Circulation time distribution fermentation

Fnnahashi, H., H. Harada, H. Tagnchi, and T. Yoshida (1987a). Circulation time distribution and volume of mixing regions in highly viscous xanthan gum solution in a stirred vessel, 7. Ferment. Technol, 20, 277-282. 

Funahashi, H., K. I. Hirai, T. Yoshida, and H. Taguchi (1988a). Mixing state of xanthan gum solution in aerated and agitated fermenter effects of impeller size on volumes of mixed regions and circulation time distribution, J. Ferment. Technol, 66, 103-109. 

Internal circulation patterns and turbulence. Sasakura et al. (138) and Rachez et al. (139) investigated internal age distributions by means of tracers and proposed representative models of the circulation pattern. Bryant and coworkers (135, 140, 141) and Reuss studied more specifically circulation times in large stirred tanks by using radio flow-followers (aiming at applications for fermenters > 0.5 m ). They showed that circulation times tQ were log-normally distributed ... 

Oosterhuis et al. (1985) reported a mean circulation time of approximately 12 s in an unaerated 19 m fermenter using a radio pill flow follower. The experimental cumulative CTD associated with this mean is shown in Figure 18-7. This is the distribution of the residence time of the liqnid outside the impeller region. If it is... 

Fermentation. The term fermentation arose from the misconception that black tea production is a microbial process (73). The conversion of green leaf to black tea was recognized as an oxidative process initiated by tea—enzyme catalysis circa 1901 (74). The process, which starts at the onset of maceration, is allowed to continue under ambient conditions. Leaf temperature is maintained at less than 25—30°C as lower (15—25°C) temperatures improve flavor (75). Temperature control and air diffusion are faciUtated by distributing macerated leaf in layers 5—8 cm deep on the factory floor, but more often on racked trays in a fermentation room maintained at a high rh and at the lowest feasible temperature. Depending on the nature of the leaf, the maceration techniques, the ambient temperature, and the style of tea desired, the fermentation time can vary from 45 min to 3 h. More highly controlled systems depend on the timed conveyance of macerated leaf on mesh belts for forced-air circulation. If the system is enclosed, humidity and temperature control are improved (76). 

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