Ice cream is a complex, three-phase food system in which ice (solid), air (gas) and unfrozen water (liquid) coexist. Much that makes ice cream an indulgence derives from its relatively high fat content, which can range from 10 to 18 percent in premium varieties. In addition to its role in taste and flavor development, fat is crucial to ice cream's texture. No wonder, then, that most low-fat varieties fail to offer the same taste sensation.
Lately food scientists have found clever ways to experiment with unsaturated fats aiming to bring consumers the full satisfaction of ice cream with fewer of the health consequences associated with saturated fats. Solid fat builds structure in ice cream via partial coalescence, which occurs when two fat droplets collide and fuse only “at their hip,” remaining distinguishable from each other. The fusion is mediated by crystals that protrude from the surface of the spherical droplets—imagine the thorns of a prickly pear—that pierce neighboring droplets as they collide. These droplets then aggregate and deposit onto the surface of air bubbles and stabilize the frozen foam. In this way, partial coalescence enables ice cream to taste creamier, hold its shape and melt more slowly.
Given that unsaturated fats are liquid, the original thought was that they would not be good candidates to make ice cream less of a sin. Recent research, however, has the skeptics thinking twice. New studies led by Douglas Goff of the University of Guelph in Ontario suggest that plateletlike or needlelike droplets (as opposed to spheres) that contain 40 to 60 percent unsaturated fats are very effective at building structure in ice cream. Such fats can be blends of any highly unsaturated oil (such as high-oleic sunflower or canola oil) and saturated fats such as coconut oil or cocoa butter. Platelets formed only when Goff's team added commonly used unsaturated emulsifiers, such as glycerol monooleate, which are thought to force the fat crystals to grow preferentially in one dimension, hence generating the needlelike profile. Because of their shape, the amount of fat needed to create a stable frozen foam (via partial coalescence) decreases. This opens up the possibility for low(er) fat, creamy, slow-melting ice cream.