Abstract: A process is disclosed for continuously producing erythritol by cultivating erythritol-producing microorganisms under aerobic conditions. The process comprises the steps of: maintaining the concentration of dissolved oxygen in a culture broth in a fermentation tank at not less than 0.2 ppm; separating a part of the culture broth into a concentrated liquid in which the concentration of cells is increased and a clarified liquid by a cell separator; returning the concentrated liquid to the fermentation tank; controlling an amount of the clarified liquid to be extracted outside an erythritol-producing system and an amount of the culture broth and/or the concentrated liquid to be extracted outside the producing system such that the concentration of the cells in the culture broth in the fermentation tank may be kept in a range from 40 to 200 g/l when calculated as a weight of dried cells; and recovering erythritol from the clarified liquid.

Abstract: An air diffuser has a non-porous rigid plate mounted on an air chamber to permit diffusion of air to the outside of the chamber, which porous plate has a smooth outer surface and diffusing pores extending therethrough, more than 95% of the diffusing pores having diameters within .+-.20% of a nominal diameter selected in a range of 50-300 .mu.m.