Mix substances together and homogenize them.
Can be dissolved to form a single uniform phase.
Dispersion is defined as a mixture in which fine particles are scattered in a continuous phase throughout a different substance or state.
There are three types of liquid dispersions: true solution, colloidal dispersion, and suspension.
TRUE SOLUTIONS: (< 1 nm)
True solutions are ions or small molecules (such as monosaccharides and salts) that are less than one nanometer in diameter dispersed in liquid. They are invisible under any microscope and can pass through most membranes. They are very stable, and the solutions are transparent.
COLLOIDAL DISPERSION: (1 nm to 1000 nm)
Colloids are formed when one substance (liquid, solid or gas) is dispersed through another, but does not combine to form a solution.
Emulsions are an example of colloids composed of tiny particles suspended in another immiscible (unmixable) material. Strictly speaking, the term colloidal refers to particles with at least one dimension ranging from 1 nm to 1 µm.
Examples: whipped cream, mayonnaise, milk, butter, gelatin, jelly, muddy water, plaster, colored glass, etc.
SUSPENSIONS: (> 1000 nm)
Simply defined as a heterogeneous mixture of two substances in which one is dispersed into the other, suspensions involve particles larger than those found in solutions, typically over 1,000 nm (1 micron).
Common dispersions widely used in manufacture of food products:
powder dispersion:
Powder dispersion is the mixing process that involves the introduction of dry material into water or other liquids. Can be classified as easy to disperse and difficult to disperse.
Some examples:
Difficult-to-disperse powders:
- Xanthan gum (common in salad dressings and sauces). It helps to prevent oil separation by stabilizing the emulsion, although it is not an emulsifier. Xanthan gum also helps suspend solid particles. Xanthan gum helps create the desired texture in many ice creams.
- Pectin improves the taste and texture of yogurt by serving as a stabilizer and gelling agent and increasing the shelf life of yogurt.
- Carboxymethyl cellulose plays an emulsifying stabilizing role in drinks containing fat and protein.
easy-to-disperse powders:
Generally, do not present lumping problems and require moderate shear.
- Granulated sugar
- Milk powder
Liquid dispersion:
Dispersion of two immiscible liquids is called emulsification (Milk is a commonly cited example of an emulsion)
“The use of the right mixing equipment is key to not only prevent lumping, but also to increase productivity, enhance product quality and reduce energy costs”.
WHAT IS A HIGH SHEAR MIXER?
Rotor/Stator mixers, also called high shear mixers, are comprised of a rotor turning at high speeds within a stationary stator.
The product is suctioned through the inlet and the rotor pushes it to the stator. The mixer creates mechanical and hydraulic shear by continuously drawing product into the rotor and expelling them radially through the openings in the stator.
Why do some powder form lumps when added to water?
One problem arises when dispersing difficult powders. The powders float and begin to hydrate nearly as soon as they are added to water, this can result in the formation of sticky masses “fisheyes” or lumps with a hydrated skin and dry core, where the water couldn't penetrate.
