The effectiveness of an inverted hollow spinning cone (IHSC) for controlling foam and liquid hold-up is demonstrated in pilot scale equipment for a currently commercially exploited recombinant Bacillus fermentation with the characteristically challenging foaming and hold-up issues of this genus. The cone rotates on the existing agitator shaft at the normal production operating level. A series of 9 trials were conducted in 550-1 pilot scale fermenters: 2 fermentations without foam control agent (FCA) addition, 4 controls with FCA addition on demand, and three with the cone as the sole method of level control. Batches running without FCA addition or the use of an IHSC lost 52 +/-15 kg of broth through the exhaust system. Batches with FCA addition on demand or the IHSC ended with a statistically indistinguishable filling of 308 +/- 6 kg and 319 +/- 13 kg, respectively. Process performance in terms of enzyme titre was not affected. Such encouraging results indicate great potential savings in both fermentation and recovery costs since FCA addition can be completely avoided. A full-scale production evaluation is justified. (c) 2004 Elsevier Ltd. All rights reserved.