This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Aging. Sherwood and Smallfield have reported that in some cases aging shows an increase in viscosity of the cream whereas in others it does not. When the viscosity is increased the fat globules are larger and clump. They have found that agitation of the cream reduces the size of the fat globules and the viscosity of the cream. Mortensen states that cream just separated from fresh milk should be aged 24 hours before it is used in ice cream, even if it is not pasteurized. Aging also gives a cream that whips better. The viscosity of a cream increases noticeably for about 6 hours after it is separated and then increases at a slower rate.
Homogenization. Williams lists the benefits of homogenization, as applied to ice cream, under 6 heads as follows:
1. Increased viscosity.
2. Reduction in time required for aging.
3. Less physical and mechanical loss of fat.
4. Better whipping qualities.
5. Better freezing qualities.
6. Greater uniformity and palatability.
Ice cream made from homogenized cream is smoother and has smaller crystals. In homogenization of the cream the fat globules are broken up. As the size of the globules is decreased the surface area increases. The fat globules are surrounded by a film of protein. After homogenization, owing to the increased surface, a larger amount of protein is held in the film around the fat particles. The increase in the number of the fat globules and the protein held in the film increases the viscosity of the cream. After homogenization the cream should not be agitated. The higher the pressure used during homogenization, the greater the viscosity obtained in the cream.
With homogenized cream, less fat and less milk solids not fat can be used and a texture obtained that is as good as that from an unhomogenized cream with higher fat content and with higher milk solids.
Pasteurization. Pasteurization decreases the viscosity of the cream. Cream needs to be aged after pasteurization before it is used in ice cream.