Typically for newly-developed processes, plastic bags will be used, employing special plastics that allow the exchange of O2 and CO2, but do not allow the exchange of water, thus allowing the microorganism to respire but preventing the bed from drying out. The great advantage of this system over the traditional technology of open trays is that the plastic prevents contaminants from entering the bed. Either the whole bag may be made of this plastic, or the bag may be made of a gas-impermeable plastic and have a "window" made of a special plastic, paper, or fabric. This technology has been used for over 20 years to produce spore inoculum for the koji process (Lotong and Suwanarit 1983), although of course it is not an appropriate technology for the production of soy sauce koji itself in modern processes, where individual batches are of the order of several tons. However, it may be appropriate if smaller volumes are produced. For example, in Australia, a biopesticide based on spores of Metarhizium anisopliae is produced on rice grains within "self-aerating bags" (Milner 2000). In 1999, at the commercial trial stage, 9 tons of product was produced, which corresponds to a productivity of 25 kg per day, averaged over 365 days.
Cuero et al. (1985) used micro-porous plastic bags, consisting of polypropylene with 0.4 |im pores. The bags can be autoclaved. They allow gas and water vapor exchange, but neither the release of spores nor the entry of contaminants. Due to the fact that the bags allowed water vapor exchange, the bags were incubated in a high humidity environment (95% relative humidity).
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