Half of ice cream is air in the form of air cells. About two thirds of it is in the form of ice crystals. So it’s a foam, it’s a dispersion, and it’s an emulsion—about twelve percent of ice cream is in the form of fat that’s spread out in small globules. It’s a very complex multi-phase system.

A multi-phase system that needs to be creamy. “There are a lot of factors that affect creaminess,” Hartel explains. “The fat content is one, the ice crystals is another. If we have very large ice crystals, then it’s a coarse ice cream, not a smooth ice cream, and not a satisfactory eating experience. The smaller the crystals are, for the most part, the creamier the taste, the smoother the taste.”



One enemy of creaminess is heat shock. “When you take ice cream out of the freezer and let it sit for a while, and some of the ice cream melts, and then you put it back in the freezer…we have more ice that’s being formed, but not in the form of new ice crystals. It’s forming around the existing ice crystals, so all the remaining ice crystals get bigger,” Hartel says. “The ultimate outcome is that you feel ice crystals in your mouth when you eat the ice cream, and that’s not a good eating experience.”



Now, a new technique from Switzerland for battling heat shock is making ice cream that can stay creamy longer. Described in Discover Magazine, the patented process pioneered by Erich Windhab, a food engineering professor at the Federal Institute of Technology in Zurich, churns and pumps the ice cream out of an extruder at lower temperatures and with smaller ice crystals than the traditional process allows.



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