BURSTING THE BUBBLES

The perfect blend of foam and defoamer is essential in potato processing as Andre Erasmus finds with the help of Emerald Foam Control’s Frank Magazine.

Foam is all around us – it can be in a bubble bath or the head of your freshly poured beer where it is fun; or it can be useful in mineral processing, waste water treatment, fire prevention or food processing. But it can also be a nuisance and, for effective potato processing, foam control is vital.

Foams consists of a matrix of lamellas which are gases encapsulated with different forms of liquids. Their formation depends on the presence of surfactants, which are by definition, located at the liquid surfaces. 

The term ‘surfactant’ is a blend of ‘surface acting agent’ and was coined in 1950. Surfactants reduce the surface tension of water by adsorbing at the liquid interface. Adsorption is a process that occurs when a gas or liquid accumulates on the surface of a solid or a liquid (adsorbent), forming a film of molecules or atoms. It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution.

If air is introduced into a liquid containing a surfactant, thereby agitating it, the surfactant molecules form a double layer around the gas forming a bubble. Repeating this process results the formation of a matrix of lamellas which produce foam.
Foam is stable if the energy of the system is low and the forces within the foam are in equilibrium. Spherical lamellae are not stable because of their high liquid content. Surface tension and other mechanical stresses therefore cause spherical lamellae to link together so that they share surfaces, and the result is a ‘polyhedral’ foam that is more stable.

Total equilibrium is energetically impossible, however, so even polyhedral foam will sooner or later self-destruct. The collapse of foam has three stages: drainage of liquid from between the lamellae, rupture of the lamellae, and the diffusion of gas out of the foam cells.

Foam in food

Foam is generated in many commercial processes. Some of the more common processes are: food processing, chemical manufacturing, fermentation, textile, adhesive manufacturing, printing inks, paints, coating and resins and wastewater management. If it were not for a defoamer the processing of many of the products we depend upon today would be difficult to impossible of the quality of products would be poor.

Defoamers are used to either control foam formation or eliminate foam from forming during the manufacturing process.
When the formation of foam is prevented, the chemical is usually referred to as antifoam. When foam is already present and the product is added to destroy foam, this is a defoamer application.

Foam can be generated by either mechanical agitation or through a chemically influenced mechanism, such as fermentation process, for example.

Defoamers are manufactured and engineered to work in specific environments. Environments in which defoamers are expected to work could include ranges of temperature, pH, pressure or chemical constituent’s compatibility. Defoamers may even be required to meet certain regulations such as The Food and Drug Administration Code of Federal Regulations, HACCP, cGMP, EPA, National Science Foundation, Halal, Kosher or Kosher for Passover Certification, or just be used for industrial applications meeting local, state, and federal guidelines. Depending on each state or country, the laws are specific and govern the defoamer’s selection and application.

Under control

Turning to potato processing specifically, it is essential that foam formation is controlled.

As Frank Magazine, business director for Emerald Foam Control points out, there needs to be the perfect blend of foam and defoamer to make the processing of potato products work efficiently and economically . “It’s all about control,” he said. “Foam in potato processing is caused by starch and biological components which are particularly challenging.”

Selection criteria for foam control include:
Effectiveness – it must control foam in the process and in some cases the end-use;
Compatibility – must not impact on the finished product’s appearance;
Persistence – must work throughout the processing steps and time period as well as possibly over the shelf life of the finished product; and
Efficiency – must work at a low dosage.

Magazine points out that, in potato processing, the application can be either a defoaming ore anti-foaming product. This is based on the application feedpoint in the system. The vital point is that the product destroys the foam build up (knock down) for an extended period (hold down).

“A defoamer produces a mechanism which causes the collapse of foam, said Magazine.
“It causes spreading, drainage, thinning and then rupture of the lamellae.
“A careful marriage of foam with foam control is what works, there needs to be a balance between insolubility and dispersability with each formulary ingredient providing a specific function.”
So the marriage needs to have that perfect chemistry.
Some of the main components of a defoamer’s chemistry are its liquid phase, emulsifier, spreading agent and its hydrophobic particle.

The liquid vehicle – oil (vegetable or mineral), water, polyol (alcohol based) or an ester (chemical based) – must have a degree of incompatibility with the media it has to work in and also needs a rapid spreading coefficient to roll back water from hydrophilic surfaces.

The spreading agent (usually esters, oils or wetting agents) has the job of spreading the defoamer and giving it the ability to enter the specific make up of bubbles it will encounter.

The hydrophobic particle (silica or waxes) must fill gaps and prevent foam from reforming. The particles need to rest at a specific contact angle in the foam matrix and must be of the correct size and shape to allow the defoamer to work effectively.

Defoaming challenge

Application points for defoaming can vary in a typical potato processing line but they will be useful from the rock/stone catch to the flume system and steam or abrasive peeling applications through to hydro transport, wash tanks, starch recovery and wastewater treatment.

So defoaming in the potato processing industry is a challenge, says Magazine. There are also regulatory requirements in terms of food safety and ingredients which have to be met and processing aids, like defoamers, need to be considered.
But is it a processing aid or a food additive?

In most cases, it is a processing aid but closer consideration to residual in the final product may need to be defined to determine the possible status as a Food Additive.

This status is also based on intended affect on the antifoam in the final product – if any – as well as residual in the secondary animal and pet food streams from the process.

This topic continues to be a growing discussion point by consumers and government agencies globally, and its use is to control foam formation while conserving and re-using water.

The more water is re-used, it should follow that the more defoaming agents will be needed as impurities concentrate .
But the good news for users of EFC defoamers, concludes Magazine, is that through proper analysis of the application and the proper selection of the antifoam or defoamer, they can reduce water usage while also lowering defoamer costs and usage while giving an improved product quality.

Reduced waste water treatment costs and increased starch available for recovery along with the correct food safety requirements and certification complete the advantages.