B

Figure 2. (a) Flow rate of a mayonnaise through a colloid mill increases with in-feed pressure. The gap between the rotor and the stator was 0.010 inches (0.254 mm). Density was 920 g/L. (b) Viscosity is reduced when the in-feed pressure is increased, causing an increase in flow rate and reduction in residence time. Source: From the research laboratory APV Americas-Homogenizers.

Mayonnaise contains 65% or more vegetable oil. The colloid mill produces the best combination of fluid processing conditions to make a good emulsion at this oil level. If this high oil level emulsion is processed on a homogenizer, then the results are poor. The homogenizer makes too small a droplet size, which leads to instability and separation of the emulsion because the natural emulsifier in mayonnaise cannot stabilize the large interfacial area generated. The colloid mill produces a droplet size range that makes a stable, viscous product. On the other hand, a salad dressing at 30% oil can be made on a homogenizer or a colloid mill. Because of the high viscosity usually associated with a salad dressing, a small oil droplet size is not necessary, and the energy level of a colloid mill is adequate to make this type of emulsion.

There are many other products made on the colloid mill. In the cosmetic industry colloid mills are used for making creams and lotions. In the chemical industry they are used for preparing bituminous emulsions, silicone oil emulsions, grease, and pigment dispersions. In many of these applications, the colloid mill works well because of high dispersed phase concentration in the product, high viscosity components, and moderate droplet size requirements.

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