Homogenization (chemistry)

Homogenization or homogenisation is any of several processes used to make a mixture of two mutually non-soluble liquids the same throughout.^[2] This is achieved by turning one of the liquids into a state consisting of extremely small particles distributed uniformly throughout the other liquid. A typical example is the homogenization of milk, wherein the milk fat globules are reduced in size and dispersed^[3] uniformly through the rest of the milk.^[4]

Homogenizing valve, a method to homogenize at high pressure^[1]

Definition

Homogenization (from "homogeneous;" Greek, homogenes: homos, same + genos, kind)^[5] is the process of converting two immiscible liquids (i.e. liquids that are not soluble, in all proportions, one in another) into an emulsion^[6] (Mixture of two or more liquids that are generally immiscible). Sometimes two types of homogenization are distinguished: primary homogenization, when the emulsion is created directly from separate liquids; and secondary homogenization, when the emulsion is created by the reduction in size of droplets in an existing emulsion.^[6] Homogenization is achieved by a mechanical device called a homogenizer.^[6]

Application

One of the oldest applications of homogenization is in milk processing.^[7] It is normally preceded by "standardization" (the mixing of milk from several different herds or dairies to produce a more consistent raw milk prior to processing).^[7] The fat in milk normally separates from the water and collects at the top. Homogenization breaks the fat into smaller sizes so it no longer separates, allowing the sale of non-separating milk at any fat specification.^[3]

Methods

High-pressure homogenization

In high-pressure homogenization, a liquid product is forced through a narrow orifice under pressures typically ranging from 1,500 to 35,000 psi. This process reduces particle and droplet size through a combination of shear, turbulence, and cavitation. It is commonly used in the dairy industry to homogenize milk, producing uniform fat distribution and improving product stability.^[7]

High-pressure homogenization is also applied in other beverage categories, such as soft drinks and vegetable-based drinks, to prevent the separation of components during storage. Ultra-high-pressure homogenization (UHPH) systems have been developed to further enhance microbiological stability and shelf life.^[8][9]

High-shear homogenization

High-shear homogenization uses a rotor/stator mechanism to apply intense mechanical shear to a product, promoting dispersion and droplet size reduction. This method is widely used in industries such as food, pharmaceuticals, and cosmetics. Rotor/stator mixers typically achieve droplet sizes in the range of 2–5 microns, with finer distributions possible depending on formulation and processing conditions.^[10]

A key advantage of high-shear homogenization is that it can improve emulsion uniformity and stability without altering formulation components. This is especially important for commercial products with fixed or regulated ingredient profiles. In a 2016 study, applying high-shear homogenization at 3600 rpm significantly reduced droplet size, improved viscosity, and eliminated phase separation in oil-in-water emulsions, all while maintaining the original formula.^[11]

See also

• Ultrasonic homogenizer
• French pressure cell press
• Homogenizer
• Cell disruption