Homogenization of milk: Low pressure homogenization (High-speed mixing, ultrasonics, microfluidizers, membrane emulsification)

Homogenizers function as mixers that reduce particle size or force immiscible liquids to mix. Pressure imparted on a product by the homogenizer is largely determined by pump pressure or flow diversion through valves and nozzles. In the case of low-pressure homogenizers, fluid velocity is incremented which reduces overall pressure. In addition to the valve homogenizers commonly used in the dairy industry, a number of emulsifying and homogenizing systems that employ different operating principles are available. High-shear blenders and mixers find wide application in the dairy and related industries for the preparation of coarse pre-emulsions. Colloid mills, which operate on the rotor–stator principle, are used for homogenizing medium- and high-viscosity systems, for instance in the preparation of caseins and caseinates. Ultrasonic waves can be used for either preparing emulsions or reducing the size of existing emulsions. For preparing emulsions with extremely small fat globules and very narrow size distributions, microfluidization can be used, where fluid streams are forced to collide at high pressure. Emulsions with extremely monodisperse size distributions can also be prepared by membrane emulsification. Principles and potential applications of so-called low pressure homogenization technologies are outlined in this article.