Group I bioreactors, or "tray bioreactors", represent the simplest technology for SSF. They have been used for many centuries in the production of traditional fermented foods such as tempe and in the production of soy sauce koji. However, this chapter does not review these applications. Readers interested in traditional fermented foods should consult the reading listed at the end of the chapter. The current chapter considers tray bioreactors as candidates in the selection of bioreactors for newly-developed SSF processes. Trays may be appropriate for a new process if the product is not produced in very large quantities, if a "produced-packet" of fermented product can be sold directly, or if labor is relatively cheap.
The basic design features of tray-type bioreactors have already been presented in Chap. 3.3.1. Figure 6.1 shows these features in more detail. Some possible variations in the design include:
• the tray chamber may be relatively small, such as an incubator, or it may be a room large enough for people to enter;
• the tray may be constructed of various different materials, such as wood, bamboo, wire or plastic. In fact, a plastic bag might be used instead of a rigid tray;
• the bottom and sides of the tray may be perforated or not;
• water-cooled heat exchange surfaces might be incorporated.
The available design features for tray-type bioreactors are:
• the dimensions of the tray, namely length, width, and height;
• the positioning of the trays within the bioreactor;
• the presence of cooling surfaces within the tray chamber.
The available operating variables are:
• the temperature, humidity, and flow rate of the air entering the tray chamber and the velocity of circulation past the tray surface;
• if cooling surfaces are present, then the temperature of the cooling water.
Note that, although this type of bioreactor is nominally static, the bed may be mixed infrequently. For example, it is typical for the tray contents to be turned by hand once or twice per day.
tray room incubator tray room incubator
Fig. 6.1. Basic design features of tray-type bioreactors and possible design variations. (a) Different tray chambers, including tray rooms and incubators, in which the trays are arranged on shelves. (b) Different basic tray designs. The tray on the left could be made of wood, plastic, bamboo, or wire. The plastic bag on the right could be made entirely of a gas-permeable plastic, or could contain a filter insert that allows gas exchange
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