Foams

Foam can be defined as a gas dispersed in a liquid at a ratio such that the mixture's bulk density approaches that of a gas rather than a liquid (1). Foaming can occur for several reasons, stemming from both mechanical and chemical origins. Examples of mechanical contributors of foam formation are agitation near a gas-liquid interface, excessive vacuums or pressure gradients, or the free fall of liquids (2). The addition of certain chemicals that act as surface-active materials, or surfactants, may also produce foaming within a process. The existence of starch in a food process is an example of this. Foam formation can cause many problems within a process, including reducing the capacity of open vats, increasing the need for head space in closed systems, slowing the time needed to drain liquids or dried foods, interfering with process instruments, or it can increase housekeeping costs by introducing the need for maintenance personnel to deal with safety hazards such as slippery floors and the overflowing of process tanks (2).

Two basic actions can be taken to stop the formation of foam in a food process. The first involves mechanical means of eliminating the foam, such as heating, centrifug-ing, spraying, or ultrasonic vibration (3). The other option is to introduce chemical antifoams or defoamers to the process. This article will focus on the chemical method of foam control. Defoamers are materials that specialize in destroying existing foam immediately. Antifoams are materials that are designed as long-lasting means of preventing the formation of foam. Examples of foam control products range from liquid products such as hydrocarbons (kerosene, vegetable oils, organic phosphates, and acetylenic glycols), polyethers, fluorocarbons, and silicones, to solid products such as fatty amides, hydrocarbon waxes, solid fatty acids, and esters (3). The remainder of this article will focus on silicone-based antifoam products.

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