fermenter: simple type fermenter used in small and medium scale in Asia Trays with perforated mesh made of wood are used Inoculation and occasional mixing are done manually Solid state fermenters
Bed systems, as used in commercial koji production consisting of a bed of substrate up to 1 m deep, through which humidified air is continuously forced from below Static bed fermenter
Bed solids depth is not more than0.5m. It is highly automated Tunnel fermenter
The cylindrical drum of rotary fermenter is supported on rollers and rotated at 1-1.5rpm along the axis . Rotation may be intermittent and speed may vary with fermentation stage Rotary drum fermenter
These fermenters are used in enzyme and microbial-biomass production. Their main disadvantage is that the drum is filled to only 30% capacity, otherwise mixing is inefficient.