Chapter VII Anti-Foam Agents

Abstract

Publisher Summary This chapter describes methods of foam prevention and destruction in fermenters, with particular reference to the use of chemical anti-foam agents. Several fermentations require high rates of aeration and vigorous stirring if they are to yield their best. These conditions, imposed on the types of nutrient solutions commonly employed, provide an ideal situation for foam formation. The most obvious problem created by foaming is that the effective volume of the batch in the fermenter increases. The classical definition of foam is that it is a dispersion of gas in liquid, with the liquid in the form of thin films separating gas bubbles. The chapter focuses on general principles of foam destruction, and the general properties of anti-foam agents. The chapter compares the theory of Gibb and Marangoni. The measure most frequently required is an indication of how much a particular broth will foam, or expand, under the conditions of aeration and agitation within an actual fermenter. One advantage of mechanical foam destruction is that no extraneous agents need be added to the system. The simplest form of internal foam breaker consists of rotating paddles or vanes attached to the stirrer shaft. Vegetable oils have long been used in fermentation to suppress foam formation, and in addition they often serve to control pH because they are metabolized.