We’ve all made the mistake of leaving a container of ice cream on the kitchen counter for a bit too long. Sure, you can refreeze the half-melted treat, but you may find that the texture is far more crunchy than delectably creamy afterward. The culprit is overly large ice crystals. Scientists at the University of Tennessee think they’ve found a plant-based additive to stop the formation of these crystals, and it’s more effective and cheaper than the additives currently used by ice cream manufacturers. The researchers presented their work at this past week’s meeting of the American Chemical Society in San Diego.
“Food science is not cooking,” Tao Wu, a food scientist specializing in carbohydrate chemistry, said during a press conference. “It’s a multi-disciplinary field that uses chemistry, biology, and engineering to solve real-world problems in the production of food. For instance, we must use good chemistry knowledge to produce high-quality ice cream.”
The basic science involved in making ice cream is well known. (Physics students have even been known to use liquid nitrogen to make their own ice cream in the lab.) Just heat milk, cream, and sugar until the sugar dissolves; cool the mixture; and add any flavorings. Then slowly churn that mixture as it freezes. This adds air to the mixture, inflating the volume (overrun). The best ice creams, including gelato, have an overrun of less than 25 percent compared to cheap commercial ice creams, where the overrun can be as high as 100 percent. That higher overrun is why cheap ice creams melt more quickly and don’t store as well. Finally, pack the soft ice cream mixture into containers for the final step in the process (hardening).
All ice cream contains ice crystals, but ideally, you want the smallest crystals possible to ensure a creamy rather than crunchy texture. The rapid chilling and churning process generally results in tiny seed crystals. Problems arise when ice cream melts and then refreezes—a process called recrystallization. If refrozen ice crystals become larger than 50 micrometers, the dessert will take on that undesirable crunchy texture.
To ensure ice cream stays creamy, manufacturers typically add emulsifiers like lecithin and stabilizers like guar gum, locust bean gum, carrageenan, and pectin. These stabilizers help the ice cream retain moisture during storage and slow the growth of ice crystals. However, “These stabilizers are not very effective,” Wu said. “Their performance is influenced by many factors, including storage temperature and time, and the composition and concentration of other ingredients. This means they sometimes work in one product but not in another.”
Further, according to Wu, it isn’t clear exactly how these added ingredients interact and inhibit ice recrystallization. The focus of this latest research is to identify and test better alternatives.