In foaming-dependent feeding, the feeding was initiated inresponse to a massive accumulation of foam on the surface of theculture broth. This apparently occurred because the substrate (palmoil) was consumed and no longer able to provide its antifoam-ing action. A microscopic examination of the culture samplesconfirmed an absence of oil droplets whenever massive foamingoccurred. Each time foaming occurred, 60 mL of the culture brothwas withdrawn and replaced with an equal volume of the freshmedium as explained above for the pH-stat feeding operation.