Inoculation methods and aeration conditions in the production of pellet cultures of Aspergillus niger 110 with acceptable citric acid yields were studied. Inoculating the fermentor with a preculture of pellets, instead of directly with spores, and carrying out fermentation at 1000 rev min−1 from seeding resulted in fungus growth in the form of compact, smooth pellets of uniform size and excretion of 48.0 g l−1 of citric acid. In contrast, cultivation of this same type of inoculum at 450 rev min−1 for the first 48 h, followed by 1000 rev min−1 for the remainder of the fermentation period, gave rise to different types of pellets of varying size that yielded only 30.3 g l−1 of citric acid. Under these latter aeration conditions, increasing the air flow from 0.9 to 1.3 vvm raised the citric acid yield to 48.7 g l−1 while leaving fungus morphology unaffected. Peer reviewed