Solid state fermentation

Technology
Technology details
Name:	Solid state fermentation (SSF)
Category:	Biochemical processes and technologies
Feedstock:	Food waste, garden and park waste
Product:	Food products (e.g., citric acid, natto, sake, tempeh), biocides

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. Nutrient levels, C/N ratio, feedstock-to-inoculum ratio, pH and mixing can also be controlled. SSF 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, and antibiotics. SSF can be applied in many different fields, such as food and aroma production, production of medicines, waste treatment or environmental technology. One example of 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.

A Sake Brewery Museum Exhibition

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. A diversity of microorganisms can be used for SSF and therefore a wide range of substrates can be used as feedstock.

Food products

Fresh tempeh at the market in Jakarta, Indonesia – traditionally wrapped in banana leaves

As described above, the feedstock can be a food product, such as rice or wheat bran. Another traditional food product produced by SSF is Tempeh, cooked soy beans fermented by different Rhizopus fungi. Soy beans are also fermented by Bacillus subtilis ssp. natto to create a food product called Nattō. Other substrates can also be used, such as tofu dregs (okara), coconut dregs, different cooked beans and peanuts.

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.

Waste streams

Solid-state anaerobic digestion (SS-AD) is commonly used to treat waste streams with high solid content such as municipal solid waste and lignocellulosic biomass.

Other

Wood

Pre-treatment

Additives

Biochar

Heat

Cooking

Process and technologies

Solid state bioreactors

Tray bioreactor

"Tray bioreactors consist of a chamber containing individual trays that can be made of different materials, such as wood, bamboo, metal, and plastic. The trays typically have open tops and perforated bottoms, and are stacked one above another with a space in between to increase the availability of air. The trays are static beds that are mixed infrequently or not at all. Air is provided into the chamber and circulated around the trays with controlled humidity and temperature."

Packed-Bed Bioreactor

"Packed-bed bioreactors are typically tubular containers that are packed with particles of substrates and microorganisms and have a perforated bottom to support the packing materials. In a packed-bed bioreactor, packing materials are generally not mixed and forced aeration is provided. The specific design of packed-bed bioreactors varies in the following aspects:

1. The cross-section of the bioreactor may have different shapes.

2. The bioreactor can be vertical, horizontal, or at an angle.

3. Aeration may be provided from either the top or the bottom. Additional aeration can be supplied by inserting a perforated tube inside the bioreactor."

Products

Food products

• Citric acid
• Nattō
• Sake
• Tempeh

Enzymes

• Polygalacturonase
• α-Amylase
• Lipase
• Protease
• Laccase
• Etc.

Post-treatment

Nattō on rice

Technology providers

Technology comparison

Company name	Country	Technology category	Technology name	TRL	Capacity [kg/h]	Temperature [°C]	Feedstock: Food waste	Feedstock: Garden & park waste	Product: Food/Feed	Product: Biocides
Company 1	[Country HQ location]	[Technology category (if different sub-categories are defined this has to be specified here, the available categories can be found on each technology page under the chapter Process and technologies)]	[Technology name (the "branded name" or the usual naming from company side)]	[4-9]	[numeric value]		●	●	●	●
Company 2	[Country HQ location]	[(if different sub-categories are defined this has to be specified here, the available categories can be found on each technology page under the chapter Process and technologies)]	[Technology name (the "branded name" or the usual naming from company side)]	[4-9]	[numeric value]		●	●	●	●

ICSN-CNRS

ICSN-CNRS developed a solid-state fermentation unit (called Platotex) that offers 2m(2) of cultivation surface that combines automatic sterilization, cultivation, and drying steps. Platotex is also able to support liquid-state fermentation.

Solid state fermentation provider

General information
Company:	ICSN-CNRS
Country:	France
Contact:
Webpage:	http://pilotunit.com/technologies/innovative-technology/platotex
Technology and process details
Technology name:	Platotex	Technology category:	Conversion (Biochemical processes and technologies)
TRL:	4	Capacity:	2 M2 cultivation surface kg·h-1
Atmosphere:		Nutrients:
pH:		Pressure:	bar
Temperature:	°C	Other:
Feedstock and product details
Feedstock:		Product:

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Patents

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