TABLE OF CONTENTS A typical ice cream consists of about 30% ice, 50% air, 5% fat and 15% matrix (sugar solution) by volume. It therefore contains all three states of matter: solid ice and fat, liquid sugar solution and gas. The solid and gas are small particles - ice crystals, fat droplets and air bubbles - in a continuous phase, the matrix. To understand the creation of the microstructure during the manufacturing process we must first introduce some concepts from the physical chemistry of colloids, freezing and rheology (the study of the deformation and flow of materials).
Colloidal dispersions consist of small particles of one phase (solid, liquid or gas) in another continuous phase. The particle size may range from nanometres to tens of microns. There are eight different types of colloidal dispersion, summarized in Table 2.1.
| Continuous phase | Dispersed phase | Name | Examples |
|---|---|---|---|
| Solid | Solid | Solid sol | Ruby, glass, composites, ceramics, bone |
| Solid | Liquid | Solid emulsion | Bitumen, asphalt, opal, pearl, jelly |
| Solid | Gas | Solid foam | Expanded polystyrene, pumice |
| Liquid | Solid | Sol | Ink, paint, blood, toothpaste, mud |
| Liquid | Liquid | Emulsion | Milk, mayonnaise, cream |
| Liquid | Gas | Foam | Head on beer, bubble bath |
| Gas | Solid | Aerosol | Smoke, dust |
| Gas | Liquid | Aerosol | Mist, fog, clouds, deodorant |
Colloidal dispersions have a very large surface area for their volume. Therefore the surface properties of the phases have a large influence on the properties as a whole. Ice cream is simultaneously an emulsion (fat droplets), a sol (ice crystals) and a foam...
